DIY LED Display Voltmeter

[mrbaseballny]

I've been searching the internet for some solutions to my problem and came up with the stuff below. I wanted to add a integrated LED display voltmeter to my Foam cutting supply box, so that I could have a visual reference to how many volts was going to my bow for cutting foam. I am using a 25.2 VAC 2-amp Transformer, with a pot to adjust the current going to my bow. I found this LED display voltmeter schematic, but its DC not AC. I looked up the ICL 7107 IC on mouser.com and got the specs. Now I"m not a electronics guru, but I think that I can replace the analog IC with one that will handle AC instead of DC?? Am I interpreting this right?? Can anyone help straighten me out, maybe give me a small electronics lesson?? I know its quite complex, but anything would help out:)

I guess it would help if I gave you the complete url so you can check it out yourself if interested http://www.electronics-lab.com/projects/test/014/

Here's a part list:
Parts List


R1 = 180k P1 = 20k trimmer multi turn
R2 = 22k U1 = ICL 7107
R3 = 12k LD1,2,3,4 = MAN 6960 common anode led displays
R4 = 1M
R5 = 470k
R6 = 560 Ohm

C1 = 100pF
C2, C6, C7 = 100nF
C3 = 47nF
C4 = 10nF
C5 = 220nF


Thanks in advance:)

Mrbaseballny

[jeffs555]

You just need an AC to DC converter on the input. The intersil data sheet for the ICL7107 has a schematic of one in figure 21. http://www.intersil.com/data/fn/fn3082.pdf

[mrbaseballny]

Won't that AC to DC convertor defeat the purpose of the power supply? What I mean is if I convert AC to DC then won't the output of the power supply now be DC instead of AC?? I was thinking of placing the LED voltmeter in between one of the outputs to the hot wire to measure the volts. I think I'm all confused now:(

Thanks for the help though:)

mrbaseballny

[Reuben/HotRod]

You still use the AC output of the supply for your hot wire, but the converter just goes between the supply main output and the display circuit you have...

[oldphart]

Surely I if you put the ac/dc converter across the hot wire ,and feed the meter from it ,the meter will see the DC while the cutter sees a AC.I would do a circuit diag ,but they never come when I try

[mrbaseballny]

OK, I understand now. I can use a separate power source for the + and - 5v to power the meter right?? or could I power it off the power supply and just use a power regulator??

[Dan Baldwin]

All electronics has an LCD panel meter for $7.00, but it would have to be powered from a separate 9-12 volt power supply, and you would still have to convert the AC voltage to DC for measurement, and it would need to be scaled to 0-200 mv.

http://www.allelectronics.com/cgi-bin/category.cgi?category=385&item=PM-200&type=store

Dan

[Mr.RC-CAM]

Why not use a low cost DVM? The can be found for under $10 if you look hard enough. And when you are aren't using the bow, the meter can be used for other things too. Or, build it into your system for a custom look.

For example:

http://www.allelectronics.com/cgi-bin/category.cgi?category=760&item=DVM-810&type=store

http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=33499

http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&category%5Fname=CTLG%5F011%5F008%5F002%5F000&product%5Fid=22%2D810

RC-CAM

[mrbaseballny]

Why not use a low cost DVM? The can be found for under $10 if you look hard enough. And when you are aren't using the bow, the meter can be used for other things too. Or, build it into your system for a custom look.

For example:

http://www.allelectronics.com/cgi-bin/category.cgi?category=760&item=DVM-810&type=store

http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=33499

http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&category%5Fname=CTLG%5F011%5F008%5F002%5F000&product%5Fid=22%2D810

RC-CAM
My main reason for not stripping down a inexpensive DVM is I am limited for space, the case I have everything in now, is nicely seated, and the digital LEDs would fit nicely without much problem. I also wanted somewhat of a challenge as I'm new to electronics.

[Dan Baldwin]

I just got a flyer from Harbor Freight. They have a digital multimeter for $2.99.

http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=30756

Dan

[Mr.RC-CAM]

The link is broken. Here is the one they have on sale at the web site: http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=90899

I soldered a resistive load in mine and use it to check airborne packs at the field.

RC-CAM

[crvogt]

I have a few of the Harbor Freight meters and they are really quite good, cheap enough at $2.99 to add one to the flight kit, have a pair set up on the bench one for current and one for voltage... May stop and get a couple more to tear them apart and mount in another box, one set preset for 0-20v, the other 0-10A. Will post some pictures as the project progresses.. I was thinking of adding one of the displays from one of the HF meters built into my battery charger.

Carl

[Marion]

I have several of the Harbor Freight meters. They seem to be pretty good. They check very well against a precision voltage reference. You sure can't beat their price!!

[mrbaseballny]

O.K. I just got my board completed for the LED display voltmeter, and I built the ac/dc convertor, I'm going to hook them up on my breadboard to make sure they work together. Man, this will be one "sexy" looking power supply, in a nice neat small footprint enclosure!! And it beats having to disassemble one of those Harbour frieght DVM. Those just weren't what I needed for my design layout. Pictures to come soon:)

Mrbaseballny

[simingx]

If possible, try to power the DVM module off a seperate supply, as (if memory serves) the ICL7107 et al doesn't like high "common mode" inputs (i.e. it can't measure sources which share a common ground with it's own power supply) without some extra circuitry...

For info, see "Overcoming Common Mode Range Issues When Using Intersil Integrating Converters" , http://www.intersil.com/data/an/an9609.pdf