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Old 10th Nov 2022, 1:55 pm   #1
dave_n_t
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Default (another!) ESR meter

I rather liked the look of the following circuit

http://zpostbox.ru/simple_esr_meter_circuit.html

for a number of reasons:
- low current consumption at 1.5V, meaning I could use something small like an 'N' cell (which used to come in the Poundland £1 battery mix, and for which I have no other uses)

- it used a 1mA meter. I have one with a broken glass, for which a plastic replacement would be OK for this use (not requiring vast accuracy)

- common-or-garden components

I used a 2.2mH wire-ended miniature choke, which seems to work ok; and BC549C transistors (because I have lots of them). I changed the bias 'sensitivity' resistor chain (originally 51k plus 1M in series) for 100k variable plus 820k resistor plus 500k preset. This allows zero-setting a little more easily.

I scanned the scale, edited out the markings, and truncated it at 0.8mA, before printing out and sticking to the reverse of the scale (so the original, marked 1944, is still there!) The 0.8mA marking became the new 'zero ohms' with a little headway to make the zero-setting even easier. I used standard 5% carbon resistors to do the calibration (although really, this is more of a go/no-go instrument).

The housing was a home-made corrugated cardboard box, with a few coats of varnish to stiffen it; and judicious use of PVA glue, and a hot glue gun.

I'm pretty happy with the result. The only small issue is that it takes a while to settle down: I guess 1mA through either transistor has a small warming effect, so the zero setting is readjusted a few times until it settles.

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Old 21st Nov 2022, 12:31 am   #2
linescan87
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Default Re: (another!) ESR meter

Hi Dave,

I came across this design a few years ago and was going to make it but I acquired another ESR meter. This thread spurred me on and I knocked one together today. I used 2N3904s. Quite happy with the results.
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Old 21st Nov 2022, 9:48 am   #3
PaulDarzi
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Default Re: (another!) ESR meter

Hello Dave,

As you say a nice simple yet elegant design (nice touch having the LTspice model, too), am pondering a go myself but have a lot on currently - so not yet anyway.

However, your box approach has me fascinated would never have thought of doing that in a million years, may I ask, how well does such a box fair in practice?
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Old 21st Nov 2022, 12:22 pm   #4
Nickthedentist
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Default Re: (another!) ESR meter

Quote:
Originally Posted by dave_n_t View Post
The housing was a home-made corrugated cardboard box, with a few coats of varnish to stiffen it; and judicious use of PVA glue, and a hot glue gun.
Love your zero-cost enclosure and re-use of a war surplus meter with hand-drawn scale
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Old 21st Nov 2022, 1:05 pm   #5
Bazz4CQJ
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Default Re: (another!) ESR meter

Nice project Dave. I don't have an ESR meter, I'll add it to the list...but the list moves slowly.

I'm a big fan of cardboard box construction; picked it up from a kid who was a few years older than me in the school radio club back in the 60's, and brought it back in to action when the simple and cheap ali boxes went off the market. On the bench on front of me is a variable power supply unit based on a 4Ah SLA which is built in a cardboard box. I use it to power mini-drills when working outside (on the cr). And Glue Guns, I value my £3 gun most highly. Gluing tool and poor mans' 3D printer .

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Old 21st Nov 2022, 5:16 pm   #6
dave_n_t
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Default Re: (another!) ESR meter

Thanks, all, for the nice comments.

The cardboard is from some random package I received. The flaps are stuck down with generous amounts of PVA glue [poundland!] (held in place with masking tape until they dry. When all the internal flaps have been stuck, another load of PVA goes on the outside of the joints (+ is left to dry). Finally, yacht varnish (2 or 3 coats) is applied to the outside. This really does improve the rigidity (+resilience of these boxes). hot glue is used for mounting things inside the box.

I had one with a home-made radio in for ages (literally, decades), before the NiCad battery in it finally wouldn't hold a charge.

I also have many surplus meters so it's nice once in a while to use one rather than the becoming-ubiquitous 16x2 LCD displays or mini LED voltmeter displays.
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Old 21st Nov 2022, 7:17 pm   #7
Bazz4CQJ
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Default Re: (another!) ESR meter

When the PVA soaks in to the cardboard, you're really creating a matrix material and then coating that with varnish takes it one step further.

In the absence of cheap ali boxes, I thought I would try my hand at the art of tin-smithery, and bought a small sheet from a model shop, but have not yet used it. I'm planning to use some tin plate in the QST Rx. I had an old friend many years ago who was magic with tin plate. The instrument boxes that came out of his cellar were indistinguishable from something off a factory production line.

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