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Old 12th Aug 2010, 5:56 pm   #21
David G4EBT
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Default Re: My Homebrew ESR Meter for testing el caps

R10 - shown on the circuit as 25k is not a preferred value, which is why I used a 22k. It's role is for adjustment to get FSD on the meter, and is in series with R17, which - as I stated, is 10k on the circuit, but which I found I had to reduced to 3k3 to enable the meter to adjust to FSD.

Either or both of these values may need to be altered by experimentation depending on which type of 50uA meter is used, if a different one is fitted from the ESR Electronics one that I used. The values aren't critical, so long as you can achieve FSD with the test prods shorted.

BTW, to calibrate the meter dial requires only four low value resistors - eg, two 1R in parallel = 0.5R, one on its own = 1R, the two in series = 2R. Then 2 x 10R in parallel = 5 R, then added to the 1R resistors, = 6R, 7R, and a 10R on its own = 10R. (8 & 9 R can be inferred between 7 -10). I calibrated the scale on my meter up to about 15R, which took up about two thirds of the scale but most good caps will have an ESR of just a few Ohms. I'm away from home just now, but IIRC, about a third of the scale went to 5R, then the next third up to 15R. After that, it's irrelevant.

Hope that helps.

David
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Old 13th Aug 2010, 10:20 pm   #22
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Default Re: My Homebrew ESR Meter for testing el caps

A most interesting thread that has stimulated me to start building this ESR meter.

Years back I used to repair computer monitors and switch mode power power supplies for a living. An ESR meter was a must. Then I used a Capacitor Wizard with a analogue display, then after I killed it, a Bob Parker designed ESR meter kit from Dick Smith Electronics in Australia. That eventually died too. I no longer need one for my work, but do for my hobby.

Steve
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Old 16th Aug 2010, 6:26 pm   #23
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Default Re: My Homebrew ESR Meter for testing el caps

Hi David (G4EBT),
Just to double check - am I correct that with the inclusion of the regulator Q2, you have ditched the 10uF electrolytic?

Best Regards

Rob
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Old 18th Aug 2010, 8:51 am   #24
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Default Re: My Homebrew ESR Meter for testing el caps

No - it's still there. All I did was to add the 5V regulator and amend the PCB layout slightly to accommodate it. If you compare the pic of my PCB and that of pic of the designer's original layout, you'll see that the 10uF tantalum cap (C7) is present.

Hope that helps.

David.
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Old 22nd Aug 2010, 10:45 am   #25
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Default Re: My Homebrew ESR Meter for testing el caps

Thank you all for this forum entry. I am trying to build this meter myself. I have a buddy that is helping me because he knows much more about electronics than I do.

My issue is in ordering the parts. What is the type of capacitor used at C5? The .47uF 400V capacitor. Is it a 'film capacitor'? Also, what is the voltage of the other capacitors required for the board? 10V, 16V, 25V? I just don't know what to purchase. The last thing is that I know this meter will help me to find bad components on a board without randomly replacing things. Can someone create a parts list for this design? It would have helped me order these parts much sooner.

Thank you all again. I will update this thread with my completed design. David G4EBT, your project box turned out very well. Later...
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Old 23rd Aug 2010, 8:45 am   #26
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Default Re: My Homebrew ESR Meter for testing el caps

Firstly, I'd like to reiterate that I claim no credit for the design of this useful bit of test gear – the credit must go to the designer - Lawrence P Glaister, VE7IT - a Canadian radio amateur. The list of parts is self evident from the circuit, but I’ve received several queries, including queries about 'missing' caps and resistors, so this list and notes about the components might help others who may be contemplating building this device:

Parts list:

R1 – 1k0
R2, R3, R4, R5, R6 - 680R
R7, R8 - 10R
R9 - 100k
R10 - 22k (25 k specified)
R11 - 2k2
R12 - 100R
R17 - 10k
R18 - 1M0 0.5W

Apart from R18, the other resistors could be say 1/3 watt, but 0.5 Watt metal film or carbon film resistors (as sold in the UK by ESR and others) cost only a couple of pence each.

Zero pot to set FSD: 22k. (25 K specified – see note below)

Note: There are no resistors marked R13 – 16 in the circuit, which uses a total of fourteen resistors, as listed above. I can only assume that the prototype had more resistors, and the author didn’t re-number the resistors in the final version.

