Fullscreen HTML5Med Res (??MB)HTML4

Keep tabs on your car or boat with this UHF RADIO ALARM PAGER This UHF alarm pager is ideal for keeping tabs on a boat that’s moored near your home, or on a car parked in your driveway or in a nearby carpark. When triggered, it transmits a signal that activates a buzzer in a small receiver unit. By BRANCO JUSTIC Car and boat theft is a common problem but unfortunately conventional alarm systems are not always the complete answer. You don’t have to be too far away from the vehicle to be out of earshot and, of course, most people ignore alarms due to the high incidence of false triggering. That’s the main problem with conventional alarms. Despite the fact that the car (or boat) is not far away, it’s quite possible to miss the alarm if it goes off. This particularly applies if the car is parked in the street and you live at the back of a block of units, or 36  Silicon Chip if you visit an office block or shopping centre and the car is in an adjacent car­park. This unit overcomes that problem by paging you if it de­tects an intrusion, although any such incident should always be investigated with due discretion. It has a range of about 300 metres in open air and about 150 metres in a built-up area or if you are inside a building. Note that these figures were obtained with the transmitter placed on the dashboard of a car and will vary depending on the individual installation. As can be seen from the photos, the Alarm Pager consists of two separate units: (1) a PC board which carries the sensor/transmitter circuitry; and (2) a compact receiver unit built into a plastic case with a keypad. The transmitter board mounts inside the car (or boat) and is powered by the existing 12V supply. It’s designed to be au­tomatically armed when the ignition is switched off, which means that you cannot forget to switch the unit on. It has two sensor input channels and can be triggered using vibration detectors (ie, piezoelectric transducers), high or low-going alarm sensors (eg, reed switches), or a combination of both. The receiver circuit is built into a small plastic case which is fitted with a clip so that the unit can be worn on a belt. It is controlled by a keypad which has the following func­ tions: Off, On, Battery Test (Batt.), Test and Reset. This unit is powered from a 9V alkaline battery which should have a life of about 400 hours. When a valid paging signal is received from the transmit­ter, a buzzer inside the receiver briefly “beeps” every five seconds or so and continues until the receiver is manually reset (by pushing the Reset button). This internal buzzer also provides audible feedback when the other keys are pressed. For example, pressing the On key gives a short “beep”, while pressing the Off key gives a much longer “beep”. Pressing the Test key gives the paging sequence (ie, a brief beep every five seconds), while a continuous “beep” results if the Batt key is held down (provided of course that the battery is OK). By making some simple decisions during construction, you can customise the alarm pager to suit your requirements. One option is to use the unit with an existing alarm system, so that it is triggered by an existing sensor. It could even be switched on and off using the existing alarm’s remote control. However, for the purposes of this article, we’ll assume that you intend arming it via the ignition switch. Vibration sensor Ideally, we recommend that you trigger the unit using sen­sors mounted inside the front doors or adjacent to the door pillars. A vibration detector consists of a piezoelectric disc with a threaded rod and nut assembly soldered close to the rim – see photo. This arrangement provides excellent sensitivity to bumps and knocks but, since the resonant frequency is set to about 70Hz, avoids false triggering due to low-frequency vibra­tions (eg, from wind gusts). By using this arrangement, the unit pages you each time you get out of the