WAIT FOR THE OPAMP TO START WORKING
The opamp gives the clock signal, the XNOR gives the T flip flop a costant toggle signal. You have to set the desired number to start with, set it with the load in the counter chip, close the SPST switch and wait for the timer to reach zero to start over. I had to use all those logic gates to get a positive signal when the counter reaches zero. The logic gates drive the PNP BJT which cut the way of the clock signal when the timer reaches zero and they automatically re-enable the clock when a new value (≠0) is set. Still have to figure out how to change the opamp timing in order to get an actual timer. Hope you find this enjoyable. If only EC gave more space!!
Now when the timer reaches zero a lamp is lit
