Tiny digital ac volt/amp meter

[camallison]

Just this morning took delivery of one of these http://www.ebay.co.uk/itm/330789414798?s...K:MEWNX:IT&_trksid=p3984.m1439.l2649

Mine was posted in Singapore and arrived after 8 days (far better than HK and China Post deliveries). It is truly tiny (approx 3inch wide and 1.5 inch tall and roughly 1.5 inch behind panel.) but performs well. I am using it in the workshop to give me an idea of any voltage droop (we suffer it here) and heavy current draw by any of my various machines. Useful to keep an eye on this and not burn anything out when we get a brown-out. Apparently the local supply is classified as a farm supply - large housing estate of bungalows built in the 1970s.

Quality of the unit is very high and well made, and only £7 post paid! How on earth do they do it at that price?

Colin

[Yorkie]

Probably too early to ask Colin, but I notice that it says '0 - 50A' and I wondered how far down the current reading will go. In particular, for vintage radio purposes we may want to read just a few mA rather than Amps - I wondered if it went down as low as say 50mA? It mentions that the accuracy of current measurements is within 0.1 Amp, but I don't think we can infer from that what its lowest current reading is.

An amazing little unit and at £7.00 post free, at a rock bottom price! As you say, it makes you wonder just how they do it. Who ever would have thought in the 1970s that pocket calculators would be available for 75p in 2013 - less than the cost of a tabloid newspaper? (75p in 2013 equated to 9p in 1975, at which time calculators typically cost £25.00).

[camallison]

When the wind stops trying to blow the workshop away, I will test it, comparing with a clamp-on I have that is very accurate down to fairly low readings. I doubt though that it will be accurate down to a few mA, but you never know. Looking at their ebay shop, they seem to have many meters on offer and so it might be worth trawling through them. Simple digital voltmeters and ammeters seem to be under £5 post free.

Colin

[Mark Hennessy]

Hi Colin,

I've got a couple of those on the way - glad to hear that they seem OK.

If you get the chance, a picture of the display working would be nice (the listing doesn't show that). I'm being impatient - guessing that my units won't arrive until next week

What resolution are the readings? Are they 3-digit (so, 1V, 0.1A)?

All the best,

Mark

[camallison]

Here it is working on the desk in my study. So, won't display lower than 0.1A.

Colin

[Mark Hennessy]

Thanks for posting that, Colin - much appreciated.

I wonder if it can be taken apart? From what I can see of the pictures, there are two PCBs, it could be that the rear one is power supply and input conditioning - and that might vary from model to model - and perhaps the front PCB is a fairly generic display driver? It might be possible to re-purpose the module. For example, if it could say "DC" rather than "AC", and if it could be re-scaled, then it would be perfect for a bench power supply. Perhaps the decimal points can be moved as well? I'm looking forward to finding out, hopefully mine will arrive early next week

[camallison]

Yes, you are correct in assuming the split of tasks between the two boards. As you would expect, the "splitting" to achieve what you propose is an unsoldering job as the boards are connected using stake pins that are soldered.

It looks as though they use the assembly with different rear boards as the label has multiple options. They are:

AC 100-300v, AC 50A or 100A

AC 75-300V

DC 7-20v

DC 4.5-30v

AC 80-500v

DC 7-30v

and a last "spare" with a space to fill in details.

There are two stake pin connectors, each with four connections and a pair of flying wires labelled + and - that go direct to the display rather than its controller board. The controller board has two tiny trimpots reached through holes in the rear board and these are labelled V-calibration and A-calibration on the ebay listing sketch. The CT is hard-wired onto the PCB, whereas I have seen others that are supplied loose on flying leads.

Tonight, I am mounting mine in a single gang metal back box with the supply to the workshop running through that via terminal blocks in the box. It lends itself to that sort of mounting, being so shallow in depth. The whole power system in the workshop is properly put together with conduit between boxes.

Colin

[camallison]

Probably too early to ask Colin, but I notice that it says '0 - 50A' and I wondered how far down the current reading will go. In particular, for vintage radio purposes we may want to read just a few mA rather than Amps - I wondered if it went down as low as say 50mA? It mentions that the accuracy of current measurements is within 0.1 Amp, but I don't think we can infer from that what its lowest current reading is.

An amazing little unit and at £7.00 post free, at a rock bottom price! As you say, it makes you wonder just how they do it. Who ever would have thought in the 1970s that pocket calculators would be available for 75p in 2013 - less than the cost of a tabloid newspaper? (75p in 2013 equated to 9p in 1975, at which time calculators typically cost £25.00).

In the early 70s, I worked for Commodore in Eaglescliffe as a factory product-introduction engineer on the PET, VIC-20, the small calculators with red numbers with magnifiers in front of each digit, and "Green-line" calculators (http://www.vintage-technology.info/pages...co976m.htm). Contrary to what the site says, the Green Line calculators were made in the UK. We found that product from Japan suffered from poor quality and engineering and so switched production for European and US consumption to the UK. The Japanese had even used a mains shaver lead and socket as the 15v supply lead to the VIC-20!!!!! We only ever took the first batch of 10,000 VIC-20s from them, having to retrofit acceptable leads to all of them before shipment to end-customers.

I still have one each of the two calculators I referred to, and my son has a VIC-20 and PET that I repatriated from the engineering department when we closed down the UK factory.

Colin

[Yorkie]

Thanks for your interesting reminscences Colin - I remember those tiny LED digits with the little magnifying lenses.

I had a Tandy frequency counter that had eight of those digits - quite bright and very clear.

BTW, the website link you quoted can't be reached.

[Joe]

Link fixed.

- Joe