Farnell dtv 20 manual

Kit includes all components and 48 step motor. Chip is pre-programmed with demo software, then write your own, and re-program the same chip! Circuit accepts inputs from switches etc and drives motor in response. Also runs standard demo sequence from memory. Use as Data! Logger or as a test bed for many other 16F projects.

Fax: It hardly seems any time at all since we were all worrying about how to celebrate the new millennium and now the numbers have moved on by two. Of course, regular readers will know that every other year we publish a Teach-In series with the intention of providing a wide range of educational material on electronics.

TI will be all about interfacing to the outside world and will look in some depth at sensors, how they work, how to use them and the data they can supply. This new series is being produced by a team of writers co-ordinated by Alan Winstanley and drawing from the vast range of knowledge of the electronics department at Hull University.

Some months have been spent planning the content and working on demonstration projects for readers to build and test. The course will employ a Pico Technology PCbased oscilloscope to provide PC displays of the various parameters to be measured.

The scope will be available to readers at a Special Offer price. It will look at a range of circuit topics from Basic Principles through Op. Each part will have associated labs and projects. The new series will assume some basic knowledge of electronics, so if you want to start right at the very beginning with a series that requires no previous knowledge, you will need to look at the previous Teach-In, which is available on CD-ROM Teach-In — see page for details. EPE can also be purchased from retail magazine outlets around the world.

Tel: Subscriptions start with the next available issue. For past issues see the Back Issues page. These are finished in blue p. Normally sent within seven days but please allow 28 days for delivery — more for overseas. Send, fax or phone your card number and card expiry date with your name, address etc. Or order on our secure server via our UK web site. Overseas customers — your credit card will be charged by the card provider in your local currency at the existing exchange rate.

We regret that we cannot provide data or answer queries on articles or projects that are more than five years old. Letters requiring a personal reply must be accompanied by a stamped self-addressed envelope or a selfaddressed envelope and international reply coupons. All reasonable precautions are taken to ensure that the advice and data given to readers is reliable.

We cannot, however, guarantee it and we cannot accept legal responsibility for it. We advise readers to check that all parts are still available before commencing any project in a back-dated issue. The Publishers regret that under no circumstances will the magazine accept liability for non-receipt of goods ordered, or for late delivery, or for faults in manufacture. The laws vary from country to country; readers should check local laws. If they need to extend the operating time, they simply buy another battery and carry them both around.

A typical camcorder battery provides an operating time of 45 minutes, including using the zoom lens and rewinding the tape every so often to review the results. Two batteries would still only give 90 minutes of operation. Although highcapacity batteries are available, they are an expensive option. Charging may be effected either from the mains or a 12V d. On the front panel there are mains and 12V d. In camera mode, a further l. If you measure it, the voltage will be somewhat higher than the stated nominal value when the battery is fully charged.

However, for the sake of battery life, this should be regarded as a peak figure. It is not advisable to measure the current directly unless you are certain of being able to maintain the correct polarity and avoid short-circuiting the battery.

Two 6V batteries are used rather than a single 12V one because these may be charged simultaneously from a 12V car supply. A single 12V battery would not be satisfactory because, when the battery was wellcharged, there would be no voltage difference to drive the current through.

The specified batteries have a capacity of 7Ah but others could be used with a proportional change in operating and charging time. However, do not use a capacity less than 4Ah.

Note that a pair of 7Ah units provides the equivalent of about 10Ah for a 6V camcorder because the circuit delivers around 80 per cent of the total energy to the load. In fact, doing this extends their service life. Leadacid batteries also hold their charge much better than the nickel-cadmium type. If Everyday Practical Electronics, October lead-acid batteries are left charged, they will not self-discharge significantly over a period of several months.

The mains supply is connected via transformer T1. The 12V a. With the specified transformer this gives about 15V d. When a 12V d. Diodes D3 and D4 also provide isolation between the two input sources so that current from one cannot possibly drain into the other.

Light-emitting diodes D1 Mains and D2 12V draw current direct from their respective supply, with current-limiting effected by resistors R1 and R2. With the values specified, the theoretical limit is approximately 1A. These route current to the individual 6V batteries, B1 and B2, at a maximum of about mA each. This is configured to provide the correct output voltage to charge the battery pack.

A voltage higher than that required appears at the output, pin 5. Current then flows through three resistors all labelled R3 connected in parallel and the excess voltage is developed across them. This forms the current-limiting aspect of the regulator. If the current tends to rise, the voltage across resistors R3 will increase. With a battery in a poor state of charge, the difference between its own voltage and that of the charger output is significant and this drives current through the battery.