car and shut the door (assuming that you are using the ignition to activate the unit). The resulting sequence of beeps from the receiver assures you that the unit is working correctly and is a useful test feature. Similarly, the unit will page you when you enter the car but will be disarmed as soon as the ignition is turned on. How it works: transmitter Fig.1 shows a block diagram of the alarm/transmitter cir­ cuit. It’s really several circuits all rolled into one. Starting at the left, the alarm in- ENABLE/ DISABLE (IGNITION SWITCH) ANTENNA SWITCHED MODE +15V TRANSMITTER +15V SUPPLY IC4, Q8 IC2 SENSOR INPUT 1 SENSOR INPUT 2 P1 ALARM INPUTS 8-SECOND MONOSTABLE Q1-Q3 IC1c IC1d Q7 PT VIBRATION SENSORS Fig.1: block diagram of the UHF Alarm Pager. When an input is detected, an 8-second monostable turns on Q7 via IC1d & starts a switched mode power supply (IC2). This in turn “fires” up the transmitter circuit (IC4 & Q8). puts can be triggered by the above­ mentioned vibration detectors or by some other sensor with a pulsed output (either positive or negative-going). When triggered, the input circuit (Q1-Q3) triggers an 8-second mono­ stable and Q7 turns on (via IC1d) for the duration of the mono­stable period. When Q7 turns on, a switched mode power supply (IC2) “fires up” and supplies power to the transmitter circuit (IC4 & Q8). As a result, the transmitter broadcasts a pulse-coded RF signal for eight seconds and this signal is picked by the receiver and processed to pulse the internal buzzer on and off. Fig.2 shows the complete circuit details for the alarm/transmitter. It uses two virtually identical input chan­nels, one for low-going sensors (Input 1) and one for high-going sensors (Input 2). The only real difference between the two channels is that Input 1 includes inverter stage IC1a to invert the low-going input • pulse. Associated with this is an extra clamping diode to protect the inverter inputs (pins 1 & 2) plus a 47kΩ pullup resistor. Let’s take a closer look at how this input operates. Normally, no signal is applied to the input and so pins 1 & 2 of IC1a are pulled high. Pin 3 of IC1a will thus be low and FET Q1 and transistors Q2 & Q3 will all be off. However, when a low-going pulse is applied to the input, pin 3 of IC1a switches high and forward biases D4. As a result, a voltage of about 0.6V appears across D4 and a sample of this is applied to the gate of FET Q1 via VR1. Alternatively, the signal for FET Q1 can come from piezo transducer P1. When this vibrates (eg, when a door closes), it generates an AC output voltage. This voltage is clipped to about 0.6V p-p by back-to-back diodes D4 & D5 and applied to the gate of Q1 via VR1 as before. Features Function: detects intrusion into parked vehicles, moored boats or a building and transmits a paging signal to a receiver. • Range: approximately 300 metres in open air, reliable 150-metre range in normal building locations. Note: these figures were obtained with the transmitter placed on top of a plastic car dashboard. • Transmitter power supply: 9-14V DC operation from a car bat­tery, a plugpack supply or from a battery pack (eg, about 800 hours from eight series C-size alkaline batteries). Current consump­tion is 3.5mA quiescent or 50mA during transmission. • Receiver power supply: 9V battery (about 100 hours from a zinc-carbon battery or 400 hours from an alkaline type). Current consumption negligible when “off” or about 2.5mA when “on”. • Battery test: battery checks as OK if above 5.4V. During this test, the battery is continuously loaded by the buzzer. November 1994  37 38  Silicon Chip R11 10k D8 1N914 D2 1N914 R1 10k D1 1N914 ZD1 15V 1 2 7 R12 10k P2 PIEZO TRANSDUCER D9 1N914 OUT C13 .0033 D10 D5 D3 1N914 R3 10k +8V GND IC1a 4093 14 3 P1 PIEZO TRANSDUCER R2 47k C12 470 16VW IN IC3 7808 D11 2x1N914 D4 2x1N914 C14 10 VR2 1M VR1 1M C9 0.47 R30 220  5 C4 10 C3 680pF C2 10 C1 680pF +8V C7 100 UHF ALARM PAGER-TRANSMITTER SENSOR INPUT 