To accomplish A/D conversion with V/F converter in a microcontroller system, there are two schemes that can be utilized. First, VIN is measured by counting the FOUT frequency for 1ms, 10ms, 100ms, or 1 second depending on the number of digits of resolution required. The final count is then directly proportional to VIN. (The microcontroller provides the time base) .Second, by determining the time between two pulses (negative edges), Vin is measured. Fout is used as gate for counting the microcontrollers clock. Then, the final count will be inversely proportional to Vin.

AD CONVERSION WITH A MICROCONTROLLER circuit schematic

A value directly proportional to VIN will result by taking the one’s complement (changing 1’s to 0’s and 0’s to 1’s) of the final binary count. When resolution is very important, this technique will give a faster conversation time, but dynamic range is limited. [System’s block diagram source: Microchip Datasheet]