Without current-limiting, the current would be quite high due to the very small resistances involved, and could be destructive to circuit components or to the batteries themselves. Everyday Practical Electronics, October from discharging back into IC1 when the supply is switched off. As charging progresses, the current flowing into the batteries reduces, to about 50mA when the charging is nearly complete. Some 90 per cent of the required charge is delivered before the current reduces significantly.

With the specified batteries, this takes 15 to 20 hours approximately and in most cases the batteries will then be regarded as fully charged. While charging, switch S1c disconnects the subsequent circuit so current does not drain into this unnecessarily. Switch S1a now disconnects the charging supply if it has been left switched on. Switch S1b connects the two 6V batteries in series so that nominally 12V appears across them, which S1c then connects to the following part of the circuit.

As the batteries discharge, their combined terminal voltage falls slightly. The voltage and hence charge is monitored by three sections of quad op. All three inverting inputs pins 2, 6 and 9 are connected together and are set at 5V by voltage reference IC2. Resistor R10 limits the current flow though IC2 to ensure its correct operation. The non-inverting inputs pins 3, 5 and 10 are connected to points along the potential divider chain which comprises resistors R6 to R9 joined in series across the supply.

D7 to D9 turned on. The l. When the voltage falls below each threshold the relevant output goes low and its associated l. If all three l. In use, it will be found that high and medium charge are shown for a relatively long time but low charge is shown for only a short period. Compared with the linear regulator used for charging the batteries, the switching type is much more efficient, by around 80 per cent or more. At the same time, less waste heat is produced.

The regulator contains an on-chip oscillator which produces a stream of pulses. Their frequency is determined by the value of resistor R15 and capacitor C7 connected in parallel to pin 5 oscillator. With the values specified it is about kHz. Cost Guidance Only excluding batts. BYW80 fast recovery diode see text 5W Zener diode see text LCV voltage and current regulator The output appears at pin 7 and is smoothed by inductor L1 in conjunction with twin capacitors both labelled C8 connected in parallel.

During this time, diode D10 is reversebiased and has no effect. When the output pulse falls, the resulting negative-going current is conducted through diode D10 rather than from the inductor and the load current is maintained from the stored energy. The process then repeats. The specification of D10 and capacitor s C8 is especially important. Due to the rapid switching involved, the diode must be capable of switching on and off at high speed. It must therefore be of the fast recovery type and have a generous current rating 8A minimum.

Capacitor s C8 must have a low impedance at kHz and a working voltage of 50V d. These facts must be remembered if different components to those specified are used. This is one input of an on-chip comparator the error amplifier. Preset VR2 is adjusted so that the output voltage is at the required value.

Resistor R14 and capacitor C5 connected in series to pin 3 frequency compensation determine the regulation loop gain characteristics. The values specified are those recommended by the manufacturer. Capacitor C6 connected to pin 6 soft start prevents a current surge when the regulator is switched on. This provides protection in the event of some catastrophic circuit failure resulting in a sudden rise in output voltage.

The Zener breakdown voltage is selected to be about 25 per cent higher than the output voltage so that it does not normally conduct. If the voltage tries to rise for some reason, the Zener diode clamps this at its breakdown voltage and a large current can flow through it. The current would be much greater than could be handled continuously but the fuse should blow quickly enough to prevent destruction of the Zener.

This is not guaranteed to be effective but to provide the best chance of success, a fast-blow fuse should be used for FS3. Also, the value of the fuse should be only a little greater than the maximum load on the output. Great care should be taken over all aspects of construction to prevent faults occurring in the first place. Because of their rapid on-off action, switching regulators tend to generate radio-frequency interference r.

This can cause noises from the loudspeakers of radio equipment connected to the same supply or in the vicinity of the circuit. This is not a problem here because the mains supply is disconnected when the regulator is operating. Also, interference cannot be radiated because the circuit is enclosed in an earthed metal box. The topside component layout and full size underside copper foil track master are shown in Fig. Printed circuit board component layout and full-size copper foil master track pattern for the Camcorder Power Supply.

Assemble the board in order of component size, observing the correct orientation of polarity-conscious components. It would then be a simple matter of de-soldering it and replacing it with one of a different value. The value of capacitor C5 33n may not be readily available. Provision has therefore been made to solder two capacitors in parallel, 10n and 22n, to give nearly the same value. There are different manufactured styles for voltage reference device IC2.