The author specified 25k for R10, which is not in the more common E12 series of resistors, so I used a 22k, which seems fine. Similarly, for the FSD meter adjustment pot, the author specified 25 k, but this isn’t critical, and 22k will be fine. In any event, that pot is in series with R17, stated as 10k, though in his update, the author says he had to later modify that to 4k7. I had to drop this to 3k3 to get my meter to go to FSD. The important thing is that the combination of R17 and the pot must enable the meter to be set to FSD with the test prods shorted. (Zero Ohms). (The zero pot isn't actually shown on the circuit - it needs to be fitted between TP 3 and the meter + connection).

Capacitors:

C1,C2,C3 - .01uF
C4 – 0.047uF
C5 - 0.47uF 400V DC Isolation Cap. (See note below)
C6 - 0.1uF
C10 - 10uF Tantalum 16V

C5 is there to protect the meter from the stupidity of a user who might connect the prods to an undisharged high voltage electrolytic cap, such as a smoothing or reservoir cap in a valve radio, and zap the meter. It goes without saying that for personal safety, anyone working on high voltage equipment - even when disconnected from the mains - should always discharge electrolytics before delving into the set. Should this not be done, at least the ESR meter will be protected, if not prying fingers.

The other caps can be miniature resin-dipped ceramics, which are usually rated at 100V, but anything over 10V should be fine. (As with the resistors, there are some gaps in the list – there are no caps C7, 8 & 9).

IC1 – 74HC14N
Q1 – 2N2222 NPN transistor.
D1,D2,D3,D4 – 1N1418
D5, D6 – 1N4004.
78L05 5V+ 100mA regulator (If following the mod that I included on my updated PCB layout)

M1 – 50uA analogue panel meter

Other bits:

PCB (or plain matrix board, with component leads connected along the lines of the PCB track layout beneath the board).
IC socket
Croc clips for test leads
Case
On/off switch.
PP3 battery connector.
Project box, wire etc.

I also included an LED, with a 470R series resistor to show when the meter is switched on. (A needless refinement I guess, but this is, after all – ‘homebrew’!)

I can't suggest overseas suppliers, but all of the above items are available from many UK suppliers, including ESR Electronics, who have no minimum order level or minimum pack size, and charge only £2.50 P&P. Their current catalogue can be viewed and downloaded from here:

http://www.esr.co.uk/

(I have no connections with ESR other than as a satisfied customer).

The total cost of components - including the meter movement, should be no more than £10.

I hope these notes, together with earlier postings, answers any outstanding queries.

Best of luck.

David
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Old 24th Aug 2010, 6:41 am   #27
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Default Re: My Homebrew ESR Meter for testing el caps

That was perfect. The only thing left I could ask of you is to build one, send it to me, and I will use that as an example for my own build. Kidding! That list is nice and complete. The parts list that G4EBT can also be purchased in the United States via Mouser.com or Digikey.com Both sites will have the parts needed. My parts run down from Mouser is less than $20 dollars including shipping. Amazing! The shipping is actually the highest cost item. When mine is complete I will write a 'build' thread on this. Including P/N's and so forth.

Thanks again,
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Old 24th Aug 2010, 8:46 pm   #28
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Default Re: My Homebrew ESR Meter for testing el caps

Does anyone know how to adapt the esr meter to measure the esr of a battery? I remember reading somewhere that all you had to do was omit the 2 diodes across the test terminals (and possibly reduce the WV of the 470nF cap to take up less room on the board).

Most "enthusiasts" building this meter will have most of the components in the scrap box (saving the pennies) and the only bits needed would be the meter, the IC and the case. Just remember to use a socket for the IC - it saves a lot of grief if you have a bad soldering day!
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Old 5th Sep 2010, 6:27 pm   #29
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Default Re: My Homebrew ESR Meter for testing el caps

This is the Vero Board arrangement I used. Having a spare RS 259-561 100uA edge-meter I used this though I had to leave out R17 to get enough meter drive, still using a 22k series pot for setting zero. Note I used a SIL resistor pack for R2-R6, the type with all resistors connected to pin 1. I had planned to fit C5 off board but at the last moment decided to mount it as shown. At least all the components are together along with R18 and it leaves just the wiring to worry about. You will note that I also opted for the 78L05 design.
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Old 5th Sep 2010, 9:40 pm   #30
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Default Re: My Homebrew ESR Meter for testing el caps

Very neat job Topcap - and the drawing too!

