Tyre Guage DRO - capacitance issues?

Thanks everyone, Knowing the problem is 90% of the way to the solution. I will try some of the suggestions, and have ordered a "silver" version of the gauge to see if the plating helps. However now I know what to avoid it does the job.

Mill & lighting is all earthed.

The incident reminded me of one of my favourite quotations from Isaac Asimov

The most exciting phrase to hear in science, the one that heralds new discoveries, is not “Eureka!” (I found it!) but “That’s funny …”

Edited By Peter Cook 6 on 03/04/2021 20:43:19

Hi Peter,

Your earlier comment sounds correct. The lights are generating interference an you are an antenna bringin it close to the DRO. The mill body is acting as a "ground" return capacitively coupled to the DRO. By touching the mill with one hand you and the mill are at the same voltage and the interference has no effect.

I thought it was the other way around with th milll body being the intererence source and you the ground, bu the end effect is the same. The "metallic" cse version my well sort the problem.

Robert G8RPI.

Just an update for anyone interested. I obtained a new "silver" tyre gauge and swapped the front part for the one I was using as the mill DRO.

The problem of the flickering display went away. Presumably the thin coating is sufficient screening to fix the problem. There is a side benefit. Although the devices look identical apart from colour, the new one does not loose its setting when it switches itself off, and comes back on when the quill moves. The old one reset to zero when it switched off, and had to be manually switched on again - so they are different implementations.

In swapping over I had to dismantle the original device and came across another interesting curiosity. The back of the LCD does not appear to have any electrical connection with the PCB.

The display has a strip of what feels like rubber along one edge. I cannot - even with a loupe - see any contacts on the rubber.

While the PCB has a corresponding set of pads onto which the rubber strip presses

I can only presume that the strip of rubber conducts from top to bottom, but not sideways so that matching pads on the LCD connect to the pads on the board. If so that is high tech (and potentially quite useful) material in something that cost me a fiver delivered - so what did it cost to make!!

Edited By Peter Cook 6 on 07/04/2021 17:21:58

Thanks for the interesting and useful update, Peter

... Regarding the rubber : I think you might search for ‘Zebra Strip’

MichaelG.

Thanks Michael - first time I have come across it. Filed for future need! 

Thanks Frances - now I know what it is I can see the construction. Quick waft with a small paintbrush was as far as I went. It worked OK on reassembly

Edited By Peter Cook 6 on 07/04/2021 17:55:33