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Build this talking headlight reminder Ever leave your car’s headlights or parking lights on? Flatten the battery too? If so, you need this talking headlight reminder. If you accidentally leave your headlights on, it tells you to switch them off. By DARREN YATES Most headlight reminders are quite simple devices. Typical­ly, they sound a beeper if the ignition is switched off while the headlights are still on. In some cars, the beeper is not activat­ed until a door is opened but regardless of the triggering method used, a headlight reminder can save you from a great deal of inconvenience. Of course, if you drive an old car, then it’s quite prob­able that is lacks this very useful feature. This Talk- ing Head­ light Reminder is actually far more elaborate than a headlight reminder needs to be but it’s easy to build and it has one big advantage over other such units – you can record your own mes­sage. After all, what could be more attention-getting than “you’ve left yer lights on stupid”, or something equally hard hitting? The recorded message is continually replayed over a 30-second period, after which the device automatically switches itself off. The heart of the Talking Headlight Reminder is a 16-second sound recorder IC, the ISD1416 from Information Storage Devices. This is a second generation device and is based on the original ISD1016 which we used in the 16-Second Message Recorder described in July 1993. Like the original device, the ISD1416 features 16 seconds of recording time but now has the added features of optional edge-level control and automatic power down. Edge-level control simply means that playback can be initiated by momentarily press­ing the PLAY button, although that feature is not used here. Power for the circuit is supplied via the headlights switch, while the trigger input monitors the ignition switch. The sound comes from an external speaker and this can be October 1994  37 INTERNAL CLOCK XCLK MIC MIC REF AGC DECODERS AMP ANA OUT ANALOG TRANSCEIVERS ANTIALIASING FILTER ANA IN PREAMP pling rate. The signal is then sampled and stored in the EEPROM array, ready for playback. During playback, the stored samples are clocked out of the EEPROM array and passed through a 5-pole smoothing filter. The recovered signal is then fed to an internal audio amplifier and this can either drive a small loudspeaker directly or an external power amplifier. Thankfully, the circuitry inside the IC takes care of all the difficult jobs such as providing clock signals and sampling rates. All we have to do is apply the signal, make sure that the correct lines are either high or low, and that’s about it. SAMPLING CLOCK TIMING SP+ SMOOTHING FILTER SP- AMP 128K CELL NONVOLATILE ANALOG STORAGE ARRAY AGC POWER CONDITIONING VCCA VCCD ADDRESS BUFFERS DEVICE CONTROL A0 A1 A2 A3 A4 A5 A6 A7 REC PLAYE PLAYL RECLED Fig.1: this block diagram shows the main components of the ISD1416 sound recorder IC. It uses a 128K-cell EEPROM to store up to 16 seconds of audio in analog form, a technique that eliminates the need for A/D & D/A converters. mounted either under the dashboard or under a seat. OK, that’s just one application for this device. It could be used anywhere you need a solid-state message recorder that re­ p eats a recorded message over a 30-second interval. All you have to do is connect the appropriate supply voltage and trigger input. ples the incoming audio signal and stores the samples as analog voltages in a 128,000-cell EEPROM (electric­ ally erasable programmable read-only mem­ ory). This technique provides much better sound quality than can be obtained from a similar digital device and means that the recording is retained in memory when the power is removed. And because the information is stored in the EEPROM in analog form, there’s no need for A/D and D/A converters. In greater detail, the incoming audio signal is amplified and fed through a 5-pole anti-aliasing filter to remove frequen­cies greater than half the sam- Sound storage Refer now to Fig.1. This shows the block diagram of the ISD1416 and we’ll go over the principles of this chip briefly. During recording, the device sam- How it works Let’s now take a look at the circuit for the Talking Head­light Reminder –see Fig.2. As you can see, there are just three ICs involved: a 555 timer Fig.2 (below): the circuit is based on the ISD1416 sound recorder (IC2). If the ignition is switched off before the lights, IC1 turns Q1 on for 30 seconds & IC2 repeats the recorded message until the timing period ends. IC3 is the audio amplifier stage. D2 1N4004 REG1 78L05 OUT GND 1k 1k 0.1 10k RECORD LED1 0.22 A K 18 0.22 17 10 16VW MIC 24  25 PLAYE MIC MIC REF RECLED 1M 100k FROM IGNITION SWITCH 1k D1 1N4004 100k 7 6 0.1 PLAY S1 Q1 BC548 C 4 8 3 100k B REC S2 IC1 E 555 5 2 1 22 25VW 0.1 B E C E B C VIEWED FROM BELOW TALKING