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Alarm-higgered telephone dialler This automatic telephone dialler can be added to any home burglar alarm system. If someone breaks in and triggers the alarm, the dialler will call a pre-determined number and transmit a beeping tone. By GREG SWAIN Many people have installed burglar alarms in their homes but not too many have bothered to add an automatic telephone dialler to their system. The main reason for this in the past has been the cost automatic telephone diallers can be expensive. Even so, an alarm triggered dialler is a good idea. By dialling a pre-determined number, it can immediately alert the owner or a third party if the alarm is triggered. All the owner has to do is enter in the number to be dialled before leaving the house. The other advantage of a dialler is that you can have a 'silent' alarm; ie, one that doesn't set off a siren. Instead of blasting the neighbourhood, the alarm can be used to dial a neighbour who can then check things out. Most sirens tend to be ignored (or cursed) by neighbours anyway, particularly if a system has been known to false trigger. Of course, use of the dialler doesn't stop you from also having a siren if that's what you want. At least it could be argued that a siren might scare the thief away. OK, so diallers are a good idea but can the cost be brought down to a reasonable level? Recently, the SEPTEMBER1989 27 R&D Department at Dick Smith Electronics decided to take a look at this situation. The result is the 'Alarm Phone Dialler' presented here. To keep costs down, DSE built their dialler around a low-cost pushbutton telephone with an automatic redial facility. This is connected to some fairly simple logic circuitry housed in a separate case to produce a complete alarm triggered dialler for just $79.95. That's about half the cost of the PARTS LIST 1 pushbutton telephone, DSE Cat. F5260-68 1 PC board, code ZA-1430 1 plastic zippy box, 1 50 x 90 x 50mm 3 1 2V SPOT relays 2 momentary contact pushbutton switches 1 battery snap connector 1 3-pin DIN socket & plug 1 2 .5mm DC power socket 1 9V DC plugpack supply 1 9 solder pins 4 9mm spacers 6 4BA x 1 5mm screws 6 4BA nuts 8 4BA washers 1 length of 8-way cable Semiconductors 2 7 4C 1 4 hex inverter (IC 1 , IC3) 1 4011 quad NANO gate (IC2) 2 TIL 126 (or equivalent) optocouplers (IC4 , ICS) 1 BC547 NPN transistor (01) 3 BC557 PNP transistors (02 , 03, 04) 1 red LED (D1) 19 1 N914 diodes D2-D18, D21 , D22 2 1 N4002 diodes (D19 , D20) Capacitors 1 1 5 1 1 00µF 35VW LL electrolytic 33µF 35VW PC electrolytic 1 0µF 25VW PC electrolytic 1µF 250VAC metallised polyester 1 0.33µF metallised polyester 4 .01 µF metallised polyester Resistors (0.25W, 5%) 3 2 1 8 28 1MO 470k0 220k0 100k0 3 18k0 2 10k0 3 1k0 SILICON CHIP commercial units. In practice, the logic circuit is used to take the telephone "off hook" and trigger the automatic redial facility. Well, that's basically how it works but there is quite a bit more to it than that, as we shall see. So, if you are out, you can call home and check whether or not your alarm system has been activated. If there's no answer, it means that everything is OK (either that or your alarm system has been foiled). Main features How it works Most house alarm systems provide a 5-25V DC output when triggered. It is this DC output that is used to trigger the logic circuitry in the dialler. After that, it's quite straightforward. Dialling is achieved by using three relays to make the relevant connections to the telephone. One relay is used as an off-hook switch (ie, it bypasses the normal hook switch in the telephone) while a second relay simulates the action of the redial key. The third relay is used only if the telephone you are using requires a 2-key sequence for last number redial. This usually applies to telephones with multiple memories. On these phones, last number redial is usually achieved by pressing the# key, followed by the Okey. At the same time that dialling takes place, the logic circuit pulses a beeper which is hidden inside the telephone handpiece. This signal is acoustically coupled to the telephone's microphone and can be readily identified by the person answering the called number. A simple delay circuit is also included in the circuit to set the overall call length. This means that the dialler automatically hangs up the phone after a preset time, whether the call has been answered or not. But that's not all the circuit can do. Once it has been triggered and made its initial call, the circuit also automatically answers incoming calls. It does this by monitoring the telephone line for ring voltages. When the ring signal is detected, the telephone is again taken offhook and the beeper activated to warn the caller that the alarm system has been triggered. Then, after a short period of time, it