0
\$\begingroup\$

My lab uses a custom-built setup to generate reactive plasma; basically metal plates in a vacuum desiccator energized by a BD-10A. I've built an arduino-based control box for it to allow more precise operation than plugging it in and out of the wall socket allows. The box works well, except that when the plasma is generated, the LCD(GWT-C1627A-RGB) gets scrambled and displays arbitrary characters instead of the output from the arduino. I assume the 500 kHz signal from the plasma is getting picked up by the wires connecting the arduino to the LCD. The LCD digital input seems to have a clock speed of 2 MHz. I was going to try to shield the input wires, but I don't know if that's likely to work, or how to go about it if so. Any advice would be appreciated!

Edit: Here's a slightly outdated image of the wiring inside. It's a bit more controlled now, but the ribbon cables stretching to the top in this image are still what connects to the LCD. Image of control box internal wiring

\$\endgroup\$
2
  • \$\begingroup\$ what does the system look like? what parts of the control box are connected to the plasma machine? do they share the same power supply or same electrical outlet? \$\endgroup\$
    – Miron
    Apr 26 at 21:44
  • \$\begingroup\$ I've included an image of the wiring. The control box is powered by usb, connected to a separate outlet than the BD-10A. The box controls the plasma through a powerswitch tail 2 ( adafruit.com/product/268 ). Activating the BD-10A in atmospheric pressure doesn't scramble the display, that only happens when plasma is formed. \$\endgroup\$
    – timeskull
    Apr 26 at 22:12

2 Answers 2

1
\$\begingroup\$

These situations are tricky as it can be hard to determine where the noise is getting in.

Some suggestions:

  1. If the LCD module has a metal frame then connect that to 0V(gnd).
  2. put the electronics in a metallic enclosure. Keep the power switch tail external.
  3. shorten the wiring to the LCD.
  4. move the powerswitch tail further away.

The suspicion is the noise is coming in via the powerswitch tail and finding its way back via USB. The metal frame of the LCD works as an antenna and couples energy into the circuitry.

A more scientific method would be to get a spectrum analyser and near field probe to get a idea of the freq of the noise and where it is coming from. Armed with this information you can better target the problem.

\$\endgroup\$
0
\$\begingroup\$

Have you considered STP cable for everything? Choice of ground = 0V is critical and power supplies can pick up radiated noise also to create interference.

So you can require everything then carefully choose your 0V ground common point to reduce the ingress or radiated plasma noise at 500 kHz to 10 GHz.

I might be inclined to use microwave TV coax for critical signals.

RF caps and ferrite beads can also do magic.

You got some redesign to do.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.