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Ha v e y ou go t a s h e d or a boa t on a moor in g? Her e is t h e i dea l a lar m s y s t em f or i t . . . A Solar-Powered Intruder Alarm Most blokes have got a shed – or wish they had! While many people have alarms for their home and cars, a lot of valuable stuff is unprotected in garages and sheds. It needs protecting and now you can do it with this simple alarm based on a PIR sensor. It’s solar-powered so no mains supply is needed. And let’s not forget boats on moorings – they need protecting too. 28  Silicon Chip siliconchip.com.au Specifications By JOHN CLARKE Supply Voltage: 12VDC Supply Current: 3mA during exit delay; 500µA with PIR connected while armed; 2.5mA plus 10mA for siren during alarm Exit Delay: 22 seconds Entry Delay: approximately 5s to 30s adjustable Alarm Period: approximately 25s to 147s (2.5 minutes) adjustable Armed Flash Rate: approximately once per second Armed Flash Period: approximately 22ms W Main Features • • • • • • • • • Three inputs Voltage input for PIR Instant or delayed option for each input Exit delay Entry delay Low quiescent current LED indicators Battery powered Solar cell battery charging siliconchip.com.au HETHER YOU LIVE in the city or a rural area, it is likely that you have a shed with lots of valuable gear inside – tools, machinery, electronic equipment, sports stuff, maybe a boat – you get the picture. And we’ll bet that it has no protection apart from a lock on the shed door. Maybe you have thought about the problem but it was too hard and there is no mains power out there and so on. Now you can greatly improve security for all that valuable gear with our Solar-Powered Alarm. As well as utilising a PIR sensor it has two other inputs, so you can wire it up to suit your situation. Now we know that there are plenty of burglar alarms available but most are too costly and complex to suit a shed – or a boat for that matter. You don’t need multiple sectors, back to base security etc – just a simple set-up with a loud siren. As a bonus, the simplicity of a basic alarm means a lower power requirement and it becomes practical to power the system from a battery that is charged from solar cells. We have specified a PIR (passive infrared) sensor intended for use with battery equipment where low current drain is a major consideration. It operates from a 5.5-16V DC supply and its current drain is quoted at less than 100µA at 6V. We measured current drain on our sample unit to be 70µA at 6V and 73µA at 12V. When movement is detected, the current rises to 1.3mA to light its indicator LED. In its simplest form, the SolarPowered Alarm can be used with just the PIR detector. For a shed, it is best installed inside so that it is only triggered when somebody enters. For extra protection, reed switches can be added to monitor windows. If you want to build this alarm for a boat, the PIR sensor is probably not practical because sun glinting off the water could cause nuisance triggering. In this case, you would be better to rely on reed switches or a strategically placed pressure mat. Sensor triggering Sensor triggering can be instant or delayed. Delayed triggering allows you to enter the shed and switch off the alarm before it sounds. This would be applied to the PIR sensor if it monitors the entry point. Other sensors can be set for instant triggering. All told, there are three inputs on the alarm, each selectable for instant or delayed operation. However, that does not restrict the number of sensors to three. Most reed switch and doormat sensors can be connected in parallel so that any sensor that closes will trigger the alarm. Circuit details The complete circuit of the SolarPowered Alarm is shown in Fig.1. It looks a little complicated but there is not a lot in it. It employs four lowcost ICs and associated components. The three inputs are labelled Input1, Input2 and Input3. Input1 