2 SENSOR INPUT 1 GND FROM BATTERY +12V R31 D20 1N4007 22  1W G G 6 R14 680k R13 39k S D S Q4 2N5484 D12 1N914 D6 1N914 Q1 2N5484 C8 .0015 2.2k R28 D R4 39k 2 R5 680k 4 7 R27 470  IC2 MC34063 R26 1 3 8 1 E C11 0.47 R9 22k R10 100k R35 10k 13 R34 10k 12 R33 10k 11 R32 10k 10 R17 100k R16 2.2k R15 470  R8 100k C E B Q5 BC558 R18 22k E Q6 BC548 C R19 100k D13 1N914 E Q2 D7 BC558 1N914 C Q3 R7 BC548 C 2.2k B B R6 470  C10 100 D19 SR103 L1 +15V 5 6 A12 15 16 17 R36 1M 4 E R20 100k D14 1N914 I GO +8V IC1b R25 1k B 12 13 C5 11 10 D18 1N914 D15 1N914 C G S D VIEWED FROM BELOW C E BC--B R24 10k ICId C E B A 10 +8V C18 6.8pF C16 4.7pF 2SC3355 8 9 Q8 2SC3355 VC1 2-7pF R22 1M E C R21 10k R40 82  B * L2 *ETCHED ON PC BOARD C6 100 IC1c D16 1N914 C15 .001 C17 .001 * ANTENNA D17 1N914 R39 2.2k R37 6.8k D47 1N4148 LED1  K ENABLE/DISABLE VIA IGNITION SWITCH 9 IC4 AX5026 A11 A10 A9 18 A R38 120  K Q7 2N2219 R23 1k B R29 10  304MHz SAW FILTER E C The FET amplifier stage (Q1) is normally biased at close to its cutoff point due to the high value of source resistance used (R5 = 680kΩ). Similarly, transistor Q2 is normally biased off by R4 and so Q2’s collector normally sits at 0V. However, when a sensor is triggered (or vibrations are detected), Q1 conducts and charges capacitor C2. While C2 charg­es, sufficient base current flows to turn Q2 on and this, in turn, switches Q3 on and pulls pin 6 of IC1b low via D7 (note: pin 6 of IC1b is normally held high via R10). Q2 then switches off again as soon as C2 is charged, since the voltage across R4 is now too low to provide sufficient forward bias. IC1c and its associated parts form the 8-second mono­stable. Normally, pins 12 & 13 of IC1c are held low via R20 and so both sides of C5 are high, pin 10 of IC1d is low and Q7 is off. However, when pin 6 of IC1b goes low, its output at pin 4 switches high and pulls pins 12 & 13 of IC1c high via D14 Pin 11 of IC1c now switches low and so the positive side of C5 also goes low. Pin 10 of IC1d thus switches high and this turns on Q7 and the transmitter (by switching on its power sup­ply), as described previously. At the same time, D15 latches pins 12 & 13 of IC1c high to ensure the correct monostable timing period. C5 now charges via R22 and R21 and, after about eight sec­onds, pulls the inputs of IC1d high again. Pin 10 of IC1d thus switches low again and Q7 turns off. At the same time, the high on pins 12 & 13 of IC1c is released and so the monostable is ready for a new timing cycle. Note that when pin 10 of IC1d switches high (to turn on Q7), C6 charges via R24 and D18 and the voltage across C2 is pulled high via D6. Similarly, the voltage across C4 Fig.2 (left): this diagram shows the complete circuit details for the alarm/ transmitter. It uses two virtually identical input chan­nels, one for low-going sensors (Input 1) and one for high-going sensors (Input 2). When triggered, Q7 turns on & the transmitter section (IC4 & Q8) broadcasts a coded RF signal, as set by address lines A9-A12. The pre-built UHF front-end module in the receiver must be installed with its component side towards the AX528 decoder IC, as shown here. Sockets were used to mount the ICs in the prototype but these can be considered optional. in the other channel is held high via D12. This effectively disables the two input channels during the 8-second monostable period and for some time afterwards since FETs Q1 & Q2 are biased off. When pin 10 of IC1d switches low, it takes about 30 seconds for C6 to discharge via R5 & R14. This means that the 8-second monostable can only be retriggered some 30 seconds after the previous cycle has ended. This prevents false triggering at the end of the monostable period. The other sensor input channel accepts signals from sensor 2 and/or piezo transducer P2. As mentioned previously, it works in virtually identical fashion. When triggered, Q6 pulls pin 5 of IC1b low and so pin 4 swit­ ches high and triggers the 8-second