hangs up again. All subsequent calls are then answered in similar manner until the Reset button on the front panel is pressed. Fig.1 shows the circuit of the Alarm Triggered Phone Dialler. The first thing to note is that the telephone line is isolated from the rest of the circuit by IC4 which is a TIL126 optocoupler. This provides about 5kV of isolation between the phone line and the ring detect circuit (IC3a & IC3b). We'll come back to the ring detect circuit later on. Initially, we'll concentrate on the alarm interface circuit and the dialler logic. As previously explained, the dialler is triggered by a 5-25V signal from the alarm. This signal is applied to optocoupler IC5 and turns on the internal transistor connected between pins 5 & 4. This means that pin 5 of IC5 goes low when the alarm is triggered. NAND gates IC2c & IC2d form an RS flipflop. Normally, in the Reset state, pin 10 of IC2c is low while pin 11 of IC2d is high. Similarly, IC2b & IC2a form a second RS flipflop with pin 4 normally low and pin 3 high. Thus, all relays are off and the tone generator circuit (IClb-ICle) is disabled. When the alarm is triggered, pin 8 of IC2c and pin 6 of IC2b are pulled low. This toggles the RS flipflops to the Set condition and sets off a whole train of events. To trace these through, we'll need to look at each of the RS flipflop outputs in turn. Let's start with pin 10 of IC2c. This will now be high and thus transistor Ql turns on and lights the 'Trip' LED (Dl). At the same time, the complementary output at pin 11 will be low. This low is fed to ·one input of a diode OR gate consisting of DB, D9 and Rll. The other input to the OR gate is held high by the output of IC3b, so IC2d's low output has no further effect on the circuit at this stage. That only occurs if the IC2c/IC2d flipflop has been set and a ring voltage is detected. D10 1N914 BUZZER C10 _r--OBZ- 1 .,. 250VAC LNo--1----LINE INPUT 1~i~4 Rlg 100k ---- .,. v+ v+ R20 470k A+ INPUT FROM ALARM S1 TEST v+ Il A- 04 1N914 D14 1N914 .,. 05 1N914 v+ R16 100k RB 100k D20' 1N4002 C4 V+o-----FROM PLUGPACK C11 10 v-°"]_ 25VW! I.,. 10 25VW + + 013 1N914 T B EOC v+ VIEWED FROM BELOW I C6 + 100 35VW .,012 1N914 ALARM TRIGGERED PHONE DIALLER Fig.1: the circuit is triggered by a + 5-25V DC signal at the alarm input. When this happens, RS flipflops IC2a/IC2b & IC2c/IC2d toggle and this pulls in hook switch relay RLYl and momentarily triggers the redial relays (RLY 2 & RLY3). At the same time, the buzzer beeps to warn the called party that the alarm has triggered. If we look now at the other flipflop , pin 4 of ICZb is set high while pin 3 of ICZa is set low. This low on pin 3 does two things. First, it enables the tone generator circuit via D4 and IC1f. Second, it provides forward bias for transistor QZ which turns on and activates the hook switch relay (RLY 1). So immediately the alarm is triggered, the buzzer starts beeping and the telephone is placed on-line. We now have to get the telephone to redial and this process is initiated by the high on pin 4 of ICZb. As soon as pin 4 switches high, C4 (lOµF) begins charging via RB (lOOkn). After about one second, pin 3 of IC3e switches low and pulls the base of transistor Q3 low via C7. This forward biases Q3 which now turns on and pulls in RLYZ. RLYZ's normally open contacts are wired across the redial button (usually labelled #) on the telephone. Thus, when the contacts close, the telephone immediately begins dialling the stored number. At the same time, C7 charges via R16 and, after about one second, removes the forward bias on Q3 to turn RL YZ off again. RL Y3 is used only if two key presses are required for the redial function. R9 and C5 form a delay circuit so that pin 12 of IC1f switSEPTEMBER 1989 29 BUZZER ~~ o I ~~ • B ~ 9V B~BATTERY Dlg 4---"+--+-' HOOK SWITCH -~~ ~ , -~J •,------.,_.,._ _,,,-, '""=~ ,.-.w, ~ ~ lk :!;;;..~ ~O · V+ I 9VOC ...____ PLUGPACK I ...____ Fig.2: here's how to install the parts on the PC board. Note that the two switches (S1 & S2) and the LED (D1) are installed on the copper side of board (see text). Use PC stakes at all external wiring points and don't forget the wire link between RLY2 and D14. A- ...r-.;;;;-,. A+ ~ J , ~ C, ., - 1 ALARM .....