Using pic chips in a noisy electrical environments

[senojlr]

Does anyone have any tips or suggestions for eliminating noise to the pic chip when used in a noisy electrical environment. I am trying to use a pic 18f252 chip to scale turbine meter pulses in an invironment where there is a lot of electrical noise (motor starters, relays etc.). I have problems with the chip locking up and you have to cycle power to get it going again. I added a .1 bypass capacitor across the power input pins to the pic and it helped a lot but did not completely eliminate the problem. Any suggestions would be greatly appreciated by this Inexperienced newbie.

[mat janssen]

Make your circuit board with big ground copper. Use a 100nF cap. near each supply pin of an Ic. If there is a regulator ic ea LM7805 put near the input and output of this ic a cap of 330nF and an Elco of at least 10 to 100uF.
Make sure that the input wires and supply wires has a multiple windings trough a ringcore.
I hope you can understand what I mean, becouse I am not Englisch.

[senojlr]

Mat would you explain what you mean by big ground copper?

[mat janssen]

I mean, when you look at your circuit board than you see almost everywere copper. ans in between some copper lines which connect the points.
Normally you see only the copper lines from one point to another and the rest is the material of the circuitboard.
Now that part the copper is still there and connected to the 0V or gnd.
If you use dubbelsided printed circuitboards, then do that on both sides.

[sougata]

Hi,

In any pro PCB design software you will find the option of copper pour. It covers the unused areas with copper with the clearence you provide. Normally you can connect the copper pour to the Ground line. For your reference I am attaching two pictures of one of my PCB. One without copper pour and the other with copper pour.

[mat janssen]

Yes, this is what I mean, and if you see still white parts then put the copper there back, and try to connect that to the big parts already there.

[senojlr]

Thanks Mat and Sougata. I understand now. I am just an amateur and I really appreciate you guys taking time to help me. I am going to try this on a prototype board that I am working on. Thanks again for the help.

[Charles Linquis]

I recently had an application where the power was very noisy. The PIC had its own power and ground planes, and hundreds of microfarads of capacitance. Nothing worked until I decided to feed the PIC power plane from the main power through a Schottky diode (very low Vf type). I have 100uF and lots of .1uF caps on the PIC side of the diode.

Now, when the power on the "Main" side drops to a low voltage for a few nanoseconds, the PIC runs on the capacitor "battery". The circuit is now perfectly stable, and even though the PIC now only has 4.53V for VCC, it is still above the minimum of 4.2V.

Charles Linquist

[Acetronics2]

Hi, Charles

I also use that solution for a car electronic ignition PIC supply ... and the power Transistor or IGBT is driven through an opto-coupler !!!

No problem ...

Alain