First function generator (5Hz-20Hz)

This circuit is based on MAX038 IC. Only few other components are required, with good distortion and quality, with variable duty cycle, amplitude and frequency. I think this instrument is absolutely necessary in a electronics lab. Frequency value is set up as follow

Iin / Cf = Output frequency (see MAX038 datasheet)

Current Iin can be set by a current generator or by a Rin resistor with a Vin voltage. Therefore an externalamplifier in closed loop configuration can force the current to a fixed value and so frequency is given by:

Fd = Vin / [Rin x Cf(pFarad)

The maximum frequency allowed, with a fixed Cf will be given by Vref=Vin, configured by a voltage divider (potentiometer). Changing the Cf capacitor differnt range and resolutions are achiveable. For example if Vref was 5V, fixed Cf, the max resistor 57kohm on Iin would set the min frequency allowed and the min resistor 10K would set the max frequency value in the range given by Cf. The following table show some possible range choices:

F = 5V / (Rin x Cf)

Values + e - are dual 12V power supply of all operational amplifiers, when differently specified dual power supply are 5V. Switches S1 and S2 are used to set waveform type: with S1=1 and S2=any value the output will be sin waveform; with both to 0 value the output will be square waveform, if S1=0 and S2=1 triangular waveform will be generated. No high current is required for this circuit, so the powr supply can be very easy to be implemented, using 7812, 7912 e 7805 ICs to provide correct voltages. Switch S3 and 12kohm trimmer can be used to set the duty cycle of signal generated: with S3=1 the duty cycle will be 50%, if S3=0, the value can be choosen with trimmer.