monostable as before. IC2 and its associated parts forms the switched mode power supply. This is enabled whenever Q7 is on (ie, during the 8-second monostable period) and supplies power to the transmitter circuit. IC2 is an MC34063A DC-DC converter IC and is wired here in standard step-up configuration. It accepts an 8V input from 3-terminal regulator IC3 and steps this up to provide an output of 15V across C10. R28 & R30 set the output voltage, while C8 sets the frequency of the internal switching oscillator. This arrangement is used to provide a stable +15V supply rail for the transmitter. It ensures frequency stability with varying input supply voltages and also ensures that the transmit­ter board can be used with supply voltages from 10-14V. Transmitter circuit The transmitter circuit is based on an AX-5026 trinary encoder IC. When power is applied, this IC generates a sequence of pulses at its output (pin 17). The rate at which these pulses are generated is set by a 1MΩ timing resistor (R36), while the code sequence is set by resistors R32-R35. These resistors pull the A9-A12 address lines low, while the remaining address lines are left open circuit. The coded output from IC1 appears at pin 17 and drives RF transistor Q8. This transistor is connected as a Hartley oscilla­tor operating at 304MHz, as set by a tank circuit consisting of L2 (etched on the PC board), VC1, C16 and C18. In addition, a SAW resonator is used to provide a narrow-band feedback path. Its lowest impedance is at its resonant frequency of 304MHz and thus the tuned collector load must be set to this frequency in order for Q8 to oscillate. The SAW resonator ensures frequency stability and makes the transmitter easy to align. It ensures that the oscillator will only start and pulse LED 1 when the tuned circuit is virtually dead on frequency. November 1994  39 ON S5 7 IC3d K BATTERY TEST S3 R15 27k K  R8 47k D1 1N914 R7 470k 11 C3 22 8 10 1,3,6,8 10,11,12 UHF ALARM PAGER-RECEIVER TEST E S1 A12 12 A11 A10 A9 11 10 9 R4 4.7k 2 Q1 BC548 C B UHF RECEIVER MODULE 2 7 5 R2 1M 16 13 IC1 AX5028 17 R3 10k C1 0.47 18 14 15 R1 220  1 11 RESET S2 13 IC3b 12 9 11 4 3 CONNECTION NUMBERS ON SWITCHES REFER TO KEYPAD HEADER SOCKET LED2 R11 4.7k A BUZZER 7 R10 14 4.7k 10 IC2d 4093 9 IC3a 4093 8 R6 4.7k R5 4.7k IC2c IC2a 1 Fig.3: the coded signal from the transmitter is processed by the UHF front-end module & decoded by IC1. When a valid signal is received, Q1 turns on & oscillator stage IC2a drives Q2, the buzzer & LED 2 to deliver the paging signal. C E 7 R14 10k R13 10k A Q2 BC558 E LED1  R12 B 22k K E C Q3 B BC558 C R9 10k C4 0.47 C2 22 13 6 12 5 2 IC2b 4093 ANTENNA 40  Silicon Chip VIEWED FROM BELOW B D5 1N914 D4 1N914 D3 1N914 D2 1N914 +9V R17 1k R16 1k A C5 22 C6 100 4 IC3c 4093 3 How it works – receiver 6 12 0FF S4 5 2 1 14 R18 4.7k R19 4.7k 4 B1 9V VC1 is used to adjust the centre frequency of the tuned circuit. This point corresponds to maximum current consumption and is found by adjusting VC1 to obtain peak brightness from the LED 1. Fig.3 shows the circuit details of the receiver. This is based on a factory-built “front-end” module that’s accurately aligned to the transmitter frequency (304MHz). It uses surface mount components to give a compact assembly and is fitted with a pin connector along one edge so that it can be plugged into a PC board. In operation, the front-end module picks up the coded RF pulses from the transmitter via a short antenna. The received signal is then processed via an internal bandpass filter, an RF preamplifier, a regenerative detector, an amplifier and a Schmitt trigger. When a valid signal is received, a digital pulse train appears at pin 5 and this is fed to pin 14 of IC1. IC1 is an AX-528 Tristate decoder and is used to decode the signal generated by the transmitter. As with the AX-5026 encoder, this device has 12 address lines (A1-A12) and these are connected to match the transmitter code (ie, pins 