-... INPUT I TO - ~ TELEPHONE L~~,_ PLUG 1-.._ "' \ > TO TELEPHONE LINE INPUT 0 POLYESTER CAPACITORS V- FROM PLUGPACK ~/ A+ D D D ~.... ALARM No. 1 1 4 Value IEC 1µF 1µ0 0.33µF 330n 10n .01µF EIA 105K 334K 103K RESISTORS Ii D D D D D D D No. 3 2 1 8 3 2 3 Value 1MO 470k0 220k0 100k0 18k0 10k0 1k0 ches low about 2.2s after the alarm is triggered. This then turns on Q4 and RLY3 for a period of about one second to close the contacts of the second redial key. Note that the different time constants on the inputs to inverters IC3e and IC3f are necessary to ensure correct sequencing of the redial relays. With the values shown, RL Y2 turns on about one second after the telephone is taken off-hook, with RL Y3 turning on a further 1.2 seconds later. Call length OK, so we've taken the telephone off hook and dialled the number. We now have to have some means of automatically terminating the call after a preset time otherwise the called party will not be able to dial out. 30 SILICON CHIP 4-Band Code (5%) brown black green gold yellow violet yellow gold red red yellow gold brown black yellow gold brown grey orange gold brown black orange gold brown black red gold 5-Band Code (1%) brown black black yellow brown yellow violet black orange brown red red black orange brown brown black black orange brown brown grey black red brown brown . black black red brown brown black black brown brown The circuitry to do this is quite simple and consists of RlO, C6 and IC3d. When the alarm triggers, C6 immediately begins charging via RlO. After about 45s, pin 8 of IC3d switches low and, in turn, pulls pin 1 of IC2a low via D18. As a result, the pin 3 output of IC2a switches high again which means that pin 13 of IClf is also pulled high via R14. Q2 and the buzzer both now turn off, thus releasing RLY1 and hanging up the phone. Note that the IC2a/lC2b flipflop does not completely reset until the + 12V from the alarm is turned off. When the alarm does turn off, pin 4 of IC2b immediately switches low again and C4, C5 and C6 discharge via D5, D6 & D7 respectively. Diodes D21 and D22 are there to protect Q3 and Q4 from damaging reverse base-emitter voltage spikes when pins 10 & 12 of IC3 switch high again. Ring detect circuit Although the IC2a/lC2b flipflop is automatically reset in the manner just described, the IC2c/IC2d flipflop remains in the Set condition (ie, pin 10 of IC2c high & pin 11 of IC2d low). It is left this way so that the Trip LED remains alight and so that the circuit can now respond to incoming phone calls. C10, IC4 and Dl 1 form the ring detect circuit. ClO is there to remove the DC component from the phone line while D11 protects the internal LED in IC4 from reverse voltage breakdown. IC4 provides the necessary isolation between the circuit and the phone line as discussed earlier. If a call is now received, the incoming ring signal is fed to optocoupler IC4 via C10 and pulses the internal LED on and off. This in turn pulses the internal transistor connected between pins 5 & 4 of the optocoupler. IC3a's output now delivers a train of positive-going pulses and these rapidly charge C9 (33µ,F) via D10 and R12. After a short delay, pin 4 of IC3b switches low and this low is fed to D9 which forms the other half of the D8/D9 OR gate. Since both inputs to the OR gate are now low, pin 5 of IC3c and pin 2 of IC la are also low. Dl 7 will thus be forward biased which means that both the hook switch relay and the buzzer are activated as before. Thus, when a ring voltage is detected, the telephone is automatically answered and the caller hears a beeping tone from the buzzer. R13 and C9 determine the time that the dialler stays on line after answering a call. When the phone is answered, the ring voltage ceases and pin 2 of IC3a goes low. C9 then discharges via R13 and, after about 33s, pin 4 of IC3b switches high again. Dl 7 is now reverse biased and so the buzzer stops and Q2 turns off to hang up the phone. Note that the circuit will now answer any subsequent calls in exactly the same manner. It will also redial the number if the alarm is retriggered. The dialler can only be fully reset by manually pressing the Reset button (S2). When this is done, pin 13 of IC2d is pulled low via D2 and pin 1 of IC2a is pulled low via D3. Both RS flipflops then revert to the Reset condition (assuming, of course, that there is no + 12V input from the alarm). The Test button (S1) simulates the alarm condition. When pressed, it pulls pin 8 of IC2c and pin 6 of IC2b low via Rl. The circuit then responds exactly as if a + 12V trigger signal had been received at the alarm input (ie, the buzzer sounds, the relays are activated and the dialler hangs up after 45 seconds). The buzzer circuit A simple tone generator circuit consisting of inverters ICl b & IClc is used to drive the piezo buzzer. The PC board is mounted on the lid of the case using 9mm standoffs, machine screws and nuts. Check that the two switches and the LED protrude by the correct amount through the panel before finally securing the PCB. Use cable ties to provide strain relief for the cables. The inverters are wired in a standard 2-gate configuration while R21 and C13 set the frequency of oscillation to about 800Hz. The output signal for the buzzer is taken directly from pin 6 of IClc. The tone generator does not run continuously, however. Instead, it is gated on and off by a second oscillator made up of inverters ICld and ICle. This gating oscillator