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my project not working

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peter g

Member
hi members, I just completed a esr meter project. the title as it appears on the internet is CAPACITOR ESR METER WITH TONE. the problem is the meter does not deflect. the 100khz osc is running. the signal gets as far as U2A pin 1. the signal at pin 1 varies between 2&3 vpp. its jumping up and down. that's where every thing stops. plz help. d3 and c6 are good.

http://www.qsl.net/kh6grt/page4/esrmeter/esrmeter.htm
 

mvs sarma

Well-Known Member
hi members, I just completed a esr meter project. the title as it appears on the internet is CAPACITOR ESR METER WITH TONE. the problem is the meter does not deflect. the 100khz osc is running. the signal gets as far as U2A pin 1. the signal at pin 1 varies between 2&3 vpp. its jumping up and down. that's where every thing stops. plz help. d3 and c6 are good.

http://www.qsl.net/kh6grt/page4/esrmeter/esrmeter.htm
Did you use tantalum caps for the polarized ones at C6, C7, C9 and C10? if so , please check polarity reversal by accident.
secondly check for the pot centre pin looped to one side for R19 If the pot under concern is 10 turn bourns type , the pin out is different against normal ones. the back last pin is centre tap.
 

peter g

Member
hi Sarma, is it possible there is not enuf gain to switch d3? don't know why waveform on pin1 u2a is jumping up and down.
 

dr pepper

Well-Known Member
Most Helpful Member
If you lift one end of these 3 resistors, R15, R37 and R23 you'll have just the meter circuit operational, the tone and short led will be out of circuit starting with this might give you some idea where the issue is.
Check to make sure D3 and D4 are ok and in the right way around, check to see if the meter is still ok and not blown open, a mulitmeter on ohms will make it deflect, probably all the way.
That design looks very good, however there is one big drawback I see, the meter zero adjustment, its possible to adjust it so that you have zero ohms between the op amp and meter movement, this would risk blowing the movement, I suspect this has happened with yours.
A 22k inline with the zero pot is a good idea, this would limit the max current through the meter to about triple its rating for 100uA.
 

peter g

Member
no, the meter reads about 1600 ohms, so not open. when I put 1-2volts on the k of d3, it seems to work. meter deflects and can be controlled with the pot.
 

dr pepper

Well-Known Member
Most Helpful Member
Something odd is happening, if you have that voltage at the op amp o/p theres only the 2 diodes and zero pot inline with the meter, if these parts and the meter are ok you should get deflection.
When you checked the meter's resistance did you look too see if its pointer moved?, maybe its jammed.
Edit: i just had another look at the schem, the author is generating a artificial ground with U5, check to make sure this has an o/p of around 1/2 the battery voltage, if this isnt working properly the then all the op amp o/p's could well just sit at ground or V+.

The peak detector works via D3, it only allows the positive side of the waveform through to C6 whci is then charged up to the peak voltage via D3 and the op amp U2a, the chrage decays away slowly through the meter.
 
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peter g

Member
yes, sarma I used 1% res. the meter did deflect when I measured the res. what makes d3 conduct and how do peak detectors work?
 

peter g

Member
I have plus and minus 4.6 volts on pin 4&8 of opamps. how high does the pos peak need to be at the anode of d3 for it to conduct?
 

mvs sarma

Well-Known Member
i get your question,

Incidentally,for adding text to previous post of yours , perhaps you can click edit and add text and save the changes.

Back to U2a, i suppose it is half wave rectification and not peak detection. with full feed back (means unity gain for positive peaks.) The output would be only positive pulses with a drop of say 0.65V or so (that of Diode)

PS: let me read the description part w.r.t the sch
 

dr pepper

Well-Known Member
Most Helpful Member
To clarify what Mvs just said, there will be 0.6v across the diode, however because D3 is in the feedback loop of the op amp the 0.6V can be pretty much ignored, the o/p voltage across C6 should be 1/2 of the peak to peak waveform at the i/p U2 pin 3 (due to the cap C5).

So your power rails are ok.

I'm finding it odd that you have Volts at U2a o/p but the meter dont move when theres only a pot and a diode between that point and the meter.

Try disconnecting the meter from the circuit and connect it to a 1.5V battery with a 33k resistor in series, doesnt matter which leg - or +, if the meter is good it will deflect to very approximately 1/2 way.
 
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peter g

Member
its so frustrating, its such a simple circuit. the sine wave at the o/p of u2a does fluctuate, don't know whats causing that. I read no voltage at the k of d3? i'am going to change d3 and c6 though they both check ok.by the way, thanks so much to you guys for helping.
 

peter g

Member
yes, I did. I used the toner transfer method. btw, I couldn't source the kia75558p, so I used lm1458 instead.
 

audioguru

Well-Known Member
Most Helpful Member
The LM1458 is a dual 741 opamp that was designed 48 years ago. Its spec's show ONLY a 30V supply so many of them will not work with your 9V battery and it has trouble with frequencies above only 9kHz.
I think the original circuit in QST magazine used TL081 opamps that are MUCH faster than an old LM1448.
Use an opamp with more modern spec's.
 

audioguru

Well-Known Member
Most Helpful Member
An OPA134 single, OPA2134 dual or OPA4134 quad opamp from Texas Instruments is a good low noise, low distortion audio opamp. Its supply can be from plus and minus 2.5V to plus and minus 18V. It works well to to 220kHz.
A TLE2141 single, TLE2142 dual or TLE2144 quad opamp also works with a low supply voltage and works well up to 400kHz.
 

peter g

Member
thanks for the information. I will get those opamps and give them a try. i'am wondering thou, wouldn't the fact that there is 2.7vpp at the anode of d3, proof that those op amps are working. the freq is 71khz?
 
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