Beeping Down Counter Circuit

Posted on Feb 4, 2014

The schematic for this project isn`t too, too bad to look at even though it`s not the best drawing/layout for a schematic that I`ve ever done. The basic flow is from left to right. Left side is the state machine, then the 555 timers, then counter circuitry and finally the 7 segment LED output circuitry. The theory section explained this already a

Beeping Down Counter Circuit
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little bit, but the 4 NOR gates will act like a 3 state machine, with the buttons triggering between set and start states and the count down value of 00 moving the system to the `trigger` state. The decade counters are hardwired to load the value of `25` into the system when the set state is activated. The outputs from these counters go directly into the 4511 LED drivers to set the count value on the display. The 556 IC appears as two 555 timers in the circuit. As discussed before one is used as a master or system clock at about 1 Hz and the other is used for generating the 2-5 KHz beep sound. This system is made for common-cathode 7 segment displays, so be sure that`s what you`ve got. Similarly, it would be wiser to add resisters before the A-G inputs, but I got lazy and added a single resistor between the common cathode pin and ground.

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