10-13 are all pulled low). If the code sequence on pin 14 of IC1 matches its address lines, the valid transmission output at pin 17 switches high and turns on transistor Q1. This in turn triggers an S-R flipflop based on gates IC3a & IC3b. Normally, the flipflop is in the reset state and so pin 10 of IC3a is low. However, when Q1 turns on, pin 8 of IC3a is pulled low and so pin 10 goes high. This high enables a Schmitt trigger oscillator stage based on IC2d. Its timing capacitor (C3) is charged via R7 each time pin 10 goes high and discharges via D1 and R8 when pin 10 goes low. This arrangement means that IC2d operates with a duty cycle of about 10:1. As a result, a pulse train that’s high for about five seconds and low for 0.5 seconds appears at pin 10 of IC2d. This pulse train is applied to the base of PNP transistor Q2 and this in turn drives the buzzer (B1) to produce a brief sound every five seconds. It also flashes LED 2 which is wired in parallel with the buzzer. Test switch S1 bypasses transistor Q1 and is used to check that the buzzer circuit is working correctly. Once the buzzer is activated, the circuit can only be reset by pressing S2. This pulls pin 13 of IC3b low and resets the S-R flipflop. The receiver circuit is turned on and off by switching power to the UHF front-end module and to decoder IC1. This is done by pressing switches S4 & S5 and these in turn toggle a second S-R flipflop based on IC3c & IC3d. When S5 (ON) is pressed, pin 6 of IC3d is pulled low and the output at pin 4 goes high and pulls pin 2 of IC3c high. Pin 3 of IC3c thus switches low and this low is inverted by parallelled inverter stages IC2a-IC2c to supply power to the UHF front-end module and to IC1. INPUT 1 ENABLEDISABLE 10uF 22k D13 100k 470  D12 2.2k 100k 39k 82  IC4 AX5026 1M Q6 Q5 1 10k .0033 100uF .001 2.2k D47 6.8k A K 120 10k D18 Q8 SAW LED1 10k D19 D6 .001 4.7pF 1 .0015 0.47 10k 2.2k 22k D7 100k 680pF 100k Q2 Q4 10k 470uF IC3 7808 D20 +12V 22  1W GND 10k D8 D9 470  39k 680 k 10uF 680k D4 D5 D11 D10 VR2 Q3 6.8pF 100uF 10k 10W 1k 1k 1M 680pF 10uF INPUT 2 D16 D17 10k D15 IC2 34063 VR1 P2 220  1 470  L1 2.2k 1 Q1 P1 VC1 Q7 D14 IC1 4093 10k 47k D2 D1 10k D3 0.47 10uF 100k ZD1 Fig.4: install the parts on the transmitter PC board as shown here, taking care to keep all component leads in the UHF transmitter section (around IC4 & Q8) as short as possible. The enable/disable input is wired to the ignition switch. Pressing S4 (OFF) has the opposite effect. This pulls pin 1 of IC3c low and so the output at pin 3 goes high. The outputs of inverters IC2a-IC2c thus switch low and remove power from the front end of the circuit. The remainder of the circuit draws negligible current in the quiescent state and so is permanently powered from the 9V battery. The RC timing circuits connected to the outputs of IC3c & IC3d set the on and off indication periods. When S5 (ON) is pressed, pin 3 of IC3c goes low and this takes the negative side of C5 low. C5 now immediately begins charging via LED 1, the base-emitter junction of Q3, R13, D3 & R16. As a result, Q3 turns on while C5 charges and briefly flashes LEDs 1 & 2 and sounds the buzzer. A similar sequence of events occurs when S4 is pressed except that this time C6 charges via R14, D5 & R17. Diodes D2 & D4 ensure that the positive sides of C5 & C6 can not rise more than 0.6V above the positive supply rail. Finally, the circuit includes a battery test feature based on S3, R12 & R15. Because of the values chosen for R12 & R15, Q3 will only be biased on when S3 is pressed if the battery voltage is greater than about 5.5V. This means TABLE 1: RESISTOR COLOUR CODES (TRANSMITTER BOARD) ❏ No. ❏   2 ❏   2 ❏   5 ❏   1 ❏   2 ❏   2 ❏ 10 ❏   1 ❏   3 ❏   3 ❏   3 ❏   1 ❏   1 ❏   1 ❏   1 ❏   1 ❏   1 Value 1MΩ 680kΩ 100kΩ 47kΩ 39kΩ 22kΩ 10kΩ 6.8kΩ 2.2kΩ 1kΩ 470Ω 220Ω 120Ω 82Ω 10Ω 1Ω 22Ω 4-Band Code (1%) brown black green brown blue grey yellow brown brown black yellow brown yellow violet