Hello Fellows,

I need a digital voltmeter that will display the voltage for this voltage regulator I'm building. I want it to be very accurate but couldn't find anything. I want it to be either a LCD display or an LED display. I came across this:

http://www.electronics-lab.com/projects/test/014/index.html

Although, the IC seems to be obsolete. Does anyone know of an IC that will provide the same function?

Appreciate the help!

 

What is the range and what accuracy do you require?

 

Digikey has more than 2000 ICL7107 ICs in stock today for less than $5.00US each.
Maybe your food store doesn't sell them.

The project at Electronics-Lab is still full of errors. Make the circuit shown in the datasheet instead.

 

Google "digital panel meters" if you don't want to have to build one from scratch.
See Circuit Specialists Inc. as an example. Note that some meters require an independent power source (ground is not common with signal being measured). Others allow a common ground.

 

Check Marlin P. Jones and Associates (mpja.com). It has compete digital panel meters for less than $10 each. You will need to decide whether you want a separate supply for the meter or to power the meter from the supply it is measuring. If it is the latter, there are selections that do that right out of the box, but you can also accomplish it usually by creating a negative voltage (e.g., ICL7660).

If it is the former, and you plan to use batteries, be sure to consider current drain. LED meters are probably out of the question. Another option is to hack an inexpensive meter from a place like Harbor Freight. Some of its meters are about $4, maybe less on sale.

What range of voltages do you need to measure?

John

 

Thanks for the replies everyone,

I am building a LM338 adjustable regulator that goes from 1.2V-30V. So I am building a power supply and wanted to vary my voltage and read the display. I don't think I want to use the ICL7107 because it's an older part, I'm sure they have far accurate ones. As for accuracy, I want to get as accurate as I can.

 

MPJA has several meters that might fit that range. Their selection is listed here:

http://www.mpja.com/products.asp?dept=52

The model 16177 ($9) has several ranges that include 0-199.0 V. I have used the 16565 ($10) and show how to modify it to give a range of 0 -199.9 Volts here.

Both meters can share a common ground with your supply.

John

 

MPJA has several meters that might fit that range. Their selection is listed here:

http://www.mpja.com/products.asp?dept=52

The model 16177 ($9) has several ranges that include 0-199.0 V. I have used the 16565 ($10) and show how to modify it to give a range of 0 -199.9 Volts here.

Both meters can share a common ground with your supply.

John

So I guess I'll have two wires that I connect to the output of my voltage regulator? I am going to have a transformer and rectify it for DC (from AC outlet) to power the regulator, but I guess I could also have another tap that will supply 5V to the voltmeter.

 

Yes, the panel displays will require a fixed voltage, usually 5V, to operate.

Don't forget the other, simple option of hacking an inexpensive, battery powered voltmeter.

John

 

Yes, the panel displays will require a fixed voltage, usually 5V, to operate.

Don't forget the other, simple option of hacking an inexpensive, battery powered voltmeter.

John

Yeah, ok. I might as well get a transformer with two taps. Sounds good!

 

You'll need 4.5 digit resolution to get a display that reads to 1/100V for a 30V supply. They're more expensive, but are available off-the-shelf. Here's one source:

http://www.rpelectronics.com/English/Content/Items/PM-328.asp

By the way, you'll be interested to learn that you can make your design adjust down to zero by biasing the adjust pot to -1.25V instead of ground. Please see attached (incomplete) schematic jpeg.

I'd also suggest using a 10 turn pot to allow more precise adjustment due to the wide range you're seeking.

 

Yeah, ok. I might as well get a transformer with two taps. Sounds good!

This unit draws a whopping 1mA. I suspect most LCD units have similarly low power requirements. If you get the 5V version with common ground, you won't need another transformer winding. You can power it from the same unregulated DC the powers your supply. You would need something like a 78L05, and maybe a zener to drop its input voltage to a safe level.

 

Ok guys, I found this LCD display in my junkbox. I'm thinking it might actually be a voltmeter! There are two pictures, on the back it says "94V-0" and it says "SGD GX1602A5" Does anyone know where I can get the information for this? I think it is made by these guys: http://www.goldentek.com.tw/english/index.htm but they don't seem to have a search bar where I can enter the number.

 

I could not find that exact part number on the Goldentek site, but part number GC1602A* is there. That is a character display module with a 16-pin input. No picture is given, but the size seems about right. The pin out is shown on page 8 here: http://www.goldentek.com.tw/english/pdf/Dongguan/GC1602A0/GC1602A0SAN2B .pdf

If that is correct, it is simply a display module, not a volt meter. Save it.

John

 

Could I make a circuit to make it a voltmeter? If so, what circuit could I use?

 

Austin,

My advice would be to complete your power supply based on the advice you have gotten here. Save the LCD display for another project later, perhaps when you want to do something with ADC and micrcontrollers.

John

 

Austin,

My advice would be to complete your power supply based on the advice you have gotten here. Save the LCD display for another project later, perhaps when you want to do something with ADC and micrcontrollers.

John

Ok, thanks John.

 

I stumbled on this tutorial for using an LCD display without an MCU. Once you get your power supply built, you may want to play with it (see page 5; confirm connections with the link given yesterday).

http://www.datsi.fi.upm.es/docencia/Micro_C/lcd/HowtouseLCD1.pdf

Just change LCD1 to LCD2 for part 2, which does use an MCU.

John

 

I stumbled on this tutorial for using an LCD display without an MCU. Once you get your power supply built, you may want to play with it (see page 5; confirm connections with the link given yesterday).

http://www.datsi.fi.upm.es/docencia/Micro_C/lcd/HowtouseLCD1.pdf

Just change LCD1 to LCD2 for part 2, which does use an MCU.

John

Interesting, this looks like it would be good for a future project! Thanks again John!