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Build this 90-second message recorder If the 16-Second Message Recorder published in July 1993 wasn’t long enough for you, then try this 90-second model. It runs from a 6V battery & features more power output, a pause but­ton, 90 seconds of continuous recording time & zeropower memory storage. By DARREN YATES There’s no doubt about it – solid state audio recorders are the big noise in electronics at the moment. This was shown by the popularity of our 16-Second Message Recorder project published in the July 1993 issue of SILICON CHIP. So popular was this project that it spawned a couple of pre-built imported surface-mount modules and at least one retail­er is now stocking the device 16  Silicon Chip as a regular catalog item. But as the 286 PC was to the XT, so is this new 90-second sound recorder to that original project. It’s based on the sec­ ond-generation of sound recorder ICs just released by Information Storage Devices. Called the ISD2500-series, there are four mem­ bers each containing 480,000 EPROM cells as opposed to the 128,000 in the ISD1000-series. Despite the popularity of the original design (or perhaps because of it), there were quite a few calls asking “how can you make it longer?” It seems as though people these days leave lots of messages on the fridge! This 90-Second Message Recorder uses the new ISD2590P voice storage IC. It operates from a 6V battery and includes a PAUSE/START key and a separate power amplifier IC. Looking at the IC briefly, instead of using standard digi­tal technology, the ISD2590P uses a patented analog method which allows analog voltages to be stored directly into the EPROM cells. It contains everything to make a complete audio record\playback system from microphone preamplifier to AGC, 480K EPROM storage cells as well as anti-aliasing filters and output amplifier. During recording, this device samples the incoming audio signal and D1 1N4004 0.1 2.2k 0.22 ELECTRET MIC 0.22 S4 +6V 10 10k PARTS LIST 220 16VW 28 7 9 10 16 17 VCCD A6 A8 A9 VCCA 14 10k MIC SP+ 18 MIC REF A OUT 21 6V 10 1k VOLUME 10k LOG 1 3 6 2 4 1k +6V RESET REWIND S2 23 24 100k RECORD R/P AGC EOM 4.7 A0 26 A2 XCLK A3 A7 A5 A4 12 13 8 B A +6V 22k C B E 22k A1 E C VIEWED FROM BELOW 27 6 Q1 BC548 B 25 1 2 8W PLAY S3 PD 0.1 10 20 CE START PAUSE S1 19 470k A IN IC1 ISD2590P 100k 470 5 IC2 LM386 E C LED1 PLAY  LED2 RECORD Q2 BC558  3 4 680  680  5 4.7k K B C E Q3 BC548 90-SECOND MESSAGE RECORDER Fig.1: the circuit is based on IC1, an ISD2590P 90-second voice storage IC. Its output appears at pin 14 & is fed to an LM386 audio amplifier (IC2) which in turn drives a small loudspeaker. Transistors Q1-Q3 drive the PLAY & RECORD indicator LEDs (LED 1 & LED 2). stores these samples as analog voltages in the EEPROM. This technique is eight times more efficient than current digital technology and has the added bonus of zero power for memory retention. In fact, ISD guarantee that it will hold a message for 100 years. And since the writing cycle is much more gentle than the usual digital EPROM programming methods, you can achieve up to 100,000 record cycles with the device. For more details on this device, take a look at the data article published elsewhere in this issue. Operation OK, let’s now go through the operation of the Message Recorder. Initially, when power is applied, nothing will appear to happen. If you now set the PLAY/RECORD switch S3 to RECORD, the unit is ready to record. Pressing the START/PAUSE button S1 once will start the device recording and LED 2 will light up. Recording will continue until either the device runs out of memory or you press either the START/PAUSE button or the REWIND/ RESET button. Pressing the START/PAUSE button will stop recording but will keep the address counter at its present position – it works just like the PAUSE button on your tape deck. Pressing the RESET/ REWIND button will also stop recording but will reset the address counter back to zero. Pressing the START/ PAUSE button again will commence recording from the beginning, erasing any previous recording. To play back what you have