[quote author="sparkybg"]What is the resistance between the terminals of your tip you are measuring?[/quote] It's around 8.7ohm while the handle is soldered on the board but I think if I un-solder the handle, the resistance would be this amount.
I did two tests/experiments again:
1. I desoldered the handle(its terminals) from the board and plugged in the board and measured the voltage of the pads that I solder the terminals of the handle on it and it was 320mV.
2. Again I soldered the terminals but this time in reverse direction(the green wire to GND and black to the +Heater unlike earlier that I soldered the green terminal to the +Heater and the black terminal to the GND) and everything was ok but the output unlike earlier is negative. e.g. instead of showing +1.7mV it showed -1.7mV.
4. I plugged in the circuit and measured the two lead of the handle and found out there was 334mV. ok, I applied the heat and measured the voltage just like above and the result was 335mV and it went up to 336 after around 20 second and after a minute it went up to 337. no change again!
it's interesting to me. instead of going down, it goes up!
[quote author="sparkybg"]From what you measured, the op-amp behaves exactly how it should. The input at the + of the opamp should be millivolts if thermocouple is attached there.[/quote] Hi sparkybg Thanks for reply I have a question Why these thermocouples don't have any "Cold-Junction Compensation"? I think the problem is that my circuit doesn't have any cold junction.
Hi fellas About a year ago, I started to make a soldering iron based on Sparky's classic soldering iron. but unfortunately after about 3 month, I gave it up because I got busy. now I just started it again. I did everything and everything is working very well save one part. thermocouple and Op-Amp! I just have problem with this part. this is a picture of my board:
This picture shows the +input of Op-Amp:
This picture shows the -input of Op-Amp:
And this picture shows the output of Op-Amp:
The problem is that the output of thermocouple isn't correct. e.g. I measured +&-input and output of the Op-Amp and those green and black wires that are the output of the handpiece's cable and are +&- of the thermocouple. I measured all of these due to GND and the result was this:
Green wire: 0.333v black wire : 0v the +input of the Op-Amp: 0.275v the -input of the Op-Amp: 0.011v the output of the Op-Amp: 3.2v
The supply is 3.3v. as you can see the result isn't correct. What's the problem in your opinion? please feel free to ask any question. Another question, How can I find the problem? I just have a VC9805 Digital Multimeter. I really stock. I attached the schematic+two layers of the PCB.
[quote author="sparkybg"]It is 1,2,5,6 on T210 and 1,2,5 on T245. Connector 6 is for identification. There is direct connection with connector 5 on T210 and resistor on microtweezers there: [/quote]
What's the point about that resistor? I think my soldering hand piece doesn't have any resistor:
I think that yellow component is a capacitor. am I right?
Thank you so much dear equalizor for your favor :) If I were in UK, probably I would purchase two of them but there are two points that I prefer to do this myself:
1- I'm a boy from middle east (and you said if I'm from UK while I'm not)(wink) 2- and I always enjoy of doing all electronic stuffs myself!
I'm not an EE or computer technician. I'm an agricultural engineer. I know that's funny or interesting to you guys but that's what I am. :)
Ok, then I'm going to make my PCB. [quote author="sparkybg"] As I already wrote - between gate and source of the MOSFET.[/quote] Alright, then this should be ok:
[quote author="sparkybg"]Check your connections to the tip. The schematic is OK.[/quote] Thanks for reply. Could it be because of R14 (in your circuit)? because you have used a 390k resistor but I'm using a 1Mohm and also when I apply heat to the tip, it goes up. for example from -7 to -2 and when it get cool, it goes down for example from -2 to -7.
@equalizor You are right but not completely because sometimes we want to ask some questions around the T12 tips and we cannot find any guy like sparkybg that has good experience with these stuffs. :) anyway, Ok, I'm going to ask questions about and around his/her circuit.
Hi sparkybg, I found the problem. I tested the Op-Amp and found out that it has gotten hurt. eer! now, if I connect it to 3v3, it shows me 3v3 and when I connect it to GND it shows 13mv. then please ignore above circuit. My circuit is this:
That I think it's completely like this (isn't it?):
But I have a problem again :). the output doesn't give me any amount. I measured the input of the circuit and it was exactly the amount that I expected to get but it's negative. :( why? I changed +HEATER to -HEATER and it got worse( much more negative than earlier).
No, currently I'm controlling it manually. I mean I connect +HEATER to rectified 24VAC and when it getting hot I disconnect it. several images of the circuit that I wired up:
I have changed the supply to this transformed supply (because I thought the problem is my switching supply) but I still have problem with the amplifier. when I connect the input to GND, at output I have 0.3mv and when I connect the input to 3.3v(Vcc) I have an oscilated output between 20-18mv. :(
Hi sparkybg How much is the max input voltage of T-12 tips? I'm using a 24V transformer and I want to use 24VAC to turn T12 tips on but it has a 24*1.414V= 34V peak value (1.414 is RMS). I'm worry if 34v peak value would harm it.