controls the tone generator via D16. The way in which this works is quite simple: when pin 8 of ICld goes low, D16 is forward biased and this disables the tone generator by holding pin 3 of IClb low. The tone generator then remains off until pin 8 of ICld switches high again. R20 and C12 set the gating oscillator frequency to about 2Hz. In practice, the gating oscillator pulses the tone generator on and off at a 2Hz rate so that the buzzer emits a series of 'beeps'. The gating oscillator is itself enabled via IClf and D15. Normally, pin 12 of IClf is low, D15 is forward biased and pin 11 of ICle is held low. This means that both the gating oscillator and the tone generator will be off and no sound will be emitted from the buzzer. When the dialler is triggered by the alarm (or if it answers a call), pin 13 of IClf is pulled low via D4 or Dl 7 as previously described. Pin 12 of IClf then switches high, reverse biasing D15 and enabling the gating oscillator. Power for the circuit is derived from a 9V DC plugpack supply, with D20 providing reverse polarity protection. This is backed up by a rechargeable 9V nicad battery which supplies power via Dl 9 if the plugpack supply is removed. SEPTEMBER1989 31 This view shows how the two switches and the LED are mounted on the copper side of the PCB. Note that the flat surface on each switch body goes towards the top of the board (see also Fig.2). To gain access inside the telephone, first remove the sticker above the keyboard and undo the two self-tapping screws. The two halves of the case can then be carefully prised apart using a 5-cent piece. Resistor R3 is included so that the battery trickle charges when the plugpack supply is connected. Construction Despite the circuit complexity, this project is easy to build and get going. That's because virtually all the parts are mounted on a single PC board. This board is coded ZA-1430 and is installed in a plastic 32 SILICON CHIP zippy box measuring 150 x 90 x 50mm. Note that this project was developed by Dick Smith Electronics and will be sold by this company as a complete kit of parts. Fig.2 shows the parts layout on the PC board. Begin construction by installing the 10 wire links, then install PC stakes at all the external wiring points. Note particularly the wire link between RL Y2 and D14. The various components can now be installed on the board. The order of assembly is not important although it's a good idea to leave the relays until last. Check your work carefully as you proceed and make sure that all polarised components are correctly oriented. These include the ICs, diodes, transistors and electrolytic capacitors. When installing the transistors, push them down onto the board as far as they will comfortably go before soldering their leads. There's no need to use IC sockets but take care when installing IC2 it facAs in the opposite direction to the other ICs on the board. The two pushbutton switches (S1 & S2) are mounted on the copper side of the board (see photo). Position them so that they are about 2mm proud of the board and use a fine-tipped soldering iron to solder the leads to the pads. The flat surface on each switch body must face towards the top of the board, as shown in Fig.2. The Trip LED (Dl) is also mounted on the copper side of the board. Install the LED so that its top surface is about 12mm above the board, to ensure that it will protrude through the front panel. Don't trim the leads at this stage as you may need to adjust the height of the LED later on. That completes the PC board assembly. It can now be mounted on the back of the pre-punched front panel using the 9mm spacers supplied and secured using 15mm-long machine screws & nuts. Check to ensure that the pushbutton switches and LED protrude by the correct amount through the panel. If not, remove the board and readjust the height of these parts as necessary. Internal wiring The next step is to install the power supply and alarm input sockets. These are mounted on one side of the case (see photo) and must be positioned low down so that they clear the PC board. You will also have to drill holes to accept the 8-way cable supplied with the kit and the telephone cable. Fig.2 shows the internal wiring DSE F-526O/68 TELEPHONE BOTTOM Fig.3: here's how to wire the dialler circuit to the pushbutton telephone. The connections to the redial switch are best made at pins 4 & 16 of ICl on the telephone PCB. The hook switch is mounted on the copper side of the board. TOP GLUE BUZZER TO BOTTOM OF CASE (/) LINE INPUTS I I I JJ details-. Connect up the power input and alarm input sockets, then wire in the battery snap connector. This done, connect the 8-way cable to the hook switch, redial, buzzer and LN terminals (see also Fig.3). The telephone plug and cable is salvaged from the pushbutton telephone and is connected to