Some have three leads instead of two, in which case refer to the pin-out of the particular device which your component supplier should have available and cut off the unwanted lead. Note that IC1, IC2 and IC3 are staticsensitive, so touch something which is earthed such as a metal water tap before handling their pins.

If the leads are too short, extension leads can be added, as was the case with the prototype. A heatsink is needed for diode D10 but not shown in the photograph and this may be a piece of sheet aluminium having minimum dimensions of 15mm by 40mm bent through right angles and attached so as to maintain a clear gap with all internal parts.

Solder 15cm pieces of stranded connecting wire of 3A rating minimum to switch S1 pads. Use different colours to avoid errors later. Note that the metalwork is used as a heatsink for the regulators so these must be placed flat against the box.

It is very important that no part of the circuit makes contact with the case. The 12V input and output connectors may be of any polarised type but must be sufficiently rated for the expected load. The 12V and camcorder connectors must be of a different pattern so that the cables cannot be interchanged. Mount the p.

Using a suitable mounting bracket, attach the batteries securely in position. Make sure there is a clear space between the terminals and everything else. Partially discharged batteries should be used initially to allow correct testing of the charging circuit. Refer to Fig. Insulate all mains connections so that they cannot be touched. Make up a lead or use a ready-made one to connect the car cigar lighter socket to the 12V input observing the correct polarity. It is essential for an in-line fuseholder and 3A fuse to be included in this lead.

Interwiring between circuit board and off-board components. Use stranded mains-type wire of 3A rating minimum. Whenever a mains supply is plugged in, the case must be fully enclosed so that there is no access to internal parts. If the ammeter reads less than mA, no action is needed.

If it is too high, experiment by increasing the value of the resistor in the R3 group until a satisfactory reading is achieved. With the current limit set, permanently link TP1 to TP2. Adjust preset VR2 until the correct voltage is obtained across the output terminals SK2.

If fuse FS3 blows, or regulator IC4 becomes hot, switch off immediately. Investigate and correct the fault before proceeding. Note that the presence of Zener diode D11 will limit the maximum output voltage. It will also increase the current flow if IC4 tries to raise the voltage above the Zener threshold. Check all aspects of operation and make certain the unit and camcorder operate correctly. Disconnect the 12V test supply and plug Internal view showing the p.

Check that the output voltage at SK2 is still the same. Now fully charge the batteries using the mains supply. After 30 minutes, then at hourly intervals, unplug the supply, remove the lid and check that nothing is excessively hot. If necessary, drill ventilation holes in the case but make sure they are small enough so that nothing conductive could be pushed through and touch a mains connection. Completed circuit board. Note the l. When in use, the batteries need recharging when only the red l.

The unit should be removed from the camera bag while charging. This is because the bag would insulate the case and could cause the unit to overheat. This ring binder uses a special system to allow the issues to be easily removed and re-inserted without any damage.

A nylon strip slips over each issue and this passes over the four rings in the binder, thus holding the magazine in place. The binders are finished in hard-wearing royal blue p. They will keep your issues neat and tidy but allow you to remove them for use easily. Send your card number and card expiry date plus Switch Issue No. Order Ref: Pack of 3. Order Ref: 8. Pack of Single pole changeover. Approximately 12in. Suitable for up to 6 hours.

LT44, impedance ratio 20k ohm to 1k ohm; centre tapped, 50p. Pack of 2. Order Ref: 11R Order Ref: GR Order Ref: 7RC Order Ref: 7FC Good length flexible lead. Order Ref: D This tester measures d. Also tests transistors and diodes and has an internal buzzer for continuity tests. Comes complete with test prods, battery and instructions.

Order Ref: 7P Order Ref Enables you to plug 2 telephones into the one socket for all normal BT plugs. Order Ref: 1. Size 60mm long, 30mm diameter. Very powerful, operates off any voltage between 6V and 24V D. Speed at 6V is rpm, speed controller available. Order Ref: 3P Ideal for putting on a van, a tractor or any vehicle that should always be seen. Uses a Xenon tube and has an amber coloured dome. Separate fixing base is included so unit can be put away if desirable.

Order Ref: 5P Rated at 9V 1A, this plugs into a 13A socket, is really nicely boxed. Order Ref: 2P These are suitable for D. They reduce the speed by intermittent full voltage pulses so there should be no loss of power. Order Ref: 12P Order Ref: 20P This is proper heavy duty cable for running around the skirting board when you want to make a permanent extension. This has AC voltage output so is ideal for operating most doorbells. The unit is totally enclosed so perfectly safe and it plugs into a 13A socket.

