noiSe, maybe you should look at either opto-isolate the comm lines or use a
RS485 that uses differential voltages to read the signal.

michael

-----Original Message-----
From: Mr Teik Siong <tsk196@SOTON.AC.UK>
To: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
Date: Monday, March 23, 1998 1:48 PM
Subject: Grounding problems


>Hello Engineers;
>        I have a project that controls the position of the
>motor. And I have managed to use PIC17C44 to control it
>successfully.
>        However, I had to erase the PIC whenever I wanted
>to change the parameter of the PID. So I decided to make it
>user friendly by having the computer to communicate with
>the PIC.
>        And I did manage to get the computer to communicate
>with the USART of the PIC.
>        But when the RS232 had the same ground as the
>motor, the motor starts to go unstable. When I remove the
>RS232 from the circuit, the motor is stable again.
>        Does anyone of you knows what is happening?
>        Thanks in advance to all engineers.
>With regards,
>Siong.
>
>----------------------
>Mr Teik Siong
>tsk196@soton.ac.uk
>