The fun of making ISD1820 voice recording box

This recording box allows readers to experience the fun brought by voice IC. If you are interested, you can also use this production to innovate.

The following table is the component list of this kit.

1. Working principle of the circuit

This circuit uses the 8-20s single-segment voice recording and playback integrated circuit ISDl820P produced by ISD Company of the United States. It uses CMOS technology, and its basic structure includes an oscillator, microphone preamplifier, automatic gain control, anti-aliasing filter, speaker driver, etc. It has high-quality, natural voice restoration technology, and 10,000 voice recording cycles.

Automatic power saving, no power consumption, information is stored for 100 years, the working voltage is 3~5V.

There are four packaging forms for this integrated circuit. In order to facilitate the manufacturer to improve the success rate, the hard package dual in-line 14-pin DIP14 is used, and the character mark is ISD1820P.

The pin functions of the integrated circuit ISDl820P are as follows: Pin 11 is the positive power supply (VCC); Pins 8 and 14 are connected to the negative power supply (VSS); Pin 1 is the recording terminal (REC), which is valid when the high level is high. As long as REC becomes high, the chip starts recording; Pin 2 is edge-triggered playback (PLAYE). When a high level appears on this terminal, the chip starts playing. After starting to play, PLAYE can be released; Pin 13 is the recording indicator terminal (/RECLED). When in the recording state, this terminal is low and can drive the LED; Pins 4 and 5 are connected to the microphone input terminal (MIC); Pin 6 is connected to the automatic gain control (AGC) terminal. AGC dynamically adjusts the pre-gain to compensate for the wide range of microphone input level changes, so that the distortion can be kept to a minimum when recording a large volume change (from whispers to noise); Pins 7 and 9 are connected to the speaker output (SP+, SP-), which can directly drive speakers above 8Ω; Pin 10 is connected to the oscillator resistor (ROSC), and this terminal connects the oscillator resistor to VSS.

The figure below is the circuit schematic. The core of this circuit is the integrated circuit ISD1820PY, and there are not many peripheral components. The key switches S1 and S2 are used for playback and recording control respectively, and the microphone converts the sound signal into an electrical signal.

R3 and R4 are bias resistors for the microphone. The LED serves as a recording indicator.
　　

2. Circuit production process

1. A full set of vital parts

This circuit consists of 4 fixed resistors, 4 ceramic capacitors, 1 electrolytic capacitor, 1 integrated circuit, a microphone, and 1 speaker.　

2. Welding resistors

The resistors in the kit are ordinary resistors with 4 color bands.

3. Welding capacitors

The capacitors in the circuit are divided into ceramic capacitors and electrolytic capacitors. Ceramic capacitors have no polarity: electrolytic capacitors have polarity, the long leg is "10" and the short leg is "1". When inserting, be sure to pay attention to the polarity and use horizontal insertion.

4. Welding micro switch

Before welding the micro switch, measure the switch first, and keep it close to the circuit board when inserting it. Because the switch handle is relatively long, pay attention to apply force evenly when pressing it to prevent damage.

5. Soldering integrated circuits

Integrated circuits have directions. When inserting, match the semicircular groove of the integrated circuit with the semicircle in the symbol to ensure the correct polarity.

6. Soldering LEDs

The long leg of the LED is "+". When inserting it, pay attention to adjust its height to ensure that it fits well with the shell and only protrudes a little from the hole.

7. Welding microphone

Microphones have polarity, and the one connected to the shell is the negative pole. Use the excess wires after welding the resistor to form the legs. When the microphone is inserted into the circuit, it should be close to the circuit board.

8. Connection between speaker, battery and circuit board

Before soldering the speakers and battery cells to the wires, they must be tinned first, then connected to the wires, and then the wires are connected to the circuit board.

3. Circuit installation and debugging

After all the components are installed, place the speaker in the back cover and fix the speaker with hot melt glue or by melting the surrounding plastic. The negative end of the conjoined spring can be properly lengthened to ensure that the battery can be reliably connected. After inserting two No. 5 batteries.

As long as the welding is correct, the circuit will be successful after power on. The debugging is very simple. Press the "record button" and hold it to start recording. The total length is 20 seconds. The recording ends when the switch is turned off. Press the "play button" to play. If it does not work properly, please carefully check the solder joints and components for errors. It will work after correction.