Hi.

I'm working on a project with PIC18f97j94 microcontroller. My project design includes 3 PCBs, 1 main PCB for the general machine(which works fine), and 2 PCBs according to the need for a bigger machine. Here is the problem I'm connecting 2 PCBs to the main one via flat flexi wire. Each additional PCB has 2 input sockets for buttons. When I apply voltage to those sockets buzzer rings except for one pin ( port-F bit-2 ). When I do shortcircuit test it shows no sign of a problem voltage is reaching to pin but it doesn't ring the buzzer. if remove the flexi wire and apply it directly to the pin then it rings. Also, I thought maybe some components are badly produced so used an empty PCB for it still has no change. Does anyone have an idea what might be the cause of the problem?

 

Welcome to AAC.

I am having a little trouble being sure I understand the problem. Is this correct:

The flexible ribbon cable normally includes the signals to sound the buzzer but one particular input doesn't work, If you remove the cable and apply the signal to the pads on the PCB instead it does work.

Have I got it right?

Also, is the pin being pulled high or low?

 

Welcome to AAC.

I am having a little trouble being sure I understand the problem. Is this correct:

The flexible ribbon cable normally includes the signals to sound the buzzer but one particular input doesn't work, If you remove the cable and apply the signal to the pads on the PCB instead it does work.

Have I got it right?

Also, is the pin being pulled high or low?

Hello.
First, thank you for your reply. And yes you get it right. in the normal state, it's gnd and I'm applying 3.3V to pin. Also, I want to underline that there is no bad connection as I can see because it passes shortcircuit test. and when I apply 3v3 to the socket I can measure it on the particular pin.

 

Purely speculative, unfortunately, but it seems that although you are measuring 3V3 on that pin, I assume that is unloaded? If there is a problem on the other side of the cable that is loading the output intended to pull the pin high, the additional load of the MCU input could be enough that it can't provide the required current.

I wonder what would happen if you were to put a pull up resistor on that pin that didn't bring the pin high but reduced the current needed from the ribbon cable.

Also, how are you pulling it low for the off state?

One other random idea is to see if making the pin active low instead with a pull up to keep it high would work where active high doesn't.

It is mysterious, at least with as much information as I have, Do you have a schematic of the relevant circuits?

 

Purely speculative, unfortunately, but it seems that although you are measuring 3V3 on that pin, I assume that is unloaded? If there is a problem on the other side of the cable that is loading the output intended to pull the pin high, the additional load of the MCU input could be enough that it can't provide the required current.

I wonder what would happen if you were to put a pull up resistor on that pin that didn't bring the pin high but reduced the current needed from the ribbon cable.

Also, how are you pulling it low for the off state?

One other random idea is to see if making the pin active low instead with a pull up to keep it high would work where active high doesn't.

It is mysterious, at least with as much information as I have, Do you have a schematic of the relevant circuits?

I think I got the problem. The problemed one seems to be the compiler. When I manually closed all registers (supposed to be default closed ) that include the mentioned pin before register initialization, then It works well. As I understand when I connect the wire contreller goes crazy.
I hate unreasenable errors...
Thank you for your time sir. I appereciate alot.

 

I am glad you found the problem. Please come back and contribute if you have the time and inclination. I am sure there are people you could help.