How to wire a LCD panel meter to amplifier?

[Thomasdj]

Hi!

I just bought a LCD panel meter to install in my amp to measure cathode voltage..but how to hook it up?? I know this is properly an odd question but I have no experience in these things.. :|

It has 13 pins:

1 = V+
2 = V-
3 = NC
4 = NC
5 = COM
6 = INLO
7 = INHI
8 = RFL
9 = RFH
10 = ROH
11 = D1
12 = D2
13 = D3

It’s a common ground, 0 - 200mv meter.

What to connect to what?

Thanks

Thomas

 

[mister_rf]

cx101bg schematic

It will be more simple if you mention the part number of the LCD multimeter

Not for sure only guessing

1 = V+ positive voltage- power supply connection to the meter.
2 = V- negative voltage- power supply connection to the meter.
3 = NC not connected
4 = NC not connected
5 = COM –common=ground
6 = INLO input low Negative measuring input.
7 = INHI input high Positive measuring input.

8 = RFL reference low maybe Connect to COM= 0V ground
9 = RFH reference high
10 = ROH reference out Precision reference voltage output. Connect to RFH for normal operation.

For the decimal point there are two possibilities, first one
11 = D1 connection for dot 1 maybe Connect to 0V to display DP1 (199.9).
12 = D2 connection for dot 2 maybe Connect to 0V to display DP2 (19.99)
13 = D3 connection for dot 3 maybe Connect to 0V to display DP3 (1.999)


second one

11 = D1 connection for dot 1 maybe Connect to V+ to display DP1 (199.9).
12 = D2 connection for dot 2 maybe Connect to V+ to display DP2 (19.99)
13 = D3 connection for dot 3 maybe Connect to V+ to display DP3 (1.999)

 

[Thomasdj]

Re: Panel meter wiring

Thanks for your reply!

It still not work:|

The meter is called CX101BG

here is a link to the datasheet

https://www.circuitspecialists.com/images/CX101A&B&BG.pdf

Thanks,

Thomas

 

[mister_rf]

Re: Panel meter wiring

So in the datasheet You have all the details needed.
A final variant for the pinouts
1= V+ positive voltage- power supply connection to the meter in this case a +5V
2= V- negative voltage- power supply connection to the meter in this case GND from 5V supply
3 = NC not connected
4 = NC not connected
5 = COM –common=ground
6 = INLO input low Negative measuring input.
7 = INHI input high Positive measuring input.
8 = RFL reference low maybe Connect to COM= 0V ground
9 = RFH reference high
10 = ROH reference out Precision reference voltage output. Connect to RFH for normal operation.

For the decimal point there are three possibilities each one related to the scale needed for the voltage measured in the circuit.

11 = D1 connection for dot 1 maybe Connect to V+ to display DP1 (199.9).
12 = D2 connection for dot 2 maybe Connect to V+ to display DP2 (19.99)
13 = D3 connection for dot 3 maybe Connect to V+ to display DP3 (1.999)

I have attached a schematics how to use the display.
Because the multimeter is set to measure a maximum 200mV at the input, we need to arrange a voltage divider to meet our needs. This is done using two resistors: R1 and R2.
You didn’t specify what’s the maximum voltage in the circuit to be monitorized.
For a resistor divider it’s important only the ratio R1/R2, the range of resistors it’s selected only for minimize the current drawn from the tested circuit.
And because of the tolerance values of the resistors we need to have at least one resistor adjustable to obtain a proper calibration of the circuit. It’s more simple to adjust the R2 and in practice we replace R2 by two other resistors: a fixed one plus a variable one.

Vin=Vsource R2/(R1+R2)

You need to provide maximum voltage for the Vsource, we choose R1=10MΩ, Vin =0.2V
To be determined R2
Example
Vsource 20V
R2=R1/99=101.01KΩ we split R2=R2’ + R2’’= 82kΩ (fixed)+ 25kΩ(variable)

Example
Vsource 200V
R2=R1/999= 10.01KΩ possible solution R2=R2’ + R2’’= 8.2kΩ +2.5kΩ

 

[Thomasdj]

Re: Panel meter wiring

Thanks for your help

I have attached a schematic of my setup.

I want to measure the cathode voltage from each power tube in a tube amp..I want a built in panel meter which I can turn on/off when I want to adjust the bias.

I only need to measure between 0-200mv, which is why i thought this meter would be perfect to the job

I've got a 7805 to generate the +5v

Should I connect COM, INLO and RFL together (negative measure point) ?
INHI (Positive measure poin)

RFH together with RFH

Do I need any external resistors? (except from the 1 ohm cathode resistors from the valves)

Best regards

Thomas

 

[mister_rf]

Re: Panel meter wiring

In theory you don't need any resistors, but in practice you will put one for safety reasons, a 100K and also 4 1N4148 diodes to limit accidentally high voltages applied to inputs.

Yes COM, INLO, RFL connected together

and RFH connected to ROH

 

[mister_rf]

Re: Panel meter wiring

And one suggestion for connecting cathodes. In my opinion in order to avoid some glitches in the system I will prefer to have connected permanently the 1 ohm resistor to the cathode and it will be shortcircuited in a normal use. For testing purposes the ground wire will be disconnected and have introduced the resistor in the circuit.

 

[Thomasdj]

Re: Panel meter wiring

Thanks!

I'll try this setup tonight and install the 1 ohm res permanently!

Best regards

Thomas