Internally generates voltages which enable you to read insulation directly in megohms. Order Ref: 7. The first is Oscillator 87F. This has an output, continuous or interrupted, of 1kHz. It is in a plastic box size mm wide, mm high and 50mm deep. Order Ref: 7R1. The other is Amplifier Ref. This is in a case size 80mm wide, mm high and 35mm deep.

Order Ref: 7R2. We have thousands of relays of various sorts in stock, so if you need anything special give us a ring. A few new ones that have just arrived are special in that they are plugin and come complete with a special base which enables you to check voltages of connections of it without having to go underneath. We have 6 different types with varying coil voltages and contact arrangements. All contacts are rated at 10A V AC. Another relay just arrived is extra small with a 12V coil and 6A changeover contacts.

It is sealed so it can be mounted in any position or on a p. Order Ref: FR Order Ref: 2. You can have a set of 10 leads, 2 each of 5 assorted colours with insulated crocodile clips on each end. It is 55VA so that is over 4A which is normal working, intermittently it would be a much higher amperage. Order Ref: 3. Nicely cased, free standing, has internal alarm which can be silenced.

Also has connections for external speaker or light. Order Ref: 10P Order Ref: 9. Motor is mounted on the gearbox which has interchangeable gears giving a range of speeds and motor torques. Commsim is a powerful and easy to use Windows-based simulation environment for modelling analogue, digital or DEPT mixed-signal networks.

Commsim offers hundreds of communication and maths blocks for powerful yet intuitive design, so modelling and simulation can be performed, say Adept, without having to write a single line of code.

The product reflects the new system level approach currently being taught in colleges and universities throughout the world to introduce electronics and its real world applications to engineering students. Consistent with the approach taken by other renowned Electronics Workbench products, Commsim offers both hierarchical modelling and embedded compound blocks, facilitating rapid prototyping.

Once designed the system can be simulated to determine its performance under a variety of operating conditions.

For more information contact Anna Moorhouse, Dept. E-mail [email protected] Web: www. E-mail: [email protected] Web: www.

Please mention EPE when contacting. For more information, browse w w w. Everyday Practical Electronics, October the chance to access the Internet more quickly, and do so with a single conventional phone line without blocking speech calls. A V92 modem with Quick Connect can halve tiresome logon times. Modem on Hold pauses the PC while it is Internet surfing, to let the user take an incoming speech call on the same phone line. When the talking stops, the PC clicks back to the Internet without the need to redial.

The International Telecommunications Union sets the V standards which ensure that modems round the world talk to each other. V90, as now widely used, pushes the data capacity of phone lines to their practical limit, by receiving at up to 56Kbps and sending at up to If the phone line has a callwaiting service, which sends bleep tones down the line to warn that someone is trying to make a voice call while the line is engaged, existing modems often mistake call-waiting for a disconnect tone and hang up on the Internet, without giving the surfer any choices.

A V92 modem solves both these problems with non-volatile memory which builds a library of previous settings. When the modem dials an Internet service with matching software they quickly recognise a known situation and skip the rest of the handshake.

The V92 modem also recognises a callwaiting tone for what it is, puts the Internet connection on hold and then uses the stored settings to reconnect quickly when the speech caller hangs up. Connexant, the spin-off from modem chip maker Rockwell which has driven V92, expects ISPs to offer the services by the end of this year.

Some modems already promise V92 in the small print. Clearer publicity might spoil V90 sales. A series of small metal ridges is built into the road, like miniature sleeping policeman speed humps. The ridges are around 15mm apart and in a pattern that matches the peaks of a musical waveform. So the car vibrates to play a tune. If slightly different sets of ridges are formed, to the left and right of the road, the car vibrates in stereo sympathy. The ridges can be temporary, on a mat laid on the road alongside an advertising sign, to play a matching jingle.

It provides a timely, digestible review of the current state of knowledge about possible health effects of mobile phone handsets and the associated mobile transmission masts. There are documentary style interviews with leading scientists in the field, and members of the Independent Expert Group on Mobile Phones whose report was published last year.

The video has been produced professionally and contains graphics and other material to illustrate points made. For example, there are useful graphic sequences showing how mobile phones work, what the possible heating effects could be in the head and how people are exposed to transmissions from masts.