is provided specifically for the PIR detector. The output of the PIR sensor is normally 0V but when it detects movement, it goes high to +4.5V. Its output impedance is about 700kΩ, so Input 1 employs Mosfet Q1 to provide a very high input impedance. Hence, when the PIR signal goes to +4.5V, it switches on the Mosfet and its drain goes low, to 0V. Q1 controls pins 12 & 13 of IC1d, a dual-input exclusive OR (XOR) gate. Both inputs are high at +11.4V when March 2010  29 30  Silicon Chip siliconchip.com.au F1 1A 12V SOLAR PANEL 100 10M 100k 1k OFF K ON 100k G 100k POWER S1 S 100nF 100nF 100 Q1 2N7000 D 100nF 100 100 F 16V 1M 1M 1M +11.4V IC1a 7 IC1b 1 F 5 6 1 F 2 1 14 IC1d 1 F 12 13 4 3 K A A D3 D2 K K IC1: 4030B 11 A D1 100nF 2.2k DELAYED INST LINK 3 DELAYED INST LINK 2 2.2k 1 F D5 8 9 A K A K 10 D4 10k VR2 500k 1 IC3 7555 8 100k 4 A K 5 3 470k 2 1 3 K A 10nF EXIT DELAY IC4a 2 6 7 100k 14 220 F 10k VR1 500k ALARM PERIOD 22 F D7,D8: 1N4004 47 F 2 6 7 ENTRY DELAY A K 100k 100nF 1M +11.4V IC1c +11.4V D1– D6: 1N4148 DELAYED INST LINK 1 100nF 1 7 5 6 22k 5 3 IC4b 1M K 10nF 10 4 D6 11 D K A 100 F 16V G S 2N7000 2.2k IC4: 4093B 4.7 F IC4d LEDS 13 12 4 IC2 7555 8 Fig.1: the circuit is based on a 4030 quad exclusive OR gate (IC1a-IC1d), two 555 timers (IC2 & IC3) and a 4093 quad 2-input NAND gate (IC4). IC2 sets the alarm period, IC3 sets the entry delay period and IC4a sets the exit delay period. IC2 also drives the siren via MOSFET Q2. Power comes from a 12V SLA battery which is charged by a 12V solar panel. 2010 D7 CON 1 +11.4V A SOLAR POWERED SHED ALARM INPUT 3 INPUT 2 INPUT 1 (PIR INPUT) 12V SLA BATTERY SC  + CON 2 LED2 ENTRY A 9 8 G  LED3 S D A K 10 S D  LED1 EXIT/ ARMED – SIREN + Q2 IRF540N IRF540N D K  A IC4c A ALARM 4.7k G D8 K CON2 Q1 is off. When Q1 switches low, it discharges the 100nF capacitor at pin 13 via a 100Ω current limiting resistor. With pin 13 low, the 1µF capacitor at pin 12 then discharges via the series 1MΩ resistor over a period of about one second. IC1d’s output at pin 11 is high only when the inputs differ from each other. So when pin 13 is initially pulled low by Q1, pin 12 will remain high for a short period while the 1µF capacitor discharges. So pin 11 is high during the period that the 1µF capacitor at pin 12 is discharging. When Q1 switches off, the 100nF capacitor at pin 13 quickly recharges via the 100kΩ resistor to the 11.4V supply. The 1µF capacitor at pin 12 is delayed from charging due to its 1MΩ charging resistor. So again, IC1d’s output is set high for about a second. As a result, IC1d’s output produces a high-going pulse whenever Q1 is switched on or off by the PIR sensor. Inputs 2 & 3 operate in a similar way to Input 1 except that no Mosfet is used and the 100nF capacitor is discharged via the normally open (NO) sensor contacts between input and ground (0V). The 100Ω series resistor reduces peak current through the contacts to less than 120mA. We recommend using NO sensor switches because if normally closed (NC) switches are used, the 100kΩ resistor connecting to the 11.4V supply would add an additional 114µA to the overall current drain of the circuit. Triggering The three XOR gate outputs (ie, IC1a, b & d) are coupled via diodes to links which give the option of Instant and Delayed triggering. The instant option connects to pin 9 of IC1c which is normally held low by a 2.2kΩ resistor. A high signal from the output of IC1a, IC1b or IC1d will pull pin 9 high and pin 10 of IC1c will go high whenever the pin 8 input is low (which is most of the time). Hence, each time one of the XOR gate outputs goes high, pin 10 will produce a brief positive pulse of the same duration. This pulse is coupled via a 100nF capacitor to the trigger input of IC2, a CMOS 7555 wired as a monostable. This is the Alarm Period timer. It determines how long the siren sounds after the alarm has been triggered. Normally, pin 2 of IC2 is pulled siliconchip.com.au