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Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061
Hi all. Between #hvcomm, posts on here and helpful pointers, its clear that I need to get my act together and build a proper multimeter with built-in auto calibration.
Can anyone suggest features to add? So far I have:-
Standard V/I/R via clamp meter, and remote probe with temperature sensor built in, Use HD44780 display in low current mode for long battery life, Capacitative pickups for high accuracy, and low loading, High voltage up to 250000V (no typo) via remote stick meter a la "EPE", Fully documented and open source, Recharge via USB, solar and wireless energy, Built-in datalogger and "black box" to see what fried it Built-in logic analyser and USB or Bluetooth remote sync to desktop, Laser power meter to 2W with wavelength compensation, Head-up display (HUD) using semisilvered mirrors+mini projector.
Registered Member #3324
Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276
ok, this seems rather ambitious, i would sepearate everything out into sepeate devices and have a centeral module that reads them connected by fibreoptics
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061
Not really, a lot of hassle can be avoided by using a customised sensor for each mode. This also means one unit can measure lots of different parameters with a sequencer, avoiding lots of meters connected and the associated rats nest.
Say you wanted to measure a battery charging. The meter could measure:- voltage, current into battery, impedance (via AC methods), and even auto beep when a given parameter exceeds its rating. Ideal for test jigs and other custom applications.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Well, you can get a very good multimeter for a couple of hundred pounds. And you'll need one to calibrate your home-made meter anyway. So if you just wanted a good meter, it would be much easier to earn the money fixing broken IPhones and laptops, and buy one.
If you want to build one as a project, I'd suggest concentrating on the odd features that you can't buy. 250kV range, heads up display, laser power measurement and so on.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
It's often necessary to monitor three different values at the same time - for example only, anode current, screen grid current, and control grid current - to set circuits up properly, so I'd advise people to get three editions of the same inexpensive meter, rather than a meter of the all singing all dancing variety.
I tested the volts range of a £10 ebay multimeter against a Fluke 887AB differential voltmeter, and found only a few percent difference on any range - immaterial to all but a very few real world applications.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061
Which one was it? I've got a few "cheap" meters but the best one seems tio be a cheap unbranded one with black case and orange knob, with transistor test range. So far it has only fried twice, both times were easy to repair. As far as I can tell the accuracy on all but the lowest current range agrees with my other meter so it *should* be fine.
Only thing it really needs is an insulation test as this is a real pain. Something like a 1000V at 0.1uA CW generator inside the meter, controlled by a button sequence. Shouldn't be too hard, just use a voltage divider to convert the 1000V down to sensible levels and then display directly in megohms.
Registered Member #3888
Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649
Don't forget inductance measuring. That's something I really wish I had a meter for. found this circuit that converts a voltage meter into an L meter. Need to order the chip though, my salvaged ones don't seem to work.
The HUD idea sounds cool, but it would require a whole lot of extra work that doesn't seem very necessary. I'd work on that last probably.
I imagine you plan to use a microcontroller to do all the fancy analyzing right?
An auto ranging function for some of the measurements could be cool too. By that I mean you could press a single button to measure resistance and it would cycle through the various ranges until it found the best one and then display it. If you then weren't satisfied with what it picked, you could use the up/down buttons (which you'd probably have anyways for menu options or w/e) to manually cycle the ranges. I imagine the same idea could be applied to capacitance, frequency, inductance, and voltage with a bit of careful planning (you'd want to start at the highest range and work your way down for voltage.) Then based off of what setting and range it was on, could display an xxx.xx number along with proper prefixed units (u,m, , k, M)
You could also have a 16 pin IC socket on the face of it where you could plug in one of your favorite IC's, select the type from a menu option, and then it would test it to see if it was working. This might be very difficult though because you'd need a programmable circuit arrangement for each type. Perhaps just a high/low impedence test could be run across certain pins and then compared to a set of known values for that chip (wouldn't test complete function of the chip, but could tell if it was fried)
A magnetic field sensor might be useful too if you want to find the operating or saturation level of a magnetic component.
lol. To enable the high voltage testing you could have a breathalyzer sensor on it to discourage (or encourage if you program it the opposite way) the drunken operation of dangerous equipment. Ok now I'm getting into pointless stuff. Let's see if you like any of my other ideas before I go on.
I've had mine for a couple of years and found it reliable. The yellow rubbery case has an open out leg like a picture frame, so you can set it up at 45° on the bench, and view the large LCD display from a distance while you work. Great value.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061
Yeah, inductance measurement is handy which is why I have a Peak Atlas LCR for that. Plus they are very helpful at Peak and charge a sensible amount for calibration. Not like some companies like the one which offered to "calibrate" my IDM65 for £48 ... + shipping!
Forty wrote ...
Don't forget inductance measuring. That's something I really wish I had a meter for. found this circuit that converts a voltage meter into an L meter. Need to order the chip though, my salvaged ones don't seem to work.
lol. To enable the high voltage testing you could have a breathalyzer sensor on it to discourage (or encourage if you program it the opposite way) the drunken operation of dangerous equipment. Ok now I'm getting into pointless stuff. Let's see if you like any of my other ideas before I go on.
Dude.. you owe me a new keyboard !!!!!! Coffee everywhere. Actually this IS a good idea, but who is going to be drinking while coiling?! thats got to be a Darwin Award for sure. I have a breath alcohol sensor here from one of those "Christmas Cracker" testers, very sensitive and trips 1 foot away from my open acetone container. Needs 3V at 130mA for the heating element but it does seem to work.
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Build your own custom multimeter