orange brown orange white orange brown red red orange brown brown black orange brown blue grey red brown red red red brown brown black red brown yellow violet brown brown red red brown brown brown red brown brown grey red black brown brown black black brown brown black gold gold red red black brown 5-Band Code (1%) brown black black yellow brown blue grey black orange brown brown black black orange brown yellow violet black red brown orange white black red brown red red black red brown brown black black red brown blue grey black brown brown red red black brown brown brown black black brown brown yellow violet black black brown red red black black brown brown red black black brown grey red black gold brown brown black black gold brown brown black black silver brown red red black gold brown November 1994  41 No particular order need be followed for the transmitter board assembly but make sure RECEIVER 0.47 that all polarised parts are cor­ FRONT END 1 rectly oriented. In addition, 22uF 220  be sure to keep all component 1M leads as short as possible in the Q1 1 transmitter circuit (top right­ 0.47 IC1 AX528 hand corner of the board). 1 Note that the flat side of trimmer capacitor VC1 should go 4.7k LED1 towards Q8. The SAW resonator K A Q2 Q3 IC3 should be mounted flat against 470k 4093 47k the board, while transistor Q8 K A 1100uF 22uF D1 should only stand about 1mm LED2 22UF proud of the board. Be careful BUZZER with the orientation of the LED – its anode lead is the longer D2 D4 of the two. It can be mounted close to the PC board since it is 27k only used during the setting-up 10k procedure. 10k The large inductor (L1) is KEYPAD SOCKET B1 supplied pre-wound and can 1 be left until last. Clean and Fig.5: this is the layout for the receiver tin the ends of its leads with PC board. Note that pins 10-13 must be solder before mounting it on connected to the 0V rail via short wire the board. When this is done, links to match the address code in the check the board carefully to transmitter (see text). ensure that the assembly is correct – it only takes one wrong that the buzzer will sound and the component value to upset the circuit two LEDs will light only if the battery operation. is OK. The receiver board is equally straightforward to assemble but again Construction keep all leads as short as possible. Fig.4 shows the wiring details for Install the parts exactly as shown in the transmitter board, while Fig.5 Fig.5, leaving the receiver module till last. This component must be installed shows the receiver layout. 4.7k 22k D3 D5 1k 1k 4.7k 4.7k 4.7k 10k 4.7k IC2 4093 10k 4.7k 250mm ANTENNA The completed receiver can be fitted with a clip so that it can be worn on a belt. Note that the keys on the keypad must be labelled exactly as shown here; ie, key 1 = Reset, key 3 = Test, key 5 = Battery Test, key 7 = Off & key 9 = On. with its component side towards the 1MΩ resistor. The 13-pin keyboard connector is mounted at the other end of the board – see photo. It’s optional as to whether the two LEDs are hidden inside the case (in which case there will be no visible paging or on/off indication) or mount­ed on the end of the case near the keypad. If you elect to hide them inside the case, they can be mounted directly on the The keypad is connected into circuit by plugging it into a keypad socket at one end of the receiver PC board. Take care to ensure that the buzzer is oriented correctly & don’t forget to fit a 250mm-long antenna to the designated pad near the front-end module. 