Problem with grounding in PIC16F877

[u04f061]

Hi,

I am having problem with PIC16F877. First, I have simulated my program in Proteus and it works fine, so there is little chance of a programming problem. But in hardware, my controller works well if I touch it with hand(when I am connected to earth). Morover, I have tried the following:

1 - As I am using PORTC(PORTB and PORTD) of the PIC, I have tried both pulling it up and down, through a variety of resistors, but it did not give the right output.

2 - I have checked and re-checked the floating ground problem, but in vain. I have also tried different power supplies, but did not succeed.

3 - When I do not touch it, the PIC does not turn off, rather it gives a wrong output. This wrong output is a clock at some pins and any pulse with a different cycle on the others.

4 - I have directly and indirectly shorted the pin to earth, but of no use. Moreover, I connected a resistor equal to my body resistance and tried to pull the pin and up through it, but still it did not work.

At last, I want to clarify that it actually does work when I earth it through me. I have checked for a variety of outputs.

 

[the_edge]

Re: Problem with PIC?

Did you put capacitor for filtering supply? If you didnt, put 10µF capacitor just on the exit of voltage regulator...

I often had some stupid problems with my pic if I didnt put it... If this is not it, than I dont know))

 

[rkodaira]

Re: Problem with PIC?

General tips:

1) Don´t forget to connect both Vdd (2 pins) and Vss (pins) in the 16F877.

2) Don´t forget to connect bypass/decoupling 100nF capcitors near (the nearest the better) the Vdd to Vss pins.

3) Breadboard circuits can introduce parasitic capacitances in the oscillator/crystal circuits.

4) Put the crystal near the osc pins of the PIC.
Shorter connections and tracks are recommended in this aspect.