NRPB felt there was a need for a video giving straightforward, factual information about mobile phones and health issues. The expanded TechnoLook range includes higher magnification and semi-digital models, taking the first step towards a fully digital microscope. Our aim was to create an easy to use product that could be connected to a PC, eliminate eyestrain and reduce neck and back problems.

TETRA is the new digital radio system for use by commercial organisations and the emergency services. Its operation results in pulse modulation of the r. It has noted that the signals from base stations are not pulsed whereas those from hand portables and from terminals built into vehicles are. Web: www. AST Without doubt some parts e. Hopefully, adequate ventilation will be available to help with the throughflow of air. Obviously, bolting such parts to a steel or aluminium chassis will help dissipate heat.

Although a wide variety of parts e. A TO-3 can style regulator sawn off to reveal the i. The idea is to carry heat away from the part that matters most — the semiconductor junction or i. A typical heatsink system contains the elements described in the photo.

This could represent any power transistor containing a junction, or say a voltage regulator chip such as a the TO-3 type opened up for the photograph.

The junction is at the heart of the package, but unfortunately for us, various elements of the system hinder the passage of heat and have to be accounted for. A typical assembly showing how the thermal resistance is divided between the device and heatsink. The junction of a TO-3 device will be fixed to a steel base, but the case might also be packed with thermal conductive grease to help improve reduce the thermal resistance; it is usually just full of fresh air though.

A junction mounted in a TO or TO device will be embedded in a plastic resin, not known for its heat conducting properties but the metal tab is there to help with heatsinking. The differences in thermal efficiencies are obvious. This means an insulating washer as shown in the photo, perhaps with a smear of thermal conductive grease. In some catalogues, it is shown as Rth.

Some typical heatsinks are shown in the photo, including types intended for integrated circuits. This directly affects our calculation and it depends on ventilation and the proximity of any other hot devices. Suddenly, those heatsink ratings need scrutinising carefully!

If this should be borne in mind by the budding value is exceeded then heat may not be disdesigner. Computer the heatsink specification. This factor enthusiasts will be well aware of the need relates to ventilation and cabinet or circuit to fan-cool processor and video chips and board layout. What effect Circuit Surgery is your column. If you would using the smaller TO package have any queries or comments, please have instead?

The higher thermal resiswrite to: Alan Winstanley, Circuit Surgery, tance means that a better heatsink would be Wimborne Publishing Ltd. E-mail no attachments [email protected] Please somewhere along the line. Larger heatsinks indicate if your query is not for publicaare costlier and take up more space, implytion. A personal reply cannot ing a larger and more expensive cabinet.

Name and Address Post Code Everyday Practical Electronics is published on the second Thursday of each month and distributed S. The board has been introduced following readership suggestions about how the original Mk2 board could be beneficially extended to allow its greater use as a PIC design development facility.

The Mk2 board was principally designed as a platform on which various PIC types could be programmed via the accompanying software. Whilst it provided limited access to the pins of an on-board PIC16x84 microcontroller, allowing it to be used in situ as the rudimentary heart of a developing hardware circuit, it did not offer direct access to all pins of the larger PIC16F87x family that could be programmed on it.

This new board design is intended to rectify this situation, allowing the four PIC sizes that it can accept to be hard-wired not only to additional on-board hardware, but also external components in conjunction T HIS with an optional plug-in breadboard.

Direct connection of the programming lines can be made to external PIC-controlled circuits under development or final completion such as published EPE PICbased designs. The notable difference between the PIC Tutorial board and that of Toolkit Mk3 is that the latter, like its Mk2 predecessor, is under complete programming control by the connected PC-compatible computer. The Tutorial board, you may recall, had to be manually switched at different stages of the programming procedure.

Electronically, the circuit is essentially the same as that for the Mk2 board. Connections between the PC-compatible computer and the board are made via the parallel printer port and a standard Typical main screen display of the controlling software described in the page Free supplement to be published next month.

The connections are buffered by IC2a to IC2e, ensuring that the input and output signals are maintained at optimum logic levels. The input signals also have ballast and pull-down resistors, R1 to R8. The ballast resistors protect the connected computer output lines when the board is unpowered. The pull-down resistors provide a 0V bias to the buffer inputs when the computer is unpowered, or the port connector is unplugged.

Data and clock signals are brought in via printer port lines DA0 and DA1. A fifth port line connection, ACK, sends signals back to the computer during PIC data reading, such as is required in code verification and disassembly modes.