42  Silicon Chip PC board and all indication will be via the buzzer. On the other hand, you might wish to have a silent pager, with indication via the LEDs only (just leave the buzzer out). The antenna consists of a length of insulated hook-up wire about 250mm long. This is soldered to a pad which connects to pin 2 of the front end module. The A9-A12 address line of AX528 decoder IC must now be tied low to match the address programmed into the AX5026 encoder in the transmitter. This simply involves connecting pins 10-13 to the adjacent earth track that runs along the outside edge of these pins. Note: if you wish, you can alter the coding in both the transmitter and the receiver by tying selected address pins high or low or leaving them open circuit. That way you can have your own unique code, although it is not really necessary for this project. For example, you might tie A9 high, leave A10 open circuit, and tie A11 & A12 low. Short wire links can be used to make these connections in the receiver but note that you will have to scrape away the solder mask from the adjacent rails at each connection point so that the track can be soldered (the positive rail runs adjacent to the inside edge of the address pins in the receiver). What ever you do, make sure that the transmitter code exactly matches the receiver code otherwise the remote control won’t work. Once completed, the receiver board can be installed in the bottom of the case and secured to the integral standoffs using a couple of self-tapping screws. This done, plug the keypad into its connector and secure it by A piezo disc is turned into a vibration detector by soldering a threaded rod & nut assembly (made of brass) close to its rim to give a resonant frequency of about 70Hz. The opposite edge of the disc is then soldered to a piece of scrap PCB material as shown here. The wiring connection should be run using shielded cable (centre conductor to the centre of the piezo disc, shield to the PC board). peeling away its backing paper and carefully affixing it to the top of the case. The keys on the keypad should be labelled exactly as shown in the photograph; ie, key 1 = Reset, key 3 = Test, key 5 = Battery Test, key 7 = off and key 9 = on. Test & alignment To test the receiver, connect a 9V battery and carry out the following checks: (1). Press Test and check that the buzzer beeps and LED 2 flashes every five seconds or so. Check that the circuit can be reset by pressing Reset. (2). Press On and check that the buzzer briefly sounds and that both LEDs briefly light. If so, press Off and check that the buzzer sounds and both LEDs light for about three seconds. (3). Press Batt and check that the buzzer sounds and that both LEDs light for as long as the key is held down. If all these checks are OK, then most of the receiver cir­cuit is working correctly and the case assembly can be completed. Before doing this, however, a small channel must be filed in the end of the case adjacent to the battery compartment to serve as an exit point for the antenna. The case can then be clipped together and secured using two self-tapping screws at the battery compartment end. We now come to the transmitter TABLE 2: RESISTOR COLOUR CODES (RECEIVER BOARD) ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ No. 1 1 1 1 4 7 2 1 Value 1MΩ 470kΩ 47kΩ 27kΩ 10kΩ 4.7kΩ 1kΩ 220Ω 4-Band Code (1%) brown black green brown yellow violet yellow brown yellow violet orange brown red violet orange brown brown black orange brown yellow violet red brown brown black red brown red red brown brown 5-Band Code (1%) brown black black yellow brown yellow violet black orange brown yellow violet black red brown red violet black red brown brown black black red brown yellow violet black brown brown brown black black brown brown red red black black brown November 1994  43 PARTS LIST Transmitter Board 1 PC board, code OE93/ PAGERTX 1 304MHz SAW filter 1 prewound inductor (L1) 2 piezo discs 2 1MΩ trimpots Semiconductors 1 4093 quad Schmitt NAND gate (IC1) 1 MC34063 switched mode supply IC (IC2) 1 7808 3-terminal regulator (IC3) 1 AX-5026 trinary encoder (IC4) 2 2N5484 FETs (Q1,Q2) 2 BC558 PNP transistors (Q2,Q3) 2 BC548 NPN transistors (Q3,Q4) 1 2N2219 NPN transistor (Q7) 1 2SC3355 NPN RF transistor (Q8) 1 15V 1W zener diode (ZD1) 1 SR103 Shottky power diode (D19) 1 1N4007 power diode (D20) 19 1N4148 or 1N914 signal