Parts List 1 PC board code, 03103101, 59 x 123mm 1 UB3 plastic utility box, 130 x 68 x 44mm 1 low-current PIR detector (IRTEC IR-530LC) (Altronics SX5306) – do not substitute 1 12V 1.3Ah or larger SLA battery (Altronics S-5075B, Jaycar SB-2480) 1 12V solar cell trickle charger with integral diode (Altronics N-0700, Jaycar MB-3501) 1 12V siren (Altronics S-6125, Jaycar LA-5258 or equivalent) 1 SPDT toggle switch (S1) Or 1 SPDT key-operated switch (Altronics S-2501 – see text) 3 IP68 cable glands PG67 type 3 3-way PC-mount screw terminals with 5mm or 5.08mm spacings 2 2-way PC mount screw terminals with 5mm or 5.08mm spacings 1 9-way pin header broken into three 3-way headers with 2.54mm pin spacing (Link1Link3) 3 PC stakes 3 jumper plugs for above headers 4 4.8mm female spade connectors 2 4.8mm male spade connectors 1 60mm length of 2mm heatshrink tubing 1 150mm length of 0.71mm tinned copper wire or 5 x 0Ω resistors 1 length of 4-core alarm cable (length is installation dependent) 2 500kΩ horizontal-mount trimpots (code 504) (VR1,VR2) 1 in-line 3AG fuse holder 1 3AG 1A fuse high via the associated 100kΩ resistor and since IC1c’s output is normally low, the 100nF capacitor will be fully charged. Then, when pin 10 of IC1c goes high momentarily, it attempts to force pin 2 of IC2 above the positive supply, because of the positive charge on the 100nF capacitor. However, diode D4 prevents this from happening and any excess voltage from the capacitor is safely limited. After the short positive pulse from IC1c, pin 2 will then be briefly pulled low via the 100nF capacitor and this sets monostable IC2 running for its Semiconductors 1 CD4030 quad Exclusive OR gate (IC1) 2 ICL7555, LMC555CN CMOS 555 timer (IC2,IC3) 1 CD4093 quad 2-input NAND gates (IC4) 1 2N7000 N-channel Mosfet (Q1) 1 IRF540 N-channel Mosfet (Q2) 6 1N4148 switching diodes (D1-D6) 2 1N4004 1A diodes (D7,D8) 2 3mm red high-efficiency LEDs (LED1,LED3) 1 3mm green high-efficiency LED (LED2) Capacitors 1 220µF 16V PC electrolytic 2 100µF 16V PC electrolytic 1 47µF 16V PC electrolytic 1 22µF 16V PC electrolytic 1 4.7µF 16V PC electrolytic 3 1µF 16V PC electrolytic 1 1µF monolithic ceramic 6 100nF MKT polyester 2 10nF MKT polyester Resistors (0.25W, 1%) 1 10MΩ 1 4.7kΩ 5 1MΩ 3 2.2kΩ 1 470kΩ 1 1kΩ 6 100kΩ 3 100Ω 1 22kΩ 1 10Ω 2 10kΩ Optional Additional Parts SPDT reed switches & magnets (Altronics S-5153, Jaycar LA-5070 or equivalent) Pressure mat (Altronics S-5184 or equivalent) predetermined alarm period. Pin 3 will go high and this will turn on Mosfet Q2 which then drives the external siren connected to CON2. LED3 is also lit, indicating an alarm condition. At the same time, the 220µF capacitor at pin 6 begins to charge via the 100kΩ resistor and 500kΩ trimpot VR1. When it reaches 2/3 the supply voltage, the timer is switched off, with pin 3 going low. At the same time, pin 7 discharges the 220µF capacitor via the 10kΩ resistor. Note that the resistors from pin 7 are connected to the pin 3 output of March 2010  31 4004 D8 + – IC3 7555 22 F VR2 10nF D5 22k – + 4148 D6 47 F – 1M 10k 100k + 4004 SIREN SOLAR PANEL 12V SLA BATTERY D7 4.7 F S1 1 F LED1 470k I LED2 CON2 4148 100k I D D LED3 IC4 4093B 1M 1M 100nF D3 4148 220 F LINK 2 4148 100nF 10nF LINK 1 1 F 1M 1 F VR1 10 D 4148 2.2k 2.2k 1M 100 100nF 100k 1k 100nF 100k – IC2 7555 Q2 100 F 100k I 4148 IC1 4030B D2 100nF LINK 3 – + 100 INPUT 3 + 3 NI INPUT 2 10M SIG 1 F D1 100k – + – 2 NI GI S INPUT 1 CON1 100 MRALA + 10k D4 2.2k 4.7k 10130130 100nF 100 F Q1 S1 Fig.2: follow this layout diagram to install the parts on the PC board. Take care with the orientation of the polarised components and position Links 1-3 to select either instant or delayed triggering for each input. IC2 rather than the 11.4V supply. This arrangement is used to minimise current drain. Exit & entry delay An exit delay is needed so that when you power up the alarm, you have time to get out of