HEADLIGHT REMINDER 38  Silicon Chip IN CHASSIS OUT 100 16VW 1 14 1k 20 GND REG2 7809 100k 27 REC 23 AIN PLAYL 1 A0 AOUT 2 A1 3 A2 XCLK 5 A4 6 AGC A5 VSSD VSSA 12 13 V+ FROM HEADLIGHT SWITCH 100 16VW 28 VCD 16 VCA A3 4 9 A6 10 A7 IC2 SP+ ISD1416 10k IN 1 VOLUME VR1 10k 6 3 IC3 2 LM386 7 21 4.7k 10 16VW 5 4 100 8W EXT. SPKR 0.1 10  26 19 470k 4.7 25VW A K I GO I GO LED1 MIC 100k 100uF 1uF 1k REG2 100uF 0.22 IC3 LM386 1 IC2 ISD1416 0.1 TO IGNITION SWITCH 1 S1 (IC1), the ISD1416 (IC2) and an LM386 audio power amplifier (IC3). D1, IC1 and transistor Q1 form the playback trigger circuit for IC2. If the headlights are off when the ignition is switched off, nothing happens since no power is applied to the circuit. However, if the ignition is switched off first, D1 is forward biased (since its cathode is pulled low) and a short Below: the PC board is mounted on the back of the lid using 19mm long spacers & secured using machine screws & nuts. Note the method used to mount the two switches. S2 470k 1uF D1 TO SPEAKER TO SPEAKER CHASSIS 1k 100k 100k D2 +V FROM LIGHT SWITCH 0.1 4.7k 22uF 1k 100uF VR1 10  1 REG1 0.1 10k 0.22 Fig.2: install the parts on the PC board as shown here, taking care to ensure that all polarised components are correctly oriented. The two pushbutton switches (S1 & S2) are mounted by soldering their pins to the tops of PC stakes (see photo below). K 1k 10uF 0.1 IC1 555 10k Q1 100k 1M A 4.7uF negative-going pulse is applied to pin 2 (the trigger input) of IC1. IC1 is wired in monostable configuration. When triggered, its output at pin 3 goes high for approximately 30 seconds. This turns on transistor Q1 which in turn pulls the PLAYL input (pin 23) of IC2 low. PLAYL stands for “PLAY LEVEL”, which indicates that it is a level-triggered input rather than an edge-triggered one. Thus, IC2 only plays back the recorded message during the 30-second period that Q1 is on (ie, for as long as the PLAYL input is held low). Note that the address lines (A0- A5) of the ISD1416 are all connected to ground. This places the device into “loop” mode, so that the recorded message is repeatedly replayed during the 30-second period. Alternatively, IC1 (and thus IC2) can be manually triggered by pressing switch S1 (PLAY). Normally, this switch would not be used once the device is installed in a car. It’s there simply to provide a convenient way of triggering the recorded message during the setting up procedure. The audio output from IC2 appears at pin 14 and is AC-cou­pled to pin 2 of IC3, an LM386 audio amplifier. Its October 1994  39 PARTS LIST The ISD1416 sound recorder IC is mounted in an IC socket while the two remaining ICs are soldered directly to the PC board. Take care to ensure that the two switches are oriented correctly (ie, flat side to the right). 1 PC board, code 01109941, 102 x 58mm 1 plastic zippy case, 130 x 68 x 41mm 1 front-panel label 1 green snap action momentary switch (S1) 1 red snap action momentary switch (S2) 1 8-ohm 1W loudspeaker 1 electret microphone insert 1 28-pin machined IC socket 1 10kΩ 5mm trimpot (VR1) 1 5-pin 0.1-inch header 13 PC stakes 4 19mm spacers 4 3 x 30mm machine screws plus nuts & washers Semiconductors 1 NE555 timer (IC1) 1 ISD1416 16-second sound recorder (IC2) 1 LM386 low-power audio amplifier (IC3) 1 78L05 5V 100mA regulator (REG1) 1 7809 9V regulator (REG2) 1 BC548 NPN transistor (Q1) 2 1N4004 silicon diodes (D1,D2) 1 5mm red LED (LED1) Fig.4: this is the full size etching pattern for the PC board. output ap­pears at pin 5 and drives an 8-ohm loudspeaker via a 100µF ca­ pacitor. Trimpot VR1 functions as the volume control, while a Zobel network consisting of a 10Ω resistor and series 0.1µF capacitor is connected across the output of IC3 (pin 5 & GND) to ensure stability. Power for IC3 is derived from the headlight switch via reverse polarity protection diode D2 and 9V regulator REG2. Regulator REG1 provides a 5V rail to power the rest of the cir­cuit. Recording The recording mode is activated by pressing switch S2 (RECORD). This pulls the REC line (pin 27) of IC2 low, which then pulls the RECLED line (pin 25) low via internal logic circuitry. When this happens, the electret microphone turns on and feeds the incoming audio signal into pin 18 for storage in the EEPROM. At 40  Silicon Chip the same time, LED 1 (RECORD) turns on to indicate that the unit is in the recording mode. Recording either ceases after 16 seconds or when the RECORD button is released, which ever comes first. In either case, pin 25 goes high again and LED 1 and the microphone turn off. Capacitors 3 100µF 16VW electrolytic 1 22µF 25VW electrolytic 2 10µF 16VW electrolytic 1 4.7µF 25VW electrolytic 2 1µF 63VW electrolytic 2 0.22µF 63VW MKT polyester 4 0.1µF 63VW MKT polyester Resistors (0.25W, 1%) 1 1MΩ 2 10Ω 1 470kΩ 4 1kΩ 4 100kΩ 1 4.7kΩ 2 10kΩ Construction Most of the parts for the Talking Headlight Reminder