diodes (D1-D18, D47) 1 red LED (LED1) Capacitors 1 470µF 16V electrolytic 3 100µF 16V electrolytic 4 10µF 16V electrolytic 2 0.47µF monolithic 1 .0033µF ceramic (3n3) 1 .0015µF ceramic (1n5) 2 .001µF ceramic (1n) 2 680pF ceramic 1 6.8pF ceramic 1 4.7pF ceramic 1 2.7pF trimmer capacitor (VC1) Resistors (0.25W, 5%) 2 1MΩ 2 1kΩ 2 680kΩ 3 470Ω 5 100kΩ 1 220Ω 1 47kΩ 1 120Ω 2 39kΩ 1 82Ω 2 22kΩ 1 10Ω 10 10kΩ 1 1Ω 1 6.8kΩ 1 22Ω 1W 4 2.2kΩ Receiver 1 PC board, code OE/93/PAGER 1 case with battery compartment 1 keypad 1 PC-mounting keypad socket 1 304MHz front-end module 1 9V buzzer Semiconductors 1 AX-528 Tristate decoder (IC1) 2 4093 quad Schmitt NAND gates (IC2,IC3) 5 1N4148 signal diodes (D1-D5) 2 red LEDs (LED1, LED2) 1 BC548 transistor (Q1) 2 BC558 transistors (Q2,Q3) Capacitors 1 100µF 16V electrolytic 3 22µF 16V electrolytic 2 0.47µF monolithic Resistors (0.25W 5%) 1 1MΩ 4 10kΩ 1 470kΩ 7 4.7kΩ 1 47kΩ 2 1kΩ 1 27kΩ 1 220Ω Where To Buy The Parts A kit of parts for the UHF Alarm Pager is available from Oatley Electronics, PO Box 89, Oatley, NSW 2223. Phone (02) 579 4985. Prices are as follows: Transmitter (includes PC board plus on-board components): $49.00. Receiver (includes PC board, on-board components, case & keypad): $52.00. Please add $4 for postage with each order. Note: copyright © of the PC boards associated with this project is retained by Oatley Electronics. alignment. To do this, temporarily solder a link between the collector and emitter of Q7 and apply power (12V to +12V & GND). This will start the switch­mode supply based on IC2 44  Silicon Chip and “fire up” the transmitter for as long as the link is in place. All you have to do now is adjust VC1 using a plastic tool until LED 1 begins to flash. When this happens, the oscillator is working and you can tweak VC1 for maximum transmitter output (ie, maximum LED brightness). Finally, the completed transmitter board can be tested by removing the link across Q7, then re-applying power and pull­ing sensor input 1 low (ie, by connecting the input to ground). When you do this, the transmitter LED should flash for about three seconds. If the receiver is on, it should immediately begin paging you (ie, you should hear a brief beep every five seconds). Sensor input 2 can be checked in a similar manner by con­necting it to the positive supply rail. Just remember that after each transmission, you will have to wait at least 30 seconds before the transmitter can be reactivated (this is the time it takes for C6 to discharge, as described earlier). In fact, it’s best to wait for about 60 seconds after the transmitter LED goes out before attempting to retrigger the unit. Installation Finding a convenient location to mount the module is prob­ably the greatest challenge in installing the unit. On top of the rear parcel shelf is probably the best location in a car, with power derived from the supply to the boot lamp. The enable/dis­able input should be connected to the switched side of the igni­tion switch and this will involve running a lead back to the front of the vehicle (eg, you can tap into a suitable point in the fusebox). If you elect to switch the unit using a UHF remote control (eg, as part of an existing alarm), just remember that pulling the enable/disable input high (ie, to +8V) disarms the circuit. The vibration detectors can be installed inside small plastic cases and these can be mounted next to the door pillars. Finally, note that this unit can be easily adapted for use as a 12-channel paging system and that is why provision has been made on the transmitter board for diodes D21-D42 (bottom right­ hand corner). When combined with suitable switches, these diodes change the coding of the transmitter and you can build individual receivers with unique matching codes. Full details on how to convert the unit to a 12-channel pager will be supplied with a kit from Oatley Electronics and this kit will also include SC the extra diodes (D21-D42).