This allows the software to check that the printer port cable is connected and the p. The logic is illustrated in the block diagram in Fig. At other times they are disconnected from the port and routed as PIC data lines to any development circuit connected to them. This prevents the two PIC lines, and the computer, from being adversely affected by external circuit loads during programming.

Visual advice that the PIC is in programming mode is provided by l. D8, being turned on during programming and data read back. Block diagram illustrating the signal connection logic.

The bus lines are terminated at pin header strips or terminal pins to which external circuit components can be connected. The 8-pin socket has been included at reader suggestion. There are several small PICs that are likely to be suitable for programming via this socket, although none have been tested. Consult data sheets for PIC types not specifically mentioned here by name. It is recommended that ZIF sockets are installed in any PIC position which is likely to be regularly used but they are not made in 8-pin size so far as is known.

Pin-out identities for the PIC sockets on the p. The PIC may also be reset manually by pushbutton switch S1. This facility is useful during code development, allowing the PIC to be repeatedly reset in order that some programmed actions can be observed from the beginning.

See 1k 6 off k 4 off n ceramic disc 2 off 4m7 radial elect. S1, S3 to S6 S2 L. Also connected to this pin header are VR2, the l. It is the same l. If ordering this l. Crystal X1 is used in conjunction with capacitors C8 and C9. It is recommended that a crystal socket is used on the p.

It is also recommended that a p. Switch S2 allows crystal or RC oscillation mode to be selected. It should be noted that the PIC requires its Configuration bits set to different logic values in relation to the oscillator type used.

The components are shown in Fig. Their emitters are grounded and you may connect their opencollectors to other circuits that require currents greater than the PIC can provide about mA maximum per transistor, compared to about 25mA per PIC pin — see PIC data sheets for more information on the currents permitted.

The bases can be connected to any PIC pin as required, via the ballast resistors provided. Eight uncommitted l. They all have ballast resistors module RM1 in series, providing enough current for adequate brilliance without overloading the PIC. Referring to Fig. They are normally-open pushbuttons, with 10k9 resistors R17 to R20 in series.

Printed circuit board component layout and full size master track pattern for PIC Toolkit Mk3, showing positioning of optional breadboard. Lastly Fig. This allows additional components to be breadboarded alongside the Toolkit Mk3 board for extended circuit development use.

Also note that regulator IC4 may require a heatsink at higher input voltages and output currents. Thoroughly check the board for assembly errors before inserting the d. Next check the powered board with only regulator IC4 in circuit, then check the power line voltages with voltage converter IC1 inserted as well. From then, fully populate with the other i. Only one PIC should be inserted at any one time.

May your programming dreams be fulfilled! IC4 in Fig. A 1A device IC4 is recommended to provide enough current to power the board and other development circuits connected to it. These inverters generate a modified sine wave, which are considerably superior to the square waves which are produced by most other inverters.

Low Battery Alarm The inverters give an audible warning signal when the battery voltage is lower than The inverter automatically shuts off when the battery voltage drops below 10V 20V for the 24V version. Fuse protected input circuitry. These devices have a number of disadvantages including the difficulty of manufacturing them and using integrated circuit technology. Although in recent years new micro-machining techniques have been introduced that allow for accelerometers to be manufactured as integrated items.

However, these processes involve many masks and etching steps in the manufacturing process. Not only is this complicated but it is also very expensive. New Development In a new development organised by the American National Institute of Standards and Technology in Gaithersburg in Maryland, USA, researchers have overcome the problems of incorporating an accelerometer into an integrated circuit.

The idea is based around a concept that has recently been proposed using the effect of acceleration on natural heat convection. The device uses heat generated from conductors that is transferred into the gas surrounding the device.

It is hermetically sealed to ensure that it is not influenced by external pressure or airflow. The new implementation of this idea uses standard CMOS circuitry and micromachined thermopile or thermistor sensors for temperature sensing. In view of this it is possible to have a completely integrated sensor on a single chip including all the sensing and drive circuitry. This can give significant cost advantages over existing sensors.

Not only this but the sensors show significant performance advantages over other types. These manifest themselves in terms of much lower power consumption and a higher frequency response, extending up to figures of a few hundreds of Hertz rather than a few tens of Hertz when compared to other convective sensors.

Construction The basic device consists of a suspended polysilicon micro-heater, see Fig. When a current is passed through this heated element the thermal difference between the element and the surrounding gas generates a convective flow of gas. When the device experiences some acceleration the change in the convection flow of the gas causes a temperature difference between the sides of the heated element. Temperature sensors placed on either side of the heater element then detect a temperature difference.

