Problems using ICL7106 IC and LCD to create an ampmeter display -3 1/2 digits

Thread Starter


Joined Jan 9, 2014

I am using the IC circuit ICL7106 (200mV full scale) and LCD VI-402-DP-FC-S to create an ampmeter display (1 amps max over a 0.1 ohm resistor is 100mV max). I connected the circuit as shown in "typical applications", except I am using +/- 5V power instead of a 9V battery. The +5/-5V comes from a center tapped transfomer(120VAC to 15VAC center tapped). I have checked and verified there is +/-5V coming out, however, there is nothing showing up on the LCD screen. Attached is my schematic. I initially thought the ICL7106 IC was broken and swapped it. Again when I power it on, this time numbers appeared on the LCD screen then they disappeared after ~ 5 mins. When I attempt to power it on again, nothing shows up now. I am confused and appreciate any help I can get to solve my problem, I attached the schematic. :)

upload_2019-1-6_20-55-31.png upload_2019-1-6_20-56-12.png




Joined Jan 29, 2010
hi 619,
When using +/-5V supply they share a Common 0V connection, with a single 9V supply, where is the Ov connection.???
You say:
The +5/-5V comes from a center tapped transfomer(120VAC to 15VAC center tapped)

Do you have a Rectifier/Smoothing and regulation to give +/-5Vdc/???
Post an image showing the transformer secondary connections.
Last edited:


Joined Apr 5, 2008

There is a broken image in your post.
It links to your local disk, wich will not work.
Please upload images to the forum that you want to show.


Thread Starter


Joined Jan 9, 2014
Hi ericgibbs,

The +5/-5 volts have two 10uF caps on the inputs of the LM7805 and LM7905 and two 10uF caps on the outputs of the regulators.

Hi bertus,

Can you see the image now?


Moderators note: uploaded image to forum
Last edited by a moderator:

Thread Starter


Joined Jan 9, 2014
There is a connection from the 1M-Ohm resistor (In High) and a connection from the .02uF cap connected on In low to a voltage that goes up to 200mV max.

Both COMM's of the LCD screen are connected to BP.

Thank you for the help


Joined Nov 20, 2015
It would be useful to know something about the source of the current you are measuring. I do not have experience with this specific component, but it is not a coincidence that the reference design shows the power source as an INDEPENDENT, ISOLATED battery. Likely you are seeing an interaction between the ground references of your +/- 5V supply and the supply current you are attempting to measure. Even though your +/- 5V supply is "isolated" via a transformer, even a small amount of AC leakage (via winding capacitance) or other sneak current paths can make your circuit behave as though it is at a different potential than the circuit you are measuring. If the voltage on a measurement input exceeds the + or - power supply values, the circuit will misbehave or go up in smoke.
I don't have enough info to make an absolute diagnosis, but give it some thought because I suspect this is what's going on.
Have you gone back to the 9V battery temporarily to see if things work properly in that mode?
Good luck!


Joined Oct 2, 2009
Here is a tip on drawing complicated circuit schematics.

Do not feel compelled that you have to connect one pin to another.
Simply label the signal at one IC, for example, E2, and label the corresponding pin at the other IC with the same designator. This will eliminate ugly looking lines with humpbacks on them.

The other way of drawing crossed lines is to draw straight lines. Lines that intersect are shown with a solid dot when they are to be connected.

BTW, you are missing the pin numbers on all your ICs. These are essential. You cannot leave out the pin numbers in your drawings.