(What software did you use to draw the layout with please?)

The Vero layout should encourage those who may have been put off by the PCB version to have a go. An ESR meter has to be one of the most useful and cheaply made bits of homebrew kit that there is.

Re R17, I think that's very much a 'select on test' item, with whatever meter is used, to get the meter to read FSD. I guess the best option is to temporarily put say a 10k preset in the position of R17, and with the 22k series pot in line, to adjust the pre-set to get FSD on the meter, then measure the resistance of the preset and select a resistor of that value as R17 - unless of course, it needs to be left out altogether and a link substituted for R17.


David
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Old 5th Sep 2010, 11:26 pm   #31
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Default Re: My Homebrew ESR Meter for testing el caps

Hi David, for drawing I just use Paint, having acquired over time separate libraries of parts like, Vero board, circuit diagrams, mechanical drawings etc. One major reason for this is that my company will not allow me to install any personal CAD software on the works PC's and conversely will not allow me to have a copy of theirs. This I found restrictive if I wanted to knock up something work related at home but of course Paint is free on all PC's so it avoided any such problems. After running the ESR Meter this evening, I decided to remove the pot as I don't think the zero setting will move much with a stabilised supply, making R17 4k7 to match my meter. I just went through one tray of electrolytics and found three faulty ones. One gave just a quarter reading.
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Old 6th Sep 2010, 10:41 pm   #32
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Default Re: My Homebrew ESR Meter for testing el caps

The graphics are certainly impressive - once more, underlining a gap in my 'skills portfolio'! Re R17 - good point, with the 5V regulator mod, once the FSD is set by choosing a suitable resistor, that should be it, without the need for a front panel pot.

Glad to heat that your meter is working and already earning its keep in sorting the 'wheat from the chaff' among your el cap assortment!

David
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Old 8th Sep 2010, 10:56 am   #33
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Default Re: My Homebrew ESR Meter for testing el caps

Hi,having a little trouble sourcing C5-470nf 400v cap.I can find these in poly,will they do? Andy.
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Old 8th Sep 2010, 5:39 pm   #34
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Default Re: My Homebrew ESR Meter for testing el caps

The function of C5 is as a safety feature to isolate the ESR meter circuitry to prevent it being zapped by HV DC if you inadvertently connect it to an undischarged HV electrolytic such as a smoothing cap, or - perish the thought - to a live one. For personal safety, as a matter of course, we should always discharge HV caps before connecting anything to them, especially fingers!

To that extent, so long as the cap is 400V or more, I don't see that the type is critical, and in normal use, applied to an electrolytic cap under test, the cap should have zero volts on it, provided it's been discharged.

(Incidentally, provided that a cap has been discharged, there's no need to remove it to test the ESR - that can be done whether the cap is in or out of circuit)

Hope that helps.

Best of luck Andy.

David
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Old 17th Sep 2010, 7:07 am   #35
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Default Re: My Homebrew ESR Meter for testing el caps

The ESR Meter is great for testing capacitors but the need to desolder a single lead may still be necessary. The actual testing of a capacitor while still in circuit can be tricky. I found a YouTube video located at this address: http://www.youtube.com/watch?v=GZMQWa0b1xY It is presented by John Preher from Preher-Tech.com

I have chatted with John and in watching the video it is important to ensure that if you have capacitors in parallel that floating a single pin from the capacitor being tested is VERY important. You can absolutely receive a false result from your meter due to conductances.

Please take a look at the two videos he has regarding the testing of capacitors. They were extremely informative to me and may be to some of you who are not well versed in electronic components as is the case with me.

I learned something there that will be very helpful to me in the future. Though I don't understand everything that he spoke of, he did get the point across on the myth of an ESR meters ability to test any capacitor while in circuit.

Take care...
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Old 26th Oct 2010, 11:25 am   #36
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Default Re: My Homebrew ESR Meter for testing el caps

This design, by Canadian amateur VE7IT, has proved to be a popular and useful project, many having successfully been built. I've had a great deal of feedback, on which these notes, updating the PCB layout, are based.

I'd reiterate that if all the items are bought new it ought not to cost more than £10.00 (excluding the cost of a box in which to put it). There are no hard to get components and unlike some designs there is no transformer to wind. The only adjustment needed in setting up is to set the meter to full scale deflection with the test prods shorted. The dial can then be simply calibrated with half a dozen low value resistors.

