ADC Load

Just wondering if there is a way to minimize the loading down of the I/O. I have a 22uF capacitor attached to the AN0 pin on a F452 and it works great until I remove the signal. The capacitor will hope and release the charge over a great period of time which is not what I want. If I put in a load resistor to discharge the capacitor is drops my voltage being measured on the I/O by about 1V at 3V, I'm using a 10k but this is having a major affect in the readings. I can probably adjust the scale to compensate for the increased load if I have too. Is there something that I'm missing?

Must use a buffer made with an operational amplifier. TTL inputs are low impedance this is why the voltage across capacitor drop fast.

regards

Ok i admit it, i can't really understand what you want to do. When i read you message it sounds like you want the capacitor to be discharged as quickly as possible. If this is what you want, you could make the pin low output, wait a short time and then switch it back to an input. This will release the charge in a controlled manner. If, on the other hand, you want the capacitor to keep the charge longer you should make an OPampbuffer as suggested.

/Ingvar

Actually I'm just using the cap to help smooth the input which seems to be working really good and stable. I have now looked at all the numbers being read and compared them and have determined that vin = vin / 2 + vin + 2. This seems to work very good.