Sound note on the ISD1416 chip (ISD1420). Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Application of microcircuits

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Wanting to leave a message to absent family members or colleagues, many use notes left in a visible (or agreed) place, or special boards. You can simplify and speed up this procedure if you use a device based on the ISD1416 (ISD1420) chip [1-3] as a storage medium - just press the record button and say a message. It is just as easy to get information - just click on the appropriate button. These microcircuits are devices for recording/reproducing audio information and are based on the technology of storing an analog signal in multilevel non-volatile memory cells. It should be noted that this technology does not require the use of analog-to-digital and digital-to-analog conversion, and the information is stored in analog form.

The ISD1416 and ISD1420 ICs include an AGC microphone amplifier, a sample-and-hold device, fifth-order active low-pass filters, an AF amplifier with a direct-drive head connection output, a clock generator, and a 128K memory device. The sampling frequency of the first microcircuit is 8 kHz (the upper limit of the reproducible frequency band is 3,3 kHz), the second one is 6,4 kHz (2,6 kHz), the recording / playback duration is 16 and 20 s, respectively. The information storage period guaranteed by the manufacturer is up to 100 years, and the number of recording cycles is up to 100000.

A schematic diagram of an audio note is shown in fig. 1. Turning on the microcircuit is typical, two buttons are used to control the operating modes: SB1 (Record) and SB2 (Playback). When you press the first of them, the microcircuit is activated, a polarizing voltage is applied to the BM1 electret microphone and the HL1 LED lights up, signaling that the recording mode is on. Recording takes place as long as the button is pressed. After the above time limit has elapsed, the microcircuit automatically switches to standby mode. Since it draws less than 0,5µA (typical) current in this mode, there is no dedicated power switch.

Rice. 1. Schematic diagram of an audio note

To listen to the entire phonogram, it is enough to briefly press the SB2 button. At the end of playback, the microcircuit switches back to standby mode. If desired, the device can be "attached", for example, to the front door, in this case, playback will automatically turn on when it is opened. To do this, the device must be supplemented with an XS2 socket and an R9C6 interference suppression circuit, and a miniature switch (sensor) should be installed on the door, which will connect (through resistor R9) pin 24 of the DA1 chip to a common wire. An autonomous power source can be a battery of three galvanic cells or four AA nickel-cadmium batteries. To recharge the latter from a power supply with a voltage of 12 V, the elements VD1, HL2, R8 and the XS1 socket must be inserted into the device. The HL2 LED is a charging indicator; when an external power supply is connected, it will glow. Zener diode VD1 limits the voltage on the battery. The value of the resistor R8 is selected based on the required charging current of the battery.

As HL1, you can use any LED with a working current of 5 ... 10 mA, the allowable forward current of the HL2 LED must be at least that necessary to charge the battery. The BM1 microphone is an electret SZN-15E, MKE-332 or similar, when connecting it, the polarity must be observed (the "+" terminal is connected to the resistor R1). Dynamic head - any small-sized with a resistance of 16 ... 50 Ohm, polar capacitors - K50-6, K50-12, K50-35 or similar imported ones, the rest - K10-17. Resistors - MLT, S2-33, P1-4, buttons - any small-sized without fixing in the pressed position. It is convenient to use a magnetically controlled contact (reed switch) as a door sensor by installing it on the door frame, and attach the magnet to the door. It is permissible to use the RES55 relay (more precisely, its contacts), there is no need to disassemble the relay itself.

Most of the parts are mounted on a printed circuit board made in accordance with fig. 2. It is placed in a housing made of insulating material of suitable dimensions, on the walls of which sockets, buttons and a dynamic head are fixed. The device does not require adjustment.

Rice. 2. PCB

If desired, the HL1 LED can be excluded. In this case, a jumper wire is installed instead and R7 is replaced with a 10 kΩ resistor. Reducing the dimensions can be achieved by using resistors and capacitors for surface mounting, small-sized disk batteries (for example, D-0,125) and a dynamic head from headphones with the above resistance. When placing the board at a large (several meters) distance from the sensor, it is advisable to use a shielded wire to connect them and, in addition, you may have to increase the capacitance of the capacitor C6 and the resistance of the resistor R9 several times.

Sources of

1. Podorozhny S. Chip-Corder microcircuits for recording and reproducing speech. - Radio, 2001, No. 10, p.20.
2. Description of microcircuits of the ISD1400 series. - winbond-usa.com/products/isd_products/chipcorder/datasheets
3. Partin A. Sound module on a single chip. - Radio, 2002, No. 11, p.40.

Author: I. Nechaev, Kursk; Publication: cxem.net

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