are installed on a PC board coded 01109941. Fig.3 shows the parts layout. Begin the assembly by installing 2-pin and 3-pin headers at the LED and microphone wiring points respectively, then install PC stakes at the switch mounting positions and at all remaining external wiring points. This done, solder in the wire links, followed by the resistors, capacitors, diodes and transistors. Make sure that all polarised parts are correctly oriented and note that the 22µF capacitor near IC1 should be mounted with its body flat against the PC board – see photo. Table 1 lists the resistor colour codes but it’s also a good idea to check them on a digital multimeter as some of the colours can be difficult to decipher. The ISD1416 (IC3) is installed using a 28-pin machined IC socket. This is done because the chip is rea­sonably expensive to replace. The other ICs on pins 4 & 8 of IC1 and pins 24 & 28 of IC2. If these checks prove OK, check that Q1’s collector switches low for about 30 seconds when the PLAY button is pressed. If it doesn’t, check the circuit around IC1 and Q1. Assuming that everything works correctly, the unit can now be installed in your car. There are just three wiring connections to be made: (1) to the negative side of the headlight switch; (2) to chassis; and (3) to the negative side of the ignition switch. In addition, you will have to run two leads to the external speaker. These should be passed through a grommeted hole in the side of the case. Perhaps the easiest way of connecting to the headlight switch circuit is to simply tap into the positive lead to the tail lights. This has two advantages: (1) ease of access (gaining access to the back of the headlights switch is usually quite difficult); and (2) the tail lights come on in both the parking lights and headlights switch positions, so you don’t have to find the parking lights terminal. Note: the unit should warn if either the parking lights or the headlights are left on. Use automotive connectors to interface to the car’s wiring and make sure that all wiring is installed in a professional manner. The last thing you want is a fault in your car’s lighting system due to sloppy wiring. Finally, check that the unit operates correctly in the car and adjust VR1 to give the desired volume level. We recommend that you keep the volume setting low, to minimise any annoyance on those occasions when you do SC trigger the unit. TALKING HEADLIGHT REMINDER MIC + + PLAY REC REC ON + + Fig.5: this full size artwork can be used as a drilling template for the front panel. can then be installed in the normal manner, followed by the two 3-terminal regulators. The two pushbutton switches can now be mounted in position by soldering their leads to the tops of the PC stakes. Use a green switch for S1 (PLAY) and a red switch for S2 (RECORD). Make sure that the two switches are correctly oriented; ie, the flat side of each switch must go to the right – see Fig.2. The microphone and LED 1 are connected to their respective pin headers on the board using light-duty hook-up wire. Take care to ensure that these devices are connected with the correct polarity. Final assembly The PC board is installed on the lid of a small zippy case (130 x 68 x 41mm) and is mounted on 19mm spacers so that the snap action switches just protrude through the front panel. The first step is to attach the front panel and then use this as a drilling template for the four mounting holes. Holes will also have to be drilled for the two pushbutton switches, the microphone and the LED. Note that the larger holes should be made by first drilling small pilot holes and then carefully enlarging them to the correct size using a tapered reamer. Both the LED and the microphone should be a push fit into their respective holes. They can be finally secured in position using a small dab of epoxy adhesive. This done, the board can be mounted in position and secured using machine screws and nuts. Test & installation To test the unit, connect a 12V power supply to the V+ and chassis terminals, then hold down the RECORD button while you speak into the microphone. The message should now replay when you press the PLAY button and should continually repeat for a period of 30 seconds. If it doesn’t work, first check for +5V at the output of REG1 and on pin 6 of IC3. Check also that +5V appears TABLE 1: RESISTOR COLOUR CODES Value 4-Band Code (1%) 5-Band Code (1%) ❏  1 1MΩ brown black green brown brown black black yellow brown ❏  1 470kΩ yellow violet yellow brown yellow violet black orange brown ❏  4 100kΩ brown black yellow brown brown black black orange brown ❏  2 10kΩ brown black orange brown brown black black red brown ❏  1 4.7kΩ yellow violet red brown yellow violet black brown brown ❏  4 1kΩ brown black red brown brown black black brown brown ❏  2 10Ω brown black black brown brown black black gold brown ❏ No. October 1994  41