In another post I’ll write some notes might help less experienced constructors to build the project and if need be, how to troubleshoot and get it working, and how to calibrate the meter dial. I’ll include in that post some ‘scope traces of what to expect at various points.

For those who are unable to make their own PCB, an excellent Veroboard layout has been designed by ‘Top Cap’ at post 29 of this thread, but for those who are able to make a PCB, to make building the project a little easier to build, I’ve updated the PCB layout based on feedback I’ve had from forum members.

I’ve attached the updated layout, and an x-ray of the PCB showing the component overlay with the amendments highlighted. All other component placings are as per the original layout. (Do remember that the layout is as it must appear on the etched PCB - if the press ‘n peel or laser ‘photo print/iron-on’ method is used, the layout must be ‘flipped’ or the PCB will come out back to front!).

In summary, the amendments I’ve made to the original version are:

1) 5V 0.1A voltage regulator added to enable the use of a 9V PP3 battery:

In the original design a front-panel mounted pot was necessary as the designer used rechargeable cells to power the meter. The IC used (74HC14N) will work at voltages between 2 to 6V, but by using rechargeable cells - which fully charged will be 4.8V, and will self discharge even when the meter isn’t used - required that the meter be adjusted from time to time to get it to read FSD with the test clips shorted.

I preferred to use a 9V PP3 battery rather than rechargeable cells, so from the outset I altered the PCB layout to include a 0.1A 5V TS78L05CT regulator so as enable a PP3 to be used.

2) A 22k sub-min pre-set pot mounted on the PCB instead of a front panel pot:

Some constructors were unclear as to how to connect the meter movement and the FSD zero pot to the PCB. The inclusion of the 5V regulators means that once the meter adjustment pot has been set to give FSD on the meter with the test leads shorted, it ought not to need adjustment again, and should continue read FSD until the battery expires. (The meter only draws a few mA, and is used only briefly, so a PP3 should last a long time).

Hence, a front panel mounted pot isn’t needed, so I’ve modified the PCB layout to enable a vertical preset pot to be mounted on the PCB. This removes any complications in wiring the pot and meter movement, which now needs just two connections from the PCB.

3) Provision for an LED supply from the 5V rail, with an on-board series limiting resistor:

An LED is a useful addition as a warning that the meter is switched on, so I’ve amended the PCB to include an on-board series limiting resistor for the LED from the 5V line. Hence, all that’s needed is two wires from the PCB to the LED.

The value of the series LED resistor will depend upon the characteristics of the actual LED used, (its forward voltage and current) but generally, a 330 Ohm resistor should be fine. If the LED looks too dim, reduce the value of the series resistor progressively to 270R, 220R etc.

For the curious, if the characteristics of the LED are known, there’s a series resistor calculator for LEDs at this link. All you need to do is to input the supply voltage, the LED forward voltage, and current. It then tells you what the nearest preferred value series resistor you need to choose:

http://led.linear1.org/1led.wiz


4) I’ve provided an extra pad on the PCB for the 0.47uA 400V capacitor C5, to enable two sizes of radial lead caps to be accommodated as well as an axial lead one. Use whichever pad is needed.

I’ve previously stated that the value of R17 - the series meter shunt, needs to be reduced from the original 10k down to 3K3 or it is unlikely that the meter will reach FSD when zeroed.

A table written by ESR meter guru Bob Parker, of approximate worst-case (highest) ESR values for new electrolytic capacitors at 20 degrees C (68'F) can be found at this link:

http://www.your-book.co.uk/design/esrchart.htm

Or here:

http://members.ozemail.com.au/~bobpar/2003esrchart.txt

I hope these notes and the updated PCB are of help to anyone contemplating building this useful little project. Once again, I must make it clear that I claim no credit for this design – all that I’ve done is to tweak it to my own requirements in the spirit of home-brew and experimentation. The credit for the original design must rightfully go to a Canadian radio amateur - Lawrence P. Glaister, VE7IT. The link to the original article can be found here:

http://www.members.shaw.ca/swstuff/esrmeter.html

As a footnote, the designer referred to the oscillator (gate 1 of IC1) frequency 150kHz, and the circuit shows 156kHz, though neither of these are correct, given the values of C1/R1. As far as I can determine, the formula for calculating the oscillator frequency of the 74HC14N is 1/C1*R1= f MHz, where C1 is uF and R1 is Ohms.

