voltage controlled waveform generator - an economical AF waveform source

The IC used in this circuit is well known to readers of Elektor. The circuit itself would have been familiar if it had not been for the control circuit around IC2 which replaces the usual potentiometer for frequency control. Readers may suspect that this has something to do with voltage control ... and they would be right. Basically the frequency of this generator depends on the value of capacitor C3 and the current level at pin 7. According to Ohm"s law the cur- rent is dependant on the resistance in the circuit and the voltage across it. The voltage at pin 7 is stabilised at 3 V inside the IC. The current level flowing through R5 (1 k2) will depend on the voltage level at the output of IC2. Obviously, if this is 3 V there will be no current through R5! The maximum level of IC2, the lower the voltage the higher the current and therefore the higher the frequency. The output voltage of IC2 increases with Uin and with a range of 0 ... 3 V the highest frequency is achieved with Uin at 3 V