Personal Message Recorder Circuit
Posted on Sep 13, 2012 5227
The persona] message recorder is built around an ISD1016 CMOS voicc messaging system, which does away with the cumbersome and expensive analog-to-digital and digital-to-analog conversion circuits. A functional block diagram of the ISD1016 is shown. The ISD1016 contains all of the functions necessary for a complete message-storage system. The preamplifier stage accepts audio signals directly from an external microphone and routes the signals to the OUT (analog out) terminal. An automatic-gain control (AGC) dynamically adjusts the preamplifier gain to extend the input signal range. Together, the preamp and AGC circuits provide a maximum gain of 24 dB. The internal clock samples the signal and, under the control of the address-decoding logic, writes the sampling to the analog-storage array.
Eight external input lines allow the ISD1016`s message space to be addressed in 160 equal segments, each with a 100-millisecond duration. When all address lines are held low, the storage array can hold a single, continuous, 16-second message. However, there is a special addition to the POWER DOWN input (pin 24) of Ul. If the internal memory becomes full during recording, an overflow condition is generated in order to trigger the next device. Once an overflow occurs, pin 24 must be taken high and then low again before a new playback of record operation can be started. Transistor Ql, C3, R5, and R6 form a one-shot pulse generator that automatically clears any overflow condition each time that start switch (SI) is pressed. Switch S2 selects cither the playback or the record mode. Switch S4an 8-position (a-h) DIP switchis included in the circuit to allow the circuit`s record/playback time to be varied from 0 to 16 seconds. The maximum time available is when all 8 switch positions are closed (or set to the on position)..Resistor network R8 (a-h) is included in the circuit to provide a pull-up function for the address lines, which thereby controls Ul`s record/playback time.