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Read a recent post on VCO using PSoC3 and thought it might be fun to directly port the traditional Astable MV circuit into a PSoC architecture.
A traditional Astable multivibrator using OpAmp would have looked like this
This is a dual supply circuit. The Opamp used as a comparator has its output charging a capacitor through a resistor, the RC constant of the setup responsible for the frequency. The resistive divider is used to switch threshold on either side of the ground thus providing a different threshold voltage for each of the output state of the circuit.
The same functionality can be mimicked in the PSoC by having a polarity controlled IDAC and capacitor to act as the RC circuit. Now the switching threshold can be easily achieved by using the hardware anaog mux in the GPIOs.
The advantage here is that the IDAC value directly determines the frequency of the output. The circuit can be modified to have a switching IDAC data bus in the two phases thus providing duty cycle control too.