Voltmeter's LED display

[kulakovs]

Hi guys. I found THIS schematic for my diy voltmeter. The problem is i can't find a LED display like in the schematic. I have got 2 choices of displays that could fit:
1)There's a 4 digit, 7 segment LED display, but it only has got 12pins (the one in the schematic 2x7 has got 18pins). Is it possible to connect that display to ICL7107?
2)And the other one is a 2 digit (I'd need two of those) display with 18 pins, but It's a common cathode display (the one in the schematic is common anode). How do I connect that common cathode display correctly? As I understand I'd need to connect nr.14. and 13. pins to -5V (not +5), and that's it?

 

[cr0sh]

Couldn't you use 4 common anode 7-seg individual displays instead?

 

[DemonicSandwich]

The first, four segment, display is multiplexed. Each didget has it's Anodes connected together.
Then the A segment from all the digits are connected to one pin, then the B segments and so on so you can't use it with this.

There are a wide veriety of 7-seg displays available.
For example, four of these would work but since these are single digit they have a different pinout that the double digit ones in the diagram.

While two of these will work in the diagram pin for pin.

 

[kulakovs]

if 1st choise falls back, then i will have to use two 2x7 18pin common cathode displays, since there is no common anode display in my local shop. how do i connect it properlly?

 

[audioguru]

The ICL7107 IC is designed to drive a common-anode display, not common-cathode.
If you use a common-cathode display then each segment and DP will need to be driven by a logic inverter (32 inverters are needed).

An LED display uses a very high power supply current. The IC gets hot which affects its accuracy. Use a low power LCD display instead with an ICL7106 IC. Or buy an inexpensive LCD voltmeter module.

 

[bountyhunter]

I see cheap 3 1/2 digit voltmeters at harbor Freight Tools for as low as $3. Seriously. Ain't worth building your own digital display.

 

[audioguru]

If you need to see an inexpensive LCD voltmeter in the dark then use a flashlight (cold torch).

 

[shilpagupta]

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