PIC Microcontroller A2D Input Methods

Avoiding constant current draw in RC A2C converters that use a voltage divider to measure higher than the uP's Vdd.

Oliver Broad [obroad at TELINCO.CO.UK] says:

OK Usual disclaimer, this is an untested circuit but...

Take an N-type logic level FET. Connect the gate to PIC VDD and the source to the measuring pin. Put the capacitor between the pin and ground, the resistor between the drain and the voltage. Drive the input pin high and the FET turns off. No drain at all. Drive the pin low then float it and measure the charge time. Obviously the pin will not rise above the Vdd-FET Vth but this should not be a problem.

PICList Thread '[PIC]: Unknown Voltage on PIC pin.'

Questions:

• RANDA_JO_7@HOTMAIL.COM asks: " WHAT ARE THE SUITABLE TYPES OF ADC TO CONNECTED WITH PIC16F877A" James Newton replies: Just about any type of ADC can be connected to an '877 or the ADC that comes in the '877 can be used. See the DATASHEET for the '977 at microchip.com for more information.