ESR meter - project

blueroomelectronics said:

Build it as specified, then try to simplify it. Your version does not even appear close. Why would you not build it like its original design? It's only one IC afterall.

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blueroomelectronics said:

The one from the other forum that you link to in this thread, and until you hand wire a small prototype it's jumping the gun to design a PCB for it. It may not work.

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ljcox said:

Sorry, I forgot to post my circuit. Here it is. The .pdf includes a circuit description.

I made it on a prototyping PCB that I purchased from JayCar.

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• The oscillator part (IC1a, P1, R8 and C1) that generates 200Khz, can it be replaced with the popular 555 ic as long its configured to generate same 200 Khz pulse ?
• Can this circuit capable of probing an "in-circuit" cap ?
• How much voltage approximately that is applied to the DUT during the test ?
• About the gain for the LF411 op-amp, with the current amplification it will represent 100 mV to the dmm when the dut is at 10 Ohm, is it possible to increase it 10 times, say 1 volt at 10 Ohm ? So it will be easier to use with those dmm that has only 200mv with 0.1 mV as the lowest resolution.

BravoV said:

I'm aware of bumping a really old thread, but already contacted ljcox this circuit designer to respond here.

Few questions about this circuit :

• The oscillator part (IC1a, P1, R8 and C1) that generates 200Khz, can it be replaced with the popular 555 ic as long its configured to generate same 200 Khz pulse ? Yes or the 7555. Note that the 555 consumes a lot more current than the CMOS ICs.
• Can this circuit capable of probing an "in-circuit" cap ? Yes.
• How much voltage approximately that is applied to the DUT during the test ?
  About 0.7 Volt peak or 1.4 V pp. This is set by diodes D1 & D2.
• About the gain for the LF411 op-amp, with the current amplification it will represent 100 mV to the dmm when the dut is at 10 Ohm, is it possible to increase it 10 times, say 1 volt at 10 Ohm ? So it will be easier to use with those dmm that has only 200mv with 0.1 mV as the lowest resolution. See below.

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MrAl said:

Hi again,

Oh, so ljcox asked you to post here to ask questions about the circuit?

I'll hold off on my suggestions until ljcox has a chance to reply here.

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ljcox said:

The gain is set by the ratio of R11/R10. So if you want 10 times the gain, change R9 & R10 to 270k.

I have attached a table of ESR values. I don't recall where I obtained this info, so it may be a bit out of date now.
Len

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ljcox said:

Sorry, what I wrote in red is a bit misleading.

What I meant is that the maximum voltage that can be applied to the DUT is about +/- 0.7 Volt.

But that would only occur if the DUT had a fairly high ESR or was open circuit.

If you apply Ohm's Law to the string of resistors R1, R2, R3 & ESR (during a negative half cycle) & assuming that the ESR = 10 Ohm, then the current is approximately 2.1 mA.

Therefore the voltage across the DUT will be about -21 mV and the voltage at the anode of D2 will be about 166 mV.

The diodes are to limit the maximum voltage that can be applied to the DUT & to protect the ESR Meter against the possibility that it may be inadvertently connected to a charged capacitor. See the circuit description for more detail.

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whiz115 said:

ok i listened to your advice and i did a prototype with a PCB layout i found on this site:
https://www.yoreparo.com/foros/diseno_electronico/80575.html

(use an online translator to translate the site to English)

The PCB layout i think it's the original schematic of Nuova Elettronica... and it is not exactly the same as the schematic in the previous page which it is supposed that it is improved and behaves better than the original design.

The prototype works but I used resistors of whatever tolerance i had in front of me and i don't know if that affected the way it works, i don't think that it does what it is intended to do... if you short the test probes it outputs 120uA and with most capacitors it also outputs 120uA in few cases it shows different values...the trimmer pot just lowers the output uA but doesn't give full range on my analog multimeter although i have it in the lower scale.

probably i should try some other ESR meters like ljcox's from the previous page... but none of them has PCB layout and it is overkill for a newbie to build it.

i don't know what to do now... should i change resistors with more accurate? or i should forget it? any ideas?



P.S if someone wants to see it i can upload photos...

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ljcox said:

The gain is set by the ratio of R11/R10. So if you want 10 times the gain, change R9 & R10 to 270k.

Len

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whiz115 said:

I have found many but some of the designs probably are copyrighted and i don't know which one i can post and which i can't.


recently i tried to convert one of them into PCB... it's a improvement some guy did...based on a design which belongs to Nuova Elettronica.

**broken link removed**


(This is the improvement and not the original which exists on an other forum. The original can also be found online)


**broken link removed**


and this is my unfinished try on Eagle to convert the above into schematic and then PCB.

it's my first time on Eagle it's total mess right? can someone give me instructions what to do?

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mvs sarma said:

I remember that there were updates with corrections for the siliconchip2005 article perhaps same article was also published in epe magazine.

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