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From a cheap DMM to a custom panel meter: detaching LCD and other hints.

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jchw4:
I recently got an old variac and started looking for a modern volts/amps meter. There are cheap panel meters around but they are very limited. The $20 Zotek (ZOYI, Aneng, etc...) meters are so much better!

So I thought of basically making a panel meter from a cheap DMM.

The first issue seems to be detaching an LCD and making a "display cable".  But I am sure somebody has already tried that.  :) Any hints?

I could not find any zebra adapters, it will probably require a custom PCB. Is it as easy as it sounds?

Did anybody try making a custom LCD zebra strip mount? Are there any tricks that I should better know before trying to design something myself?
(Like should the display PCB match the full size of the LCD or is it enough to cover only the contacts for mechanical rigidity? How much do I need to compress the zebra strip?)

janoc:

--- Quote from: jchw4 on January 15, 2024, 10:25:07 am ---I recently got an old variac and started looking for a modern volts/amps meter. There are cheap panel meters around but they are very limited. The $20 Zotek (ZOYI, Aneng, etc...) meters are so much better!

--- End quote ---

Why would a variac need more than a basic voltage/current meter with a single range?

What are you planning to do with it? Measure capacitors? Probably not, right? Variac is not a multimeter, if you need more accuracy/features for whatever reason once in a blue moon, connect a multimeter to the output!

enut11:
It has been done before. Look at this thread:
https://www.eevblog.com/forum/projects/using-a-fixed-range-ac-voltmeter-with-variable-input/msg2801118/#msg2801118

BTW, digital meters are slow to respond to changes so I also have an analog AC meter to monitor the current. When powering up suspect equipment I start at zero volts and slowly wind up the AC while I monitor the current.

Kleinstein:

--- Quote from: enut11 on January 16, 2024, 05:28:08 am ---BTW, digital meters are slow to respond to changes so I also have an analog AC meter to monitor the current.

--- End quote ---
The speed depends on the AC conerter: the analog RMS converter like AD637 are relative slow, as they need to filter out the ripple quite well to get really RMS at mains frequency.
Some modern meters (both higher grade bench top and rel. low priced handhelds) use digital RMS and can be quite fast with AC, not much slower than with DC. The downside with the handheld DMMs with digital RMS (e.g. UT133) is there limited bandwidth (e.g. 1-5 kHz).

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