your shed (or boat) without triggering the siren. Switch S1 powers up the alarm circuit. When power is applied, the 22µF capacitor at pins 1 & 2 of IC4a is initially discharged and this sets the output of this Schmitt NAND gate low, to hold the reset for both the IC2 and IC3 timers low. This prevents IC2 and IC3 from being triggered. The 22µF capacitor then charges via the 470kΩ resistor and after about 45 seconds or so, the voltage reaches the lower threshold for IC4a’s input and its pin 3 output goes high. Thus, pin 4 on both IC2 & IC3 goes high and both of these timers can now be triggered, ie, the alarm circuit is fully operational. IC3 is another 7555 wired as mono­ stable timer and is used for the entry delay. It is triggered if one of the links (Link1 to Link3) is set for delayed triggering. The trigger pulse for pin 2 of IC3 is coupled via a 1µF capacitor. One side of the 1µF capacitor is normally held low via a 2.2kΩ resistor to ground while the pin 2 side is held high via a 1MΩ resistor. Again, the triggering process is similar to that for IC2. When a high signal is applied from one of the diodes, D1, D2 or D3, the 1µF capacitor discharges via the now forward-biased diode D5. When the delayed signal side of the capacitor goes low, the pin 2 input to IC2 is pulled low to trigger the timer. The pin 3 output of IC3 will then go high for the entry delay period which is set by trimpot VR2. This holds the pin 8 input of IC1c high and this prevents IC2 from being triggered. The entry delay can be set anywhere between five seconds and 30 seconds. Let’s clarify a point here. When we talk about Entry Delay, we are referring to the delay which is available when any of the three input sensors closes, provided that Delayed Triggering has been selected by the link options provided by Link 1, 2 or 3 (or any combination of the three). LED indicators During the exit delay period, pin 5 of Schmitt NAND gate IC4b is held low and its pin 4 output remains high. IC4c inverts this high and so its output at pin 10 is low. Pin 3 of IC3 is low (since IC3 is currently disabled) and so pin 11 of inverter IC4d is high. The combination of pin 11 being high and pin 10 being low means that LED1 Table 1: Resistor Colour Codes o o o o o o o o o o o o No.   1   5   1   6   1   2   1   3   1   3   1 32  Silicon Chip Value 10MΩ 1MΩ 470kΩ 100kΩ 22kΩ 10kΩ 4.7kΩ 2.2kΩ 1kΩ 100Ω 10Ω 4-Band Code (1%) brown black blue brown brown black green brown yellow violet yellow brown brown black yellow brown red red orange brown brown black orange brown yellow violet red brown red red red brown brown black red brown brown black brown brown brown black black brown 5-Band Code (1%) brown black black green brown brown black black yellow brown yellow violet black orange brown brown black black orange brown red red black red brown brown black black red brown yellow violet black brown brown red red black brown brown brown black black brown brown brown black black black brown brown black black gold brown siliconchip.com.au This is the view inside the completed prototype. Note that you will have to make the wiring connections to the screw terminal blocks before sliding the PC board into the case and installing the cable clamps. is lit continuously for a period of 45 seconds which is the Exit Delay. After the Exit Delay period, the pin 3 output of IC4a allows normal operation for timers IC2 and IC3. It also allows the oscillator based on IC4b to operate by pulling pin 5 high. This now flashes LED1 at about once every two seconds. The duty cycle of the oscillator is only about 2% so while the flashing of LED1 is highly visible, the overall LED current drain is very low. During the entry delay period, IC4d’s output at pin 11 is low so LED1 is off and green LED2 is on, but not continuously. This is because the oscillator based on IC4b is still running and LED2 turns off very briefly every two seconds. At the end of the