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This is really annoying, I just want to hit myself, I don't know why I desolderd the two Tl081CN's and put Tl071CP, now the device give only single beep when I connect the coil but it give no reaction at all, before it was working and now it is not, I measured the voltage at U104 pin6 it was 6v and at U105 pin6 it was -5.35v, even if I remove the coil but these points voltages still the same, is that normal?, I even placed back another new Tl081 but the one ends with CP not CN as it was before,but the problem still the same, is there any difference between Tl081CP and Tl081CN?
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I swear if I can ship a metal detector to my country I would did that long time ago instead of making one,the government forbidding such devices here,I'm really tired, anyway, waltr can you check these points at pin6 with and without the coil and tell me what you get?Comment
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Originally posted by waleed View Post
I tried checking some data sheets and can only conclude that one maker uses CN and other uses CP for the 'same' part.
What manufacture made these?
Opened the TGSL schematic and the outputs from U104 & U105 pin6, should be very close to Zero Volts. These I am sure of since they go to the compactor.
The Negative Voltage can only be there IF the TX coil is connected to have the Oscillator and then the Charge pump running.
If you have -5V without the TX coil check the oscillator.
Are you sue you didn't put these op-amps in backwards??
I did this when I first built my TGSL. The orientation on the PCB can be in any direction so easy to get chips in backwards.Comment
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I'm sure I placed them correct,I even put back a new Tl081 but CP not CN, but the problem is the same, I'll try the Tl081CN and I'll see, I have negative 6 volt when I connect the TX coil as normal, I checked everything on oscilloscope and everything was good (disc and GB channels and the oscillator and the changing pump), but I don't know why I have 6v and -5.4v on the output of the Tl's,when I disconnect the TX the output voltage becomes in millivolte.Originally posted by waltr View Post
Are you sure the output on the Tl's is zero volte when you connect the coil and without moving any target?, can you check it, btw I checked the ampere of the entire circuit it was 150mAComment
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You are in luck. My TGSL is still open and the scope is on.
Yes, both outputs are 0V with a +-100mV 60Hz (due to AC mains interfere inside the house).
If I wave my ring near the coil signals go to several Volts.
The op-amps I used are TI TL081ACP. I also have some TITL081CP.
The TI data sheet has both CP & CN as plastic 8pin DIP package. One comes in 50 peice tubes the other in 25 piece tubes with no difference in specs.
The CP & CN have a max Vos of 15mV whereas the ACP's max Vos is 6mV.
Without the coil connected both have Zero Volts at output an no AC mains noise.
Re-check everything especially soldering. Use Ohmmeter and check for shorts and also connections to other part.
It must be something simple.Comment
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The -+100mV you measured is DC right?, waltr when I overlap the coils the device gives acontinues beeping at a specific point and when I move them a bit the sound is gone, do you know what, I believe that the problem is not with Tl's, the continues beeping that appears sometimes when overlapping indicates that the problem is with a certain diode, maybe I damaged a diode that near one of the Tl's when I desolderd them? I think I applied much heat when I was desoldering, is that possible?.Originally posted by waltr View PostComment
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Oki I removed the diodes near the two Tl's and check them,they are working good, I also noticed that the caps in the img below are getting hot,I checked the current of the entire circuit it was 150mA, maybe there is a short or an IC got damaged idk, I'll continue checking
https://i.ibb.co/b19DCp7/20200228-124110.jpgComment
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Oki I removed U106 and U107, again I measured the output's at the Tl's the voltage was like 6v and the caps still getting hot, I really think the problem is with the Tl's, I'll go tomorrow to the city and buy a new ones,
Addition: I removed the two Tls (didn't put a new ones yet) and I removed the coil, then connected the device to the battery,but the hotting thing didn't gone, I found that not the caps is causing the heat,but the 100ohm resistor near them at the rail which connected to the +12 battery (as the img below shows),I can't even put my finger there it's too much hot, that is not normal right?
https://i.ibb.co/tbYWHZW/20200228-145753.pngComment
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Those Electrolytic caps are simply the Input and 8V regulator filters. No way should they be hot even if there is a short some where on the board.
Did you connect power reversed????
They Will Damage electrolytic caps.Comment
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Can you check my above comment, I added to it, and yes I connected the battery the right way I'm sure, it's the rail at 100ohm that getting too much hot,not the capsOriginally posted by waltr View Post
And do you know how much your circuit consumes current?,I put multimeter from the positive battery series to the input circuit without the coil and the current was 150mA,normal?Comment
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Waltr, I was adding a pot from TR2 collector to the ground for volume control (I saw you posted that somewhere in the forum),and when I removed it the heating problem is gone and the current becomes like 40mA with coil connected, are you sure you have a volume control connected like this way?, and tomorrow I'll buy a new ICs which I have removed and will see what would happen.Comment
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That 100 Ohm resistor is power to the Audio transistors. This audio circuit is NOT designed to be on 100% of the time so makes sense the 100 Ohm gets hot if it is constantly beeping.
Maybe the transistor is now bad. Try removing it and re-check- better to trace the signal back as follows.
Or it could be the LM358 (U107) that is bad holding the audio transistor on.
Or could be the comparators (U106) turning on U107 and then turning on the audio.
Or could be a short or other problem on the traces from U104, U105 outputs into the comparators inputs. Ensure Pins 3 & 5 are lower than the references pins 2 & 6.
Current draw with the Audio Beeping is about 150mA. With no sound the current draw should be closer to 50-60mA.Comment
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Read my last post,Originally posted by waltr View Post ,do you know other way to add volume control?, which method you use
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Originally posted by waleed View PostOriginally posted by waleed View PostRead my last post, ,do you know other way to add volume control?, which method you use
Ahh..I posted while you were posting last one.
I have never put a volume control on the TGSL. I take the TGSL audio out to a BlueTooth module - to BT headphones which have volume control. Works great without the cord.
I did make some suggestions on what to try but currently do not remember what they were.
A link or picture will help my memory.
Ok, I just found the LTspice model I did for the Volume control.
This shows that bringing the base of TR2 to ground or lower, turns Off the audio and the current through the 100 Ohm resistor drops to Zero.
No R to ground has audio out at 1Vpeak into 8 Ohm, max volume.
3k Ohm to ground drop Vpeak to about 0.4V which should reduce volume.
I would try a 20k pot.
What value Pot did you connect?
Did you Ohm the Pot connection to ensure it was connected properly and you got the correct resistance range.
Connected to Ground and Not +5?
I do have a second TGSL EDU PCB that I should build just to do testing and experimenting on.
I do not want to experiment with the full detector I use since there is a good chance to break it.Comment
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First I used 10k but the sound wasn't so loud when I turn the pot to max, so I put a 100k and it worked fine,and I connected it to the ground not to tho he -5v, I didn't know that would make the 100ohm heating, so what you suggest for volume control other wayComment
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