How Does the 555 Synth Work?

The circuit is split into two functioning units. The first unit is an

astable oscillator consisting of the potentiometers RV2 to RV13



, switches S1 to S12, resistor R1, capacitor C3, and 555 timer IC2. When no switches are pressed, the astable circuit cannot function as there is no connection between the charging/discharging resistors and the timing capacitor C3. When a switch is pressed, current flows from R1, through the various potentiometers and then into C3. This results in the 555 producing an oscillation that forms the base audio frequency of the synthesizer.





The second unit is a monostable formed by components RV1, C2, and the second 555 timer (IC1). When the trigger input is pulsed the 555s output goes high for a period of time depending on the resistance of RV1 and the capacitance of C2. The larger the value of either (or both) the longer the time the 555 output remains. The trigger for the monostable is connected to the output of the first oscillator which creates a continuously triggered monostable signal (and hence a tone).

When the length of a monostable pulse becomes longer than the duration between two trigger pulses, the output frequency of the monostable suddenly drops (as the monostable is triggered only once every two input triggers). If the potentiometer is varied so that the monostable length is shorter than the width of n pulses, then the frequency suddenly increases. Hence, the function of the Atari Punk Console is realized.