Hence: 1000*.01 = 10. and 1/10 = 0.1MHz = 100kHz.

Having tried several 74HC14 ICs from more than one maker, they all come out at around 100kHz. The actual frequency has no bearing on the accuracy of the meter, and in fact 100kHz is the frequency that many designs seem to operate at. (Using this formula, a frequency of 150 KHz would require R1 to be 665R, and at 156 KHz, 640R)

I mention this only in the event that a curious constructor with a frequency counter might decide to check the actual frequency at pin, and finding that it’s near enough 100kHz rather than 150/156 kHz, might wonder if it’s faulty.


I hope these notes, togehter with those in another post outlining the setting up and troubleshooting, are of help and encouragement to anyone contemplating building this handy and cheaply made little project.

David
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Old 26th Oct 2010, 11:45 am   #37
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Default Re: My Homebrew ESR Meter for testing el caps

ESR meter construction and testing notes.

These additional notes, based on help that I've given to several constructors who have had teething troubles building the meter, might help less experienced constructors to build and set up the project, and if need be, to troubleshoot and get it working.

As with all projects it’s important to check that components are the correct value, particularly those which have obscure markings. Even resistor markings aren’t so straightforward these days - often using the 5-band marking code, as at Maplin for example. Also, ensure that diodes are connected the right way round.

The 2N222A transistor comes in two case styles, the more common of which is the metal ‘TO18’ style case. It also comes in the plastic TO92 case. On the ‘x-ray’ picture of the PCB, in my other posting, which shows the updated PCB, I’ve shown the pin-outs of each case style.

A word of warning though – there are less common TO92 cased 2N222A transistors in which the emitter and collector are reversed. It’s therefore wise to use a metal cased one, or to check the connections on a transistor tester to be sure.

Setting up and troubleshooting:

Initial tests and setting up:

On completion of the project, set the meter adjust pre-set pot on the PCB to midway position, and before inserting the IC, switch the meter on, and check that there is 5V present at pin 14 of the IC socket. (Black test prod to pin 7 of the socket – red to pin 14). If all is well, insert the IC, short out the test prod leads, and the meter needle should deflect to the right. If so, adjust the preset pot on the PCB until you get full scale deflection on the meter. It should not need adjusting again.

Calibrating the dial:

Having zeroed the meter with the pre-set pot so that with the test prods shorted it shows full-scale defection - zero Ohms, you can begin calibrating the dial using a few low value resistors as follows:

Two 1 Ohm resistors in parallel = 0.5 Ohm, one on its own = 1 Ohm, two in series two Ohms, then more 1 Ohm resistors up to 10 Ohms, and so on. On the 50uA meter that I used 1 Ohm was about 80% of full scale, 5 Ohms mid-scale, 15 Ohms about 30%. Really, any cap approaching 10 Ohms is highly suspect, so it’s the low Ohms end we’re interested in, at the RH end of the scale.

What if it doesn’t work?

Carefully check all the components, especially the correct orientation of the diodes, Q1, the voltage regulator, the IC and C7 (the only polarity sensitive capacitor). Using a magnifying glass, check for any solder bridges - for example between the pins of the IC socket. Check that you have 5V+ at pin 14 of IC1. If not, is there 9V at the input of the voltage regulator? If so, suspect the regulator. Check that you've used the right IC - 74HC14N. (Not 74HCT14N).

It helps if a scope is to hand to check the waveform at various points, and to gain an understanding of the various elements of the circuit. The IC is a hex Schmidt trigger. One of the six gates, along with C1 and R1 form an oscillator circuit, which is as simple as an oscillator gets. The values of C1 and R1 determine the oscillator frequency, which the designer states as 150 or 156kHz, but is in fact nearer to 100KHZ, though this isn’t critical and has no bearing on the accuracy of the meter.

All ESR meters work on a similar principle - the application of a low amplitude AC signal usually of a frequency between 100kHz - 200kHz, to the capacitor under test. I’ve tried various 74HC14N ICs in this design and they’ve ranged from 100 – 105 kHz. More about that in the footnote. (The ‘N’ suffix simply denotes a 14 pin DIL package. Any prefix denotes the ID of the maker. In the family of the '74' series of ICs the 'HC' stands for
High Speed CMOS with CMOS-compatible inputs).