The acceleration is proportional to that applied to the device. The temperature sensors can be either thermocouples or thermistors. Both types are equally compatible with CMOS fabrication technology and the interfacing requirements for both types can be accommodated equally as well. However, there are a few differences in the actual construction of the devices.

Thermocouple-based accelerometer. In the device using thermocouples a polysilicon heater encapsulated in a glass passivation is suspended in air. The thermocouple junctions are then located either side and close to the heater. Whilst it would be possible to use a single pair of junctions either side of the heater, greater sensitivity can be achieved by using several thermouples in series.

In the development examples twelve thermocouples were used in series on either side of the heater, giving far greater level of output and hence sensitivity. A different configuration was used for the thermistor-based devices, see Fig. Here two parallel polysilicon resistors were suspended but with an air gap between them.

Two heaters then heated the suspended resistors. These heaters were micromachined to give exactly the required conditions. Concept of thermistor-based accelerometer. Test Conditions The accelerometers were tested under a variety of conditions. One crucial test was that of investigating how the devices operated when they were inclined to the horizontal.

Their operation was tested between plus and minus 90 degrees and for accelerations between zero and 7g. They were also tested over a range of vibration frequencies from 30Hz to 3kHz. Results The accelerometers showed very good levels of linearity. The sensitivity was also good and was found to be almost a linear function of the heater power.

Using a heater running at mW, sensitivity levels of just over mV per g were achieved for the thermocouple devices. Values of 25mV per g were obtained for thermistor devices. Sensitivity is of considerable importance. If values fall too low then the output voltage can become lost in the noise. It was also found that the thermistor device had a higher frequency response than the thermocouple. This is thought to result from the significantly smaller spacing between the sensing devices.

Summary In manufacture these devices only use one additional mask post-processing step. This makes them ideal for easy introduction into production. This will also result in their cost not being significantly above many other specialist devices, and considerably cheaper than other accelerometers.

A further advantage is their robustness as they have no mechanically moving parts. Further development work is still required. The devices can be further optimised and their performance needs to be characterised using different gases, pressures and temperatures.

Other geometries internal to the device also need to be investigated. This new technology shows a significant amount of promise and should enable accelerometers to become cheaper, smaller and more flexible in their use.

An EPE index for the last five years is also available — see order form. Alternatively, indexes are published in the December issue for that year. Where we are unable to provide a back issue a photostat of any one article or one part of a series can be purchased for the same price. Issues from Jan. Flasher — Double Door-Buzzer. Scope D. We can also supply issues from earlier years: except Jan. Where we do not have an issue a photostat of any one article or one part of a series can be provided at the same price.

Switch Issue No. Card No. Card Expiry Date. E-mail: [email protected] On-line Shop: www. Normally supplied within seven days of receipt of order. Everyday Practical Electronics, October Send a copy of this form, or order by letter if you do not wish to cut your issue.

Note: No advertisements or Free Gifts are included. Note: No Free Gifts are included. Order on-line from www. Ds, By Julyan Ilett — An utterly practical guide to interfacing and programming intelligent liquid crystal display modules. Post Code. A bonus article on his life and work written by his eldest son, including many previously unpublished photographs. It requires Adobe Acrobat Reader available free from the Internet — www.

Expiry Date. Send a copy of this form, or order by letter if you do not wish to cut your issue. This article describes how electronics and computers are used to make their work possible. A single road junction might have the layout shown in Fig. Vehicles approaching the junction are detected by inductive loops. The loop is Anyone standing on the pavement outconnected into an a.

Traffic Control Centre in Norwich would This changes when a massive ferromagnetprobably not notice the inconspicuous ic object such as a vehicle is situated above semi-basement entrance.

Yet behind this the loop. Information from This computer keeps the traffic flowing the inductive loops can tell the computer or at least minimises the delays not only the length of the traffic queue at the lights for Norwich city but also for the whole of and also the speed and approximate size of the county of Norfolk. It keeps the pedesvehicles approaching the lights. The comtrians flowing too for, out of the sigputer is programmed to read this data and nals linked to the system, about 50 per cent to use it to decide which lights are to be are pedestrian crossings.

Each junction has its own indecan call on an engineer to handle emergenpendent set of inductive loops, traffic lights cies out of hours. Fortunately for the engiand computer. They are linked by a data cable and they both run according to clocks driven by the mains frequency.

