crazylefty:
I'm looking to make a few, to measure voltage of various PC components and display them all using different 4x 8 segment displays
They would only need to have a small range, like say a 3V meter would only need to read from 2.5 - 4V, and 12V from 11 to 13V.
Not quite sure what you are needing, but I have been buying modules from eBay for a few dollars each - red, yellow, green, blue 3 digit displays, two variants, one with two wires and one with three wires. Since the specified power source is 3 to 30V, the two wire ones are limited to that range and are best for monitoring supply rails, while the three wire ones have the same supply range but indicate 0 to 100V.
Would measuring the field made passing the current from the voltage through a coil with a linear Hall sensor be any good? The more loops, the more sensitive.
Nick,
SparkFun has a multimeter that uses a m168.
While the s/w is not arduino it wouldn't be that difficult to convert to an Arduino
sketch if you wanted to.
For your use, one of the more interesting things might be the interface circuitry they used.
Here is a link to their site with links to all their documentation:
Now since I know you are alot like me and like to do fun and goofy stuff
all in the name of learning stuff....
Here is the really fun part of a project like this.
Enhance it to talk.
Yep, it isn't that tough.
If you weren't aware, Here is a link to a VERY COOL Arduino library that can give you the speech capability:
Might also be fun to upgrade your capacitance meter to talk as well.
The speech tables have all the needed words like
volts, milli, micro, farad, etc...
bperrybap:
Nick,
SparkFun has a multimeter that uses a m168.
While the s/w is not arduino it wouldn't be that difficult to convert to an Arduino
sketch if you wanted to.
I've got that. It works OK, but of course there are limitations in input voltage ranges, polarity, etc.
30V full scale, 5mV smallest unit? 500mA, 1mA smallest unit? 10k and 100k ohm resistance ranges? 11.2k ohm input impedance for voltage, one ohm current sense resistance?
A toy. There is no challenge to build a meter with those very modest specs. My first meter was a Micronta (Radio Shack) kit analog meter, it had much better specs than that one.
Back when FET input Op Amps first came out and the only 10Mohm input meters were VTVM (Vacuum Tube Volt Meter) and FETVOMs, I built my own 10Mohm input (well, actually 11.111Mohm) analog voltmeter. I found, with a little thought, that rather than use a 9M, 900k, 90k, 9k, etc. resistors to make a scale that went by 10s, use 10M, 1M, 100k, 10k, 1k, and 111 ohms. That resuls in a scale that goes by 10s to within a fraction of a percent. The resistor tolerance swamps any error caused by using 111 ohms rather than 111.11111.... ohms.
Protection is the hardest part. In my case, every meter then was manually switched and it was up to the operator. However, I never had the Op Amp input connected directly to the input, it was at the lowest scale still at 1/10th the input and was reading 500mV on that scale. I had a couple of antiparallel diodes to ground.
Sorry to bring this thread back from the dead, but has anyone accomplished this?
After a very stupid move on my part, I trashed a few parts trying to make an ACS712 work: I trashed an Atmega328, MAX603, MAX604, MAX412, ACS712.
I gave up on having a proper reading on the ACS712, and I am beginning to wonder if the MAX133/134 is a good solution, since it is the IC used in many DMM and can be interfaced with a microcontroller. It is a pretty expensive IC, 'though.