just recorded, flick switch S3 into PLAY mode and press the START/PAUSE button. You will now hear the first recording which will continue until either 90 seconds has passed or until the device comes up against an endof-message indicator. At this point, the device goes into an automatic ‘pause’ mode, and by pressing the START/PAUSE button again, you will hear the next recording. At any time, you can PAUSE the 1 PC board, code 01202941, 97 x 85mm 1 battery clip 1 6V battery holder 4 AA size cells 1 red snap-action pushbutton switch 1 green snap-action pushbutton switch 2 SPDT toggle switch 4 10mm tapped 3mm spacers 1 electret microphone insert 1 28-pin machined IC socket 4 PC stakes 1 8Ω 250mW loudspeaker 1 knob Semiconductors 1 ISD2590P 90-second audio recorder (IC1) 1 LM386 low-power audio amplifier (IC2) 2 BC548 NPN transistors (Q1,Q3) 1 BC558 PNP transistor (Q2) 1 5mm green LED (LED1) 1 5mm red LED (LED2) 1 1N4004 rectifier diode (D1) Capacitors 1 470µF 16VW electrolytic 1 220µF 16VW electrolytic 2 10µF 16VW electrolytic 1 4.7µF 25VW electrolytic 1 1µF 50VW electrolytic 2 0.22µF 63VW MKT polyester 2 0.1µF 63VW MKT polyester Resistors (0.25W, 1%) 1 470kΩ 1 2.2kΩ 2 100kΩ 2 1kΩ 2 22kΩ 2 680Ω 2 10kΩ 1 10Ω 1 4.7kΩ Miscellaneous Screws, washers, solder, tinned copper wire. playback by pressing the START/ PAUSE button or reset the device to the begin­ning by pressing the RESET/ REWIND button. Circuit details Let’s take a look then at the circuit diagram in Fig.1. As you can see, there are just two ICs, the ISD2590P and an LM386 audio amplifier IC. The latter February 1994  17 10uF 10k 0.22 22k 22k 1k 0.1 1uF Q1 Q2 680  0.22 470k 220uF MIC IC1 ISD2590P 680  4.7uF 10k 10uF A LED1 A LED2 IC2 386 1 1 4.7k 2.2k Q3 1k 0.1 D1 10  S1 470uF S2 VR1 100k BATT SPKR S3 100k Fig.2 (above): install the parts on the PC board as shown here. Use a socket for IC1 & note that Q2 is a PNP transistor while Q1 & Q3 are both NPN types. Note also that switches S1 & S2 are oriented with their flat edges towards IC1. Fig.3 at right shows the full-size etching pattern for the PC board. IC is used to boost the 2590P’s output signal. Looking at the circuit, the input signal is obtained from an on-board electret microphone insert, which is biased via the 2.2kΩ and 10kΩ resistors. The 10µF capacitor at the junction of these two resistors provides supply decoupling and prevents clock hash from IC1 entering the audio stage. As soon as power is applied, the circuit is switched to a special ‘push-button’ mode by virtue of the fact that address lines A6, A8 and A9 are tied high. The CHIP ENABLE (CE) pin becomes the START/PAUSE control line (pin 23) and the POWER DOWN (PD) pin becomes the RESET/REWIND control. Because these controls are now edge-triggered, only pushbutton switches are required. The AGC (automatic gain control) filter components are the 470kΩ resistor and the 4.7µF capacitor on pin 19. Replay and record selection is made via switch S3. By pulling the R/P input at pin 27 low, the device is placed in record mode and when it is high, it’s in play mode. Switch S3 also controls the two LEDs which display the operating mode. With switch S3 low, transistor Q1 is biased off but Q2 is turned on. With switch S3 high, Q2 is biased off but Q1 is turned on. However, both LEDs are also controlled by transistor Q3, which is driven by the EOM output at pin 25 via a 4.7kΩ resistor. When the START/ PAUSE button is pressed, the EOM line is pulled high for the duration of the first message. This is always the message that begins at address location 0 hex. While the EOM line is high, either LED 1 or LED 2 will light up depend- ing upon the operating mode – LED 1 for PLAY and LED 2 for RECORD. If the START/PAUSE or RESET/REWIND buttons are pressed while the device is either currently recording or playing back, the current operation ceases and the corresponding LED goes out. Since we are using the internal microphone preamplifier, the output which appears at pin 21 must be recoupled back into the main preamplifier stage whose input is at pin 20. This is done via a 1µF capacitor and 1kΩ resistor. Output signal The output