Entry Delay period, IC3’s output (pin 3) goes low again and pin 11 of IC4d goes high. This causes LED1 to flash again and the alarm will sound, since IC2 has been enabled. This lights LED3 and sounds the siren siliconchip.com.au connected to Mosfet Q2. Of course, if the Entry Delay was triggered by you, entering in a legitimate way, you will have had time to turn off the alarm and the neighbourhood will not be disturbed. Construction The Solar-Powered Alarm is constructed on a PC board coded 03103101 and measuring 59 x 123mm. This PC board is designed to clip into the integral mounting clips inside a UB3 plastic case. Fig.2 shows the assembly details. Begin construction by checking the PC board for breaks in the tracks or shorts between tracks and pads. Repair these if necessary. Check also that the hole sizes are correct for each component. The screw terminal holes are 1.25mm in diameter compared to the 0.9mm holes for the ICs, resistors and diodes. Assembly can begin by inserting the links, diodes and resistors. We used 0Ω resistors in place of wire links al- Table 2: Capacitor Codes Value µF Value IEC Code 1µF 1µF 1u0 100nF 0.1µF 100n 10n .01µF 10n EIA Code 105 104 103 though tinned copper wire links could be used instead. When inserting the resistors, use the resistor colour code table to help in reading the resistor values. A digital multimeter can also be used to measure each value. The diodes can be installed next and these must be mounted with the orientation as shown. The four ICs can then be mounted directly on the PC board or using sockets. DIP14 IC sockets are required for both IC1 and IC4 and DIP8 sockets for IC2 & IC3. Ensure that each IC is placed in its correct position and is oriented correctly with its notch or pin 1 indicating dot oriented as shown. The two trimMarch 2010  33 14 A 5 A 5 A 21 B 20 (BOX LID) CL CL 6 6 12.5 HOLES A: 3.0mm DIA. HOLE B: 6.5mm DIA 6 12.5 12.5 12.5 12 ALL DIMENSIONS ARE IN MILLIMETRES (BOX END) 12.5 12 (BOX END) Fig.3: this diagram shows the drilling details for the lid and the two ends of the case. The larger holes (ie, >3mm) are best made by first using a small pilot drill and then carefully enlarging them to the correct size using a tapered reamer. pots can now be mounted, followed by Mosfets Q1 and Q2, taking care with their orientation. The multi-way screw terminals can then go in, noting that the 7-way terminals are made using one 3-way and two 2-way sections. The 6-way terminals are made using two 3-way sections. The three LEDs are mounted with the top of each LED 28mm above the PC board. Take care with orientation. The anode has the longer lead. Follow with the capacitors, ensuring that the electrolytic types are oriented correctly. Finally, insert and mount the three 3-way pin headers and the three PC stakes. As mentioned, the PC board is designed to clip into the integral side clips within the box. The box requires holes to be drilled in each end for the cable glands. Note that there are also 6mm slots cut from the top edge of the box to the cable gland holes. These are there to make assembly possible, but more on this later. Holes are also 34  Silicon Chip required in the lid for the LEDs and power switch. Fig.3 shows the dimensions for these. Wiring The wiring for the switch and siren is shown in Fig.2. The switch wiring is soldered to PC stakes on the board and the connections covered with a 10mm length of heatshrink tubing to prevent them from breaking. The external siren is connected to the screw terminals. Testing To test the unit, connect a 12V supply to the “+” and “-” terminals on the PC board, apply power and check that LED1 lights. If LED2 lights instead of LED1, then the orientation of LED2 is reversed. If neither LED lights, check LED1’s orientation. The length of time LED1 stays fully lit is the Exit Delay period. This delay is not critical but it does need to be sufficient to allow an easy