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# LED Panel Meter

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#### GuinnessGuy74

##### New Member
Hey Guys,

I am new to this forum and I have to say that reading through some of the posts, it is quite helpful. I have a pair of digital 3-1/2 digit LED panel meters that I found and I would like to hook them up as a voltmeter and ammeter. I looked online and they look to be a pair of CX-102A's. They have 10 pins. I know how meter movements work but never dealt with digital LED displays before. I am used to full-scale deflections using current but it seems to me that these work off deflection voltage (200mV) to achieve 1999. So do I just have to set up a voltage divider so as at max voltage the deflection is 200mV? Also with 200mV being the culprit, could other scales be achieved, like say instead of output scales of 2, 20, 200 could I get outputs of 3 and 30? or does the meter not permit that?

Jim
Long Island, NY

Think about it, 3 1/2 digit means that the first digit (MSD) can only be a "1".
Not possible to have a "2" or "3" as the first digit with these.

Maximum digit (3 1/2) display will always be 1999.

Thanks

Thanks, I didn't know exactly what that 1/2 digit was. So I guess there is no way to make this 30.00 volts, but if I adjust the decimal place to the right once can I get 30.0 etc. or .999mA?? If I can, then am I right to use a voltage divider network to lower 30V(fullscale) to 200mV? Albiet the resistor values will be funky but is this possible? Thanks for the help guys!

Jim

Jim, if you ignore the first digit you can get the other 3 digits to display any number from 0 to 9
The meters maximum direct input voltage is 1.999V. For bigger voltages you need a voltage divider. If accuracy is not paramount you could use a fixed 1% resistor and a 20 turn cermet trim pot to get around the tricky resistor values.
For current measurements you need a shunt resistor, this obviously has to be able to handle the current without getting too hot at full range. Due to the low value of the shunt resistor you should include a fuse as well.

I have a leaflet here that came with a OEM 3 1/2 digit liquid crystal display module. The range settings are quite straigt forward, should be similar with yours. Just make sure you do not connect the power supply to your module in reverse, some of them do not like that :wink:

Oops, meant to say that the maximum direct input voltage is 1.999mV, more likely - sorry.

Many Thanks

Klaus,

Thanks for the help. You made it a little more clear to me now. I really appreciate the help!! i am sure I will need more in the future..lol

Jim

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