at pin 14 is coupled via a 10kΩ resistor and 10µF capacitor to a 10kΩ volume control pot. The 10kΩ series resistor is included to improve RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ No. 1 2 2 2 1 1 2 2 1 18  Silicon Chip Value 470kΩ 100kΩ 22kΩ 10kΩ 4.7kΩ 2.2kΩ 1kΩ 680Ω 10Ω 4-Band Code (1%) 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 blue grey brown brown brown black black brown 5-Band Code (1%) 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 blue grey black black brown brown black black gold brown the loading of IC1’s output stage. The volume control feeds IC2, an LM386 audio amplifier IC. This is connected in its minimum-component mode and has a gain of 20. The output from the LM386 is approximately 300mW into an 8Ω loudspeaker with the 6V supply. Power is provided from a 6V battery, with four AA cells being the most appropriate. Diode D1 provides reverse-polarity protection and the 220µF capacitor provides supply decoupling. Typically, current consumption should be about 6-8mA quiescent and about 30-35mA when recording or replaying. Construction All of the components for the 90-Second Message Recorder, except for the battery and power switch, are installed on a PC board measuring 90 x 97mm and coded 01202941. Before you begin any soldering, check the board thoroughly for any shorts or breaks in the copper tracks. These should be repaired with a small artwork knife or a touch of the soldering iron where appropriate. Next, you should make sure that the components will fit into the holes drilled. You will probably have to do a little work for the mounting of the volume control and the PLAY/RECORD switch. You can use a 3mm drill for the volume control hole and then enlarge it with a tapered reamer or round file to suit. Once you’re happy that everything is correct, start off by installing the wire links. Use the overlay wiring diagram (Fig.2) to make sure that they go into the correct locations, then install the resistors, capacitors, diode and transistors. Note that most of these components are polarised and need to be installed the correct way around for the circuit to work. Again, use the overlay wiring diagram to make sure that everything is correct. Because the ISD2590P is an expensive device to replace, we suggest that you use a 28-pin machined IC socket – not one of the cheaper variety. The cheap ones have a habit of becoming unreli­able after a very short time. Solder the IC socket in the same way you would the IC. You’ll find that the socket has a notch in one end, just as the IC does. This makes it easy to remember which way around the IC must be plugged in if it ever needs to be removed. Next up, solder in the LM386 amplifier IC. Once that has been done, you can install the switches. All of these except for the power switch S4 are installed on the board. The two snap-action switches should fit snugly into position on the board. Make sure that the flat section on these switches if facing towards the top of the board (ie, towards IC1). Testing Finally, insert the ISD2590P into the 28-pin socket. Make sure that it goes in the right way around. This done, connect a 6V battery in series with an external power switch and your multimeter. When the power is switched on, you should find that the current consumption is about 8-10mA. If it’s any more than 15mA, switch off immediately and check the board for possible solder shorts or component positioning errors. If everything appears to be in order, follow the operating routine outlined earlier to record and play back to your SC heart’s content. Subscribe now to the largest faults & remedies library in Australia ✱ ✱ 1994 manuals are now available. Our database is regularly updated with information supplied by technicians such as yourself. ✱ Exclusive backup service by qualified technicians. ✱ ✱ Over 10,000 faults and remedies on file with flow charts and diagrams. Covers Colour TVs and VCRs of all brands sold in Australia EFIL Phone or fax now for your FREE information package ELECTRONIC FAULT INFORMATION Reply Paid 4 P.O. Box 969 AIRLIE BEACH 4802 Ph 079 465690 Fax 079 467038 February 1994  19