Regarding about ICL7107 7-segments display.

Hi all,

I'm current doing one multimeter using icl7107 following the steps as below:
https://www.circuitstoday.com/digital-voltmeter-using-icl7107

Here is the one I did on schematic using dipfree:


But the problem is, I can't calibration the 7segments as it always showing -1666/16.66 by moving the potentionmeter at the ICL7107's pin 36.

Is the clock running?, because it should show 000. Looks as though there is a big DC bias somewhere but I can't read your schematic.
Frank

chuckey said:

Is the clock running?, because it should show 000. Looks as though there is a big DC bias somewhere but I can't read your schematic.
Frank

Click to expand...

I think it's not running because it never show 000. By the way, where is DC bias?

The schematic looks wrong. Where does the current through the display flow? It should also have decoupling capacitors across the incoming and regulated supplies. I assume the incoming regulator U2 is a 7805 and U3 is a 7660.

Brian.

betwixt said:

The schematic looks wrong. Where does the current through the display flow? It should also have decoupling capacitors across the incoming and regulated supplies. I assume the incoming regulator U2 is a 7805 and U3 is a 7660.

Brian.

Click to expand...

Sorry. That was mistake. The input of the display will be on Pin 3 and connected to the output of U2 which is the 7805.
Yes, U2 is 7805 and U3 is 7660.
So, if I follow the capacitor's value and resistor's value, it should be working right?

Yoiur diagram is drawn confusingly but I think it's correct. Try using the TEST pin to check the display driver is working as decribed in the data sheet. If it is, using a DVM check the voltage across the IN_HI and IN_LO pins to confrm there isn't actually a voltage there.

Brian.

betwixt said:

Yoiur diagram is drawn confusingly but I think it's correct. Try using the TEST pin to check the display driver is working as decribed in the data sheet. If it is, using a DVM check the voltage across the IN_HI and IN_LO pins to confrm there isn't actually a voltage there.

Brian.

Click to expand...

I used Pin 37 at the 7107 at I obtained -1888 value from display. This means that the circuit is correct right?
I short circuited the In_HI and IN_LOW and obtained 000 but then, when I used to measure a 1.5V AA battery from that two inputs, it does not show any value on the display.
The display will randomly show numbers.

Good, the display is working properly and by shorting the input it suggests the measurement is also working. The next thing to check is the resistor values you used. You don't show any values on the schematic but I suspect you have copied them from the 200mV FSD schematic in the data sheet. This means the maximum voltage you can measure is 0.199V so applying 1.5V would take it well over range.

The other thing to watch is the power supply, the display will take quite a lot of current so as the segments turn on and off the drain on the power supply will change. If you do not fit decoupling capacitors across the regulator input and between the V+ and V- to ground you almost certainly will have instability on the supply rails and this will result in random digits. I suggest you fit a 10uf and 100nF capacitor in parallel across each of those points to keep it stable.
See if that fixes the problem.

Brian.

betwixt said:

Good, the display is working properly and by shorting the input it suggests the measurement is also working. The next thing to check is the resistor values you used. You don't show any values on the schematic but I suspect you have copied them from the 200mV FSD schematic in the data sheet. This means the maximum voltage you can measure is 0.199V so applying 1.5V would take it well over range.

The other thing to watch is the power supply, the display will take quite a lot of current so as the segments turn on and off the drain on the power supply will change. If you do not fit decoupling capacitors across the regulator input and between the V+ and V- to ground you almost certainly will have instability on the supply rails and this will result in random digits. I suggest you fit a 10uf and 100nF capacitor in parallel across each of those points to keep it stable.
See if that fixes the problem.

Brian.

Click to expand...

Oh, but I do not have that capacitor value. How about both 100nF?
But there stated can for 20V range just by modifying R4 in the https://www.circuitstoday.com/digital-voltmeter-using-icl7107.
(R4=1.2K gives 0-20V range, R4=12K gives 0-200V range ).
By the way, the Dot of the display which is Pin 5 I modify to 3rd segment, is it ok for that?

100nF is better than nothing at all but really, the one at the input pin of U2 should be 100nF and a larger value in parallel to ensure stability, particularly if your power supply wires are longer than a few cm.

It's important to understand that the 7107 does not 'auto range', to measure higher voltages you use a resistor divider outside the IC and connect the appropriate dot in the display yourself. For example, if you divide the input by 10 you move the decimal dot one place to the right to compensate. The IC does not do this for you so if you have different measurement ranges, as you change divider you also change the dot that's connected in the display.

Your schematic shows the unit measuring the voltage at the junction of R8 and R9, so it should give a reading as soon as you switch it on. Without knowing the resistor values I can't predict what the display should show but it may be working properly already.

Brian.

Man, it turned back into -1666.
https://i212.photobucket.com/albums/cc37/lonelyhouse/2013-04-03013217.jpg

I try to adjust using the trimpot to calibrate but nothing changed.
All values same with the **broken link removed**

It's difficult to see from the photograph but I can only see two wires going to the 7660 circuit. Do you have the ground connected to it?

If you have another voltmeter can you measure the +V and -V pins relative to ground and tell me the readings you see.

Brian.

betwixt said:

It's difficult to see from the photograph but I can only see two wires going to the 7660 circuit. Do you have the ground connected to it?

If you have another voltmeter can you measure the +V and -V pins relative to ground and tell me the readings you see.

Brian.

Click to expand...

It been fixed by just removing the the IC7805 due to the not enough power to power up the icl7107.
Thanks for helping.