exit from the shed after switching on the alarm without setting it off. You can change the exit period by changing the capacitor value at pins 1 & 2 of IC4a. A smaller value will reduce the period while a larger value will give a longer period. Select each input for either instant or delayed triggering using the jumper pin option for each input. Note that an input will be disabled if there is no jumper connection. When red LED1 begins to flash, the alarm is ready to be triggered. Connect a wire between the two contacts for input 2. For an instant alarm selection, red LED3 should immediately light. For a delayed selection, green LED2 should light. When LED2 extinguishes, LED3 should light. If the siren is connected, it will also sound but due to its loudness, you may wish to disconnect this during testing. Alternatively, you could connect a piezo sounder instead. The Alarm Period can be set with trimpot VR1. Clockwise rotation insiliconchip.com.au (ALARM PC BOARD) 4148 I N S 4004 3 NI 4148 IN-LINE FUSE HOLDER (1A FUSE) NO COM NO COM NO COM N S + – (ADDITIONAL SWITCH) – MAGNET MAGNET MAGNET S D SOLAR BATTERY CHARGER PANEL 4148 D I N + – D 4148 REED SWITCH (EG, ALTRONICS S5153) 4004 I 4148 MRALA + – 2 NI GI S PIR DETECTOR (EG, ALTRONICS SX5306) 4148 10130130 + – S + 12V SLA BATTERY Fig.4: the PIR detector and reed switch sensors are connected to the PC board as shown here. Not shown are the connections to the siren and the on/off switch. Be sure to use a 1A fuse in series with the battery supply. creases the period while anticlockwise rotation reduces the period. The Alarm Period only needs to be long enough to attract your attention to the fact that there may be an intruder. An extra long alarm period is not necessary. The Entry Delay period is set using trimpot VR2. This period should be as short as possible but still provide sufficient time for you to gain entry to the shed to switch off the alarm. Final adjustment will be best done after the alarm system is installed in the shed (or boat). Installation Wiring for the Solar-Powered Alarm is dependent on the installation. It depends on the number of sensors used and the distance between the sensors. Wire lengths are also dependent on the location of the battery and the solar cell in relation to the alarm unit. The solar panel should be mounted on the roof of the shed and in Australia should be set facing north. Northern Hemisphere installations will have the solar cell unit facing south. Inclination should be roughly 23° up from horizontal for NSW. Higher angles are required for areas south of NSW, while lower angles are required for northern Australia. However, the actual inclination is not critical. Provided it’s in the ballpark, the solar cell output will be more than adequate to keep the SLA battery charged unless the alarm is repetitively activated each day. Decide on the type of sensor you will use with the alarm. Typically, a reed switch and magnet are used to monisiliconchip.com.au A PIR detector and some SPDT reed switches make ideal sensors for the Solar-Powered Alarm. Fig.4 shows how they are connected. tor a door or window. The magnet is installed on the moving part and the reed switch mounted on the fixed part. The normally open (NO) contacts of SPDT reed switches should be used, to provide a lower current drain from the battery. These contacts are open when the magnet is close to the reed switch but close as the magnet moves away from the reed switch. The NO contacts can be connected in parallel so that more than one window or door can be monitored on one input. However, the door entry reed switch should be connected to a different input than the window sensors, so that the window inputs can be set to an instant alarm. The door entry is normally set for a delayed alarm to allow entry into the shed to switch the unit off. The PIR sensor should be mounted so that it covers as much of the shed as possible. You