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Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I think taut band suspension is the simplest.
I fully agree with the other comments in this thread though. Making a meter might look very simple, but the devil is in the details. It is a difficult precision engineering job to make an accurate one. Ash, do feel free to try it and write us a project thread, it would be very interesting.
Multimeters are cheaper than panel meters just because there's a large market for them. Anyone who does DIY, car electrics, and so on, will want a basic multimeter for his toolbox. I have seen people buy a half dozen of the cheap digital ones and zip-tie them to a board to make an instrument panel.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Steve McConner wrote ...
I think taut band suspension is the simplest.
I fully agree with the other comments in this thread though. Making a meter might look very simple, but the devil is in the details. It is a difficult precision engineering job to make an accurate one. Ash, do feel free to try it and write us a project thread, it would be very interesting.
It looks like I'll have to knock something up now, just to prove a point
Your idea of 'taught band suspension' sounds pretty simple, but may suffer from rubber degradation over time (depending on materials used.)
Once I locate my stock of supermagnets (samples from the factory just off the M1 at Barlborough Links, near Chesterfield) I'll knock up a test-rig.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
The band is usually made of metal, not rubber. It isn't my idea, it is an industry standard design invented by Crompton or some such company.
The simplest meter movement is the cheap and nasty moving-magnet one found in car battery chargers, that would be a good starting inspiration for a DIY design. Then you can work up to making replacement 50uA FSD movements for Avo Model 8s.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Steve McConner wrote ...
The simplest meter movement is the cheap and nasty moving-magnet one found in car battery chargers, that would be a good starting inspiration for a DIY design.
That's what I had in mind when I suggested it to Magnet18.
I'm sure I could build replacements for AVO's, but I couldn't afford the advertising campaign necessary to capitalise on it.
I also don't have anything accurate enough to calibrate it against.
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
Uzzors wrote ... Here's your opportunity: I'd rather spend my time scaling a bunch of micro-ammeters to whatever ranges I needed rather than make fifteen from scratch.
Yes, what Uzzors said. It's silly to make analog meters from scratch (except as an exercise). But not hard to computer-print and attach your own scale cards (e.g. 0-110 volts AC, 0-5 amps DC). The meters are all the same inside, except for series or parallel resistors (and in the AC case, diodes) which you can add by yourself.
p.s. I'm another happy customer of "kwtubes" on ebay.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Klugesmith wrote ...
Uzzors wrote ... Here's your opportunity: I'd rather spend my time scaling a bunch of micro-ammeters to whatever ranges I needed rather than make fifteen from scratch.
Yes, what Uzzors said. It's silly to make analog meters from scratch (except as an exercise). But not hard to computer-print and attach your own scale cards (e.g. 0-110 volts AC, 0-5 amps DC). The meters are all the same inside, except for series or parallel resistors (and in the AC case, diodes) which you can add by yourself.
p.s. I'm another happy customer of "kwtubes" on ebay.
I agree
But if you have no money you have no choice.
Total cost of these is ~$35 and they will still need resistors to calibrate to the required ranges, and to achieve accuracy greater than 10%.
They are still 250 uA FSD, but I'd agree this is the way to go.
I did consider suggesting trying to obtain meters from old cassette players, but thought this might not be very productive, plus they are quite small.
BTW I'm planning to get some neodymium magnets from Maplin next week. ~£1.50 each, so I can 'knock up' some larger, more accurate meters, just to prove a point.
I would advise Magnet18 that if he has $35 he should buy the ones Uzzor's reccommended, though......and obtain plenty of resistors.....
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
Ash Small wrote ... ... But if you have no money you have no choice. ... Total cost of these is ~$35 and they will still need resistors to calibrate to the required ranges, and to achieve accuracy greater than 10%. ...
It's worthwhile noting that "Magic Eye" tubes, used as signal strength meters in pre-transistor radios and tape recorders, were cheaper than mechanical meters.
(image credit: Ake Holm)
If you already have the infrastructure to produce vacuum tubes, and the equipment already has appropriate filament and anode voltages, then a magic eye is just a few bits of welded wire and sheet metal in a glass bulb. Inherently well matched to the signal voltages and impedances, with no magnets, bearings, springs, coils, pointers, lamps, ...
[edit] and I guess mechanical meters had plenty of cost-reductions not yet invented.
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Where to procure meters?
