The purpose of this circuit is to create different sound effects with the press of a button. It is powered (hopefully) by four D cell batteries.
The ISD1790 referred to in the circuit is a multi-message voice record & playback chip manufactured by Winbond, the datasheet can be found here:
http://www.datasheetcatalog.org/datasheets2/36/368701_1.pdf
When the circuit is first powered up only the ISD1790, U1 (a 4017 counter) and a 7555 pulse generator for the U1 clock signal are “hot”.
U1 cycles through it’s outputs at a 7Hz rate (as dictated by the pulse generator) waiting for one of the momentary pushbutton switches (at each of it’s outputs) to be pressed.
When a switch is pressed, it triggers another 7555 timer (U4) to send a high signal to the ENABLE Pin of U1 stopping U1’s cycling and holding the pin of U1 associated with the particular pushbutton pressed high until U4 times out (approx 3 secs).
The reason for this is to essentially lock-out all the other pushbuttons until the initially pressed button has performed it’s function (ISD1790 has played it’s associated sound and the timer has timed out. – I set it up this way because little fingers are not going to wait to push other buttons.
Once the button has been pressed, U4 goes high and powers up a second 4017 counter whose clock input is controlled by the ISD1790’s RDY pin. RDY is normally HI but goes LO during a FORWARD or PLAY pulse to it’s respected inputs.
The first step is to send a LO pulse to the ISD1790’s RESET pin which causes this chip to reset to it’s initial state (all counters reset to zero).
Then a HI pulse is sent to the 4017 (U2) clock and a LO pulse to ISD1790’s FORWARD pin causing it to skip to the next recorded sound. Once LO goes to FORWARD it causes RDY to send a LO to U2’s clock signal causing U2 to switch to the next output- this progression will continue until U2’s output matches the HI output of U1 (through the 74HC08 AND gate).
Once U2 matches U1’s HI output, a HI signal is sent to U2’s ENABLE pin through the AND gate. This cause U2 to stop cycling, a LO pulse is sent to ISD1790’s PLAY pin causing it to play the associated sound.
See how the HI to 1790’s PLAY pin also causes the U4 (7555) to time out yet still holds U1 (4017) ENABLE pin HI until it has finished playing it’s sound effect.
Any suggestions / critiques are welcome. Thank you!!
