Voltage to Frequency Converter

Although dimming the brightness of the LEDs could have been accomplished by using a 555 IC timer, I had a few spare KA331 Voltage to Frequency converter ICs from an earlier project that could accomplish the same task quite nicely. This chip was found to be ideally suited the role of providing the means necessary to modulate the intensity of the LEDs because one of the application examples provided by its data sheet was that of a light intensity to frequency converter.

As can be seen from the schematic above, the clock will contain a calibrating potentiometer on board so that most CdS photocells of varying resistances can be utilized without any need to change the circuit. The 10M ohm resistor in parallel with the sensor is in place to prevent the resistance becoming too high and thus causing the frequency, being generated by the KA331, from decreasing to a low enough value to be noticeable to the eye.