can test coverage by connecting a 12V supply to the PIR detector, temporarily mounting it in March 2010  35 INNER NUT OF CABLE GLAND CABLE CABLE GLAND INNER NUT OF CABLE GLAND NOW THREADED ON INSIDE OF GLAND FERRULE CABLE GLAND'S OUTER CABLE CLAMP NUT (LOOSEN) CABLE GLAND TERMINAL BLOCK 6mm WIDE SLOT CIRCULAR HOLE FOR GLAND PC BOARD END OF BOX A SEPARATE INNER NUT FROM BODY OF CABLE GLAND, SLIDE CABLE DOWN THROUGH SLOT AND THEN PUSH GLAND BODY IN THROUGH CIRCULAR HOLE OUTER CABLE CLAMP NUT OF GLAND (TIGHTEN LAST) B THREAD INNER NUT ON CABLE GLAND FERRULE AND TIGHTEN TO SECURE IN POSITION. THEN TIGHTEN OUTER CLAMP NUT. Fig.5: the cable glands are slid into the case slots and secured after the leads have been secured to the screw-terminal blocks, as shown here. Note that the outer cable clamp nut is tightened last. Below left is the completed prototype. You can either use a toggle switch for power on/off or a remotely mounted key switch (see text). position and watching the detector LED light as you move around the shed. Note that while we used a toggle switch on the Solar-Powered Alarm to switch it on and off, an SPDT key switch could be used instead. This key switch could then be mounted outside near the door of the shed, so that the alarm can be switched on and off from outside the shed. Suitable key switches are available from Altronics (Cat. S-2501). Alternatively, you could use a DPST key switch such as the 36  S 36 Silicon Chip Altronics S-2520. However, note that you must convert it to a SPDT switch by connecting its two common terminals together. Using a key switch allows the entry delay to be set to a very short period or set to instant. Note, however, that the Exit Delay needs to be at least a second to ensure that the Solar-Powered Alarm is reset properly at power up. The Exit Delay capacitor should therefore be at least 2.2µF. The external siren should be mounted high in an inaccessible position and the wiring to it hidden so that is can siliconchip.com.au At right is another view inside the completed prototype. We used 0Ω resistors for the links but you can use tinned copper wire instead. The Altronics N-0700 12V solar-cell trickle charger includes an integral diode and is used to keep the 12V SLA battery topped up. At right is the full-size front-panel artwork (also available on the SILICON CHIP website). not be cut. Suitable sirens are available from Altronics, such as the Cat. S-6117, S-5415 or S-6120A. External wiring The wiring for the battery, solar cell and trigger inputs is shown in Fig.4. This wiring can be done with the PC board out of its box and with just the wiring passing through the cable glands. The glands are not secured into the box until later. Wiring for the PIR uses 4-core cable and this is passed through its own cable gland. One of the wires is not used and is cut short. Another cable gland is for the Input2 and Input3 cabling and this also uses 4-core cable. 4-core cable is also used for the to the battery and solar cell. Use an siliconchip.com.au in-line fuse holder for the positive battery connection. The battery wires are secured to 4.8mm female spade connectors using a crimp tool. These connectors plug into the spade battery terminals. The solar-cell charger is supplied with a lighter plug on the end of its lead. This can be cut off and 4.8mm female spade connectors attached instead. These can then go to male spade connectors that are attached to the solar cell leads from the alarm unit. When assembling the Solar-Powered Alarm into its box, firstly clip the PC board into the box and place each cable gland securing nut inside the box and the gland on the outside of the box. Pass the cable wires through the slots as shown in Fig.5. Tighten the gland to the box against its nut and then clamp the cable in place with the SC cable clamp. SILICON CHIP Solar-Powered Alarm Power Armed Alarm + + + + On Entry Delay March 2010  37