the LN terminals at a later stage. Connecting the telephone Fig.3 shows how the other end of the 8-way cable is wired to the pushbutton telephone. To do this, we first have to gain access to the innards of the phone. Here's the step-by-step procedure: Step 1: remove the sticker above the keyboard and undo the two selftapping screws. Unclip the two halves of the telephone by prising them apart with a screwdriver or 5-cent piece. Step 2: affix the piezo buzzer to the bottom half of the case using epoxy adhesive. Position the buzzer between the two plastic pillars as shown in the photo. Step 3: remove the telephone cable by unsoldering the leads, then push the PC board towards the loudspeaker until it clears the two plastic clips at the bottom end. Swing the board up to expose the hook switch and connect the 01 and Kl leads from the 8-way cable to the switch terminals. Step 4: re-install the board and connect the 02 lead to pin 16 of ICl. Connect the K2 lead to pin 4 of ICl. Note: these are the redial connections. Step 5: connect the buzzer leads and the line input leads as shown in Fig.3. Step 6: enlarge the cable entry hole in the bottom of the case to take the 8-way cable. Fit a plastic cable tie to provide strain relief, then reassemble the telephone. Step 7: complete construction by TELEPHONE PLUG wiring the telephone cable to the LN terminals of the dialler board (use a plastic cable tie inside the case to provide strain relief). Testing To test the unit, simply connect the plugpack supply and press the Test button. If everything is OK, the Trip LED will light, the buzzer will immediately starting beeping and the hook switch relay (RL Y 1) will pull in. RL Y 2 will then pull in after a second or two and quickly The leads to the hook switch can be passed through a hole in the PCB and soldered to the copper pattern at the points indicated. These points are connected to the hook switch leads via the copper tracks. SEPTEMBER 1989 33 The buzzer should be glued to the bottom of the case between the two plastic pillars using epoxy adhesive. Note that it will be necessary to enlarge the cable entry hole in the case to accept the 8-way cable which runs back to the dialler circuit. release, followed by RLY 3. Now check that the circuit automatically hangs up at the end of the call period (ie, RL Y 1 should release after about 45 seconds). The Trip LED should remain alight until the Reset button is pressed. If the call period is too long, reduce the value of C6 (eg, to 82µ,F or 68µF). The ring detect function can be checked by waiting until the ~nit automatically hangs up (after it has dialled out) and then momentarily shorting pin 1 of IC3 to ground. RLYl should immediately pull in and release after about 33s. should pull in. If RL Yl doesn't pull in, check Q2. If the buzzer doesn't start, check the circuit around ICl. Q3 and Q4 can be checked by shorting pins 10 & 12 of IC3 to ground. Check that the corresponding relays momentarily turn on in each case. The RS flipflops can be checked using your digital multimeter. Apply power, press Reset and check the NAND gate (IC2) outputs. Pins 4 & 10 should be at OV while pins 3 & 11 should be close to + 9V. Now press the Test button. Pins 4 & 10 should now be at + 9V while pins 3 & 11 should now at OV. If this doesn't happen, check the circuit around IC2 for solder bridges. If pin 10 goes high but the Trip LED fails to light, try replacing Ql. The ring detect circuit is easy to troubleshoot. Initially, pins 1 & 4 of IC3 should at + 9V, while pins 2 and 3 should be at OV. If this checks out, short pin 1 of IC3 to ground and check that pin 4 goes to OV. The buzzer should now start and also RLYl should pull in. Finally, be sure to install the alarm phone dialler so that it is out of sight. If the unit is easy to find, it could well be disabled by the thief before it has had a chance to dial out. ~ Troubleshooting If the circuit fails to work as expected, go over the PC board carefully and check the component values. You should also check that all the parts are correctly oriented and that there are no solder bridges or missed solder joints on the copper side of the board. If these checks don't reveal anything, apply power and then short pin 13 of ICl to ground. The buzzer should start beeping and the RL Yl (the hook switch relay) 34 SILICON CHIP Where to buy the kit A complete kit of parts for this project is available from Dick Smith Electronics stores or by mail order from PO Box 321, North Ryde , NSW 2113. Phone (02) 888 2105. The kit comes complete & includes a pre-punched front panel, the pushbutton telephone and a 9V plugpack power supply (but no battery). The price is $79.95 plus postage charges . Quote Cat. K-8300 when ordering. Note : copyright of the PC artwork associated with this project is retained by Dick Smith Electronics.