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

Thread Starter

Big_Earl619

Joined Jan 9, 2014
9
Hello,

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

 

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ericgibbs

Joined Jan 29, 2010
12,253
hi 619,
When using +/-5V supply they share a Common 0V connection, with a single 9V supply, where is the Ov connection.???
E
Update:
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:

bertus

Joined Apr 5, 2008
21,253
Hello,

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.

Bertus
 

Thread Starter

Big_Earl619

Joined Jan 9, 2014
9
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?

big_earl_display.jpg

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

Thread Starter

Big_Earl619

Joined Jan 9, 2014
9
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
 

rphare

Joined Nov 20, 2015
9
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!
 

MrChips

Joined Oct 2, 2009
23,080
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.
 
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