Pin 2 of IC is the output of the oscillator, which goes to the input of the other gates at pins 3,5,9,11 & 13. The outputs of those five gates at pins 4,6,8,10 & 12 go to the five 680 Ohm resistors R2,3,4,5 & 6, and form a buffer and Low Pass filter. At the junction of those resistors, which are all coupled together on their outputs, there should be a waveform of approximately 250mv peak to peak at about 100KHz.

The next stage is the input protection stage (D5, D6, C5 etc) which protects the meter from damage should it get zapped with an un-discharged capacitor attached to the test leads.

From the junction of R8, D5, D6 and C5, there should be a waveform of about 180mV peak to peak, but it’s important to note that this is only when the test leads are shorted, or a good cap with a low ESR is connected to them. This AC waveform then passes via C2 to the base of the 2N2222A which is an AC amplifier with a gain of approx 10.5.

It's role in life is to raise the 180mV p-p input to nearer 2 Volts p-p. This then passes to the meter rectifier D1,2,3 &4, for the meter movement. But without the test leads shorted, or a known good electrolytic cap with a low ESR attached to the test leads, there will be zero Volts at the input of the 2N2222A, nothing at its output, so no deflection on the meter.

The meter rectifier enables the meter to function as an expanded scale AC voltmeter. Full scale is zero Ohms, midscale is approx 10 Ohms. There is no DC output until approx 75 Ohms of ESR is seen at the test terminals, (ie, a bad cap), at which point the meter will barely deflect.

Getting the meter to read Full Scale Deflection:

The original circuit specified a 10k resistor for the 50 uA meter shunt, (R17) though the designer refers to having to reduce that to 4k7. I found that I needed to reduce it still further to 3k3.

New 50uA meters can be found cheaply on internet, though often with a small face. The one that I used is 60mm x 46mm and was supplied by ESR Electronics Ltd, Order Code 124-116, current price (Oct 2010) is £5.54 + £2.50 + VAT: http://www.esr.co.uk/electronics/pro..._testequip.htm

(Tel: 0845 2514363).

I have no connection with that or any other commercial outfit.

That the firm's name is 'ESR' Electronics is purely coincidental, but rather apt!

I’ve attached some pics to show the waveform at various parts of the circuit in a working model (with the test leads shorted). There are:

1) At pin2 of IC1 - the output of the waveform generator, (which simply consists of one resistor, one cap, and one gate of the hex Schmidt trigger IC).
2) At the output of the buffer/Low pass filter (junction of R2-R6)
3) At the base of Q1
4) At the collector of Q1

I hope these notes prove useful, and an encouragement to anyone contemplating building this useful little gizmo, and I do hope that these notes haven't made it sound a lot more complex than it is. It's actually an ideal first homebrew project.

Best of luck!

David.
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Old 27th Oct 2010, 12:34 pm   #38
valvekits
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Default Re: My Homebrew ESR Meter for testing el caps

Thanks for all the effort you have put into this David. By the way, the interest in this project has seriously depleted the stock of the 50uA meter held at ESR and the next batch won't be in until mid-November.
Cheers
Eddie
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Old 27th Oct 2010, 2:17 pm   #39
Guitarist28
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Default Re: My Homebrew ESR Meter for testing el caps

Hi David,
Well done on your update thread for this as having read through this the project is now very straightforward and as you say and ideal beginner project.

Regards

Rob

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Old 23rd Nov 2010, 11:02 am   #40
David G4EBT
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Default Re: My Homebrew ESR Meter for testing el caps

Several would-be constructors have advised me that the 50uA analogue panel meter that I used in this project has been out of stock for some while at ESR Electronics Ltd.

I've checked with ESR Ltd this morning when ordering other items and they advise me that the meters are now back in stock and that they have plenty. ESR aren't of course the only suppliers of 50uA meters, but the one that they stock has a 60mm x 46mm oblong dial, which is larger than the more commonplace 40mm square panel meters, so is clearer to read when a scale showing ESR readings is fitted.

The ordering code for the meter is: 124-116.
The current price is: £5.54+£2.50 P&P + VAT
The description is: 0-50uA Panel Meter.

The link to the item is:

http://www.esr.co.uk/electronics/pro..._testequip.htm

Tel: 0191 251 4363

I'd re-emphasise that I have no connection with ESR or any other commercial organisation, other than as a satisfied customer. Just trying to be helpful.

(It's purely coincidental that the firm has the same initials as the project - 'ESR').

Best of luck to anyone who is still contemplating making this useful little gizmo.

David.
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