Thus their action is synchronised and takes into account the time delay of traffic leaving one junction and proceeding along the link road to the other junction. Although their local computers independently control these single and double junctions, their action is monitored remotely Fig. At an independently controlled road junction, each by dedicated BT telephone line to the approach lane has three inductive loops.

Here the operator can call up the data for any particular junction. The monitor screen displays a plan of the junction or junctions and pedestrian crossing too. Sitting in the UTCC in Norwich, an operator can check that all of the signals systems in Norfolk are operating correctly. SCOOT In a larger town, where there are more than two junctions close together, the junction computers are connected to and controlled by the central computer at the UTCC.

The kerbside computer controls the lights at the junction but is under the supervision of the control computer in the UTCC. SCOOT also depends on sensing traffic by means of inductive loops.

These are additional loops on the exits from junctions, where traffic leaves the junction to pass along a stretch of roadway to the next junction. In some places there may be two loops close together to allow the speed of the vehicles to be measured. Other kinds of sensor are used where appropriate. On the faster roads there may be Doppler-effect microwave sensors to detect the presence and speed of vehicles. These register vehicles at a distance of about 50 metres.

Doppler-effect sensors are also used on pedestrian crossings to detect the presence of people waiting to cross or actually crossing. Active infrared detectors are also used on pedestrian crossings, as well as sensor mats on the waiting area on the pavement.

The traffic log records all events on the system immediately they occur. This information is also presented for all the junctions in an area in tabular form. The computer also displays a running log of events on the system. A few minutes after the last entry in the figure, the log reported the failure of a Wait lamp at the junction of High Street and Baker Street in Gorleston. The maintenance contractor was automatically alerted to the failure.

The log went on to show that the lamp was replaced nine minutes and 33 seconds later. The data is used only for monitoring and is not stored. In addition to monitoring the system, the controller can call up visuals from a number of remotely controlled video cameras mounted at strategic points in the Norfolk road system.

These cameras have full aiming and zooming features. This allows the operator to sort out any serious problems such as might arise from a traffic accident or football crowd. For an overall view of the situation, the controller watches the map that covers one entire wall of the control room Fig. Lamps on this map indicate the status of the lights at each junction. Because that sequencing is done by software, rather than by mechanical means or logic circuits, it opens up all kinds of possibilities.

SCOOT allows for a large number of different plans to be available for each junction and to switch from one plan to the other as the situation demands. The selected plan at each junction may change automatically at different times of day to cope with daily variations in traffic flow. For instance, if signals from the inductive loops show that a vehicle perhaps an HGV is moving slowly toward a junction, SCOOT can extend the green period to allow the vehicle to clear the junction.

On the other hand, if further data input shows that the vehicle is speeding up, the extension of green time can be automatically cancelled. In the longer term, SCOOT also accumulates traffic data at a given junction over a period of time and then amends the green times on different branches so as to minimise waiting times. Changes of the current sequencing plan at each junction are noted on the log as they come into effect. They are then obliged to cross into the other traffic lane in order to pass the obstruction.

While doing this, they might well pass over an inductive sensor, which would then indicate a vehicle apparently travelling in the opposite direction.

SCOOT software is able to recognise such a situation and ignores the misleading data. The flexibility of the system is such that it can receive input from the emergency services. The emergency vehicles are thus given priority on their way to the fire. If the crossing detector shows that a person is a slow walker, the green time on the crossing is automatically extended.

Motorists at crossings benefit too. One is only too familiar with the exasperating situation of being stopped at a pedestrian crossing when there is no one wanting to cross. The pedestrian had pressed the crossing button and subsequently decided not to cross, or managed to cross during a lucky break in the traffic. The box has been opened which fact will have been noted in the log so that we can see 1 the SCOOT detector.

This one reads data from four inductive loops placed in the road at the four exits from the junction. At 2 there are the circuits for the inductive loops on the approaches to the junction. Data from 1 and 2 are relayed to the control room through the OTU, which is item 3 in the photograph.

Below, at 4 is the rack holding the processor cards of the local junction computer. Its power supply is to the right of this. Below the computer and out of sight in the photograph is the power supply for the signal lamps. These are 24V lamps and receive their supply from a transformer working on the V a.

The system incorporates a photosensor that detects low ambient light levels, such as occur at night and during overcast weather. Welcome, Guest. Please login or register. Did you miss your activation email? This topic This board Entire forum Google Bing. Print Search. Pages: [ 1 ] Go Down.

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Thanks for that, I will leave it alone. Fraser Super Contributor Posts: Country:. I know them quite well.