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LCD voltmeter for my power supply

obito

Apr 13, 2023
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Hi, buddies. I'm building some power supply and I need test the LCD voltimetter what I bought for this project but I don't have its features/specs. Well the seller said "you can measure from 0v to 100v DC" but I'm not sure about that, further, I don't know right values for feed this device.
So, my CUESTION IS... Where I can find the datasheet? The device have the code LF-107-004-V5 but I didn't get info.
 

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danadak

Feb 19, 2021
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Post a pic of backside connector and any labels on PCB next to connector
pin.


Regards, Dana.
 

bertus

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Nov 8, 2019
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Hello,

Is there no info on the page where you bought the meter?
It looks like a red led meter and not an LCD.
On a LCD you would not see the digits when not powered.

Bertus
 

kellys_eye

Jun 25, 2010
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Those meters typically display the measured voltage AND take their power from the same source on the same pair of wires.

Whilst they do work they WON'T work if the supply voltage drops below a minimum level (not sure what that is but 8-10V seems to come to mind)
 

obito

Apr 13, 2023
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Post a pic of backside connector and any labels on PCB next to connector
pin.


Regards, Dana.
Of course, I took this photo:
 

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obito

Apr 13, 2023
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Hello,

Is there no info on the page where you bought the meter?
It looks like a red led meter and not an LCD.
On a LCD you would not see the digits when not powered.

Bertus
Well, Sorry. You're right. It's just 7-segment display
 

Harald Kapp

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These typically come from China and are all more or less the same. On this page there is a wiring diagram included.
 

obito

Apr 13, 2023
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And just what was it that started your concerns...??
Mmm... Maybe i was thinking that for the price. Just like 3 dollars for this voltage range...

These typically come from China and are all more or less the same. On this page there is a wiring diagram included.
Hello,

Here is the wiring @Harald Kapp talked about:
View attachment 58738

Bertus
Hey, thanks. Can be very useful looking aliexpress-alibaba for electronics devices. Well, if you said are same all devices from China that means what I can apply 20v without without fear of spoiling it.
 

Kiwi

Jan 28, 2013
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Suggest that you put reverse biased diodes across both the red and yellow wires to the black wire.
Inductive spikes will kill these cheap meters.
 

danadak

Feb 19, 2021
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The protective diodes Kiwi recommended on yellow line should look
like this (lower left) and for red (upper right) :

1681639847044.png

You can omit the 100K to ground for yellow circuit if you are
concerned about the small error it creates as a V divider on
the yellow input. Leaving it in - Vyellow = (.99 X Vin).

The zener in upper right should be min 9.6V if 9V alkaline battery.

Regards, Dana.
 
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