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Topic: simple circuit reverse engineering (Read 1 time) previous topic - next topic

cloxart

Hello everybody,
I do have a temperature sensor that i am trying to integrate in a project. The device was supposed to be an infrared temperature sensor, but when i opened it up to try to understand how to get a useful signal out of it I only found a small PCB with a LASER diode (TOSHIBA TOLD 9200) pointing at the lens. I understand that the laser beam is used as an aid in aiming the sensor at the correct spot for temperature reading, and since there are no other components pointing at the lens, I can only guess that the tiny signal from the photodiode inside the laser diode is used to get a reading (obviously after turning the laser off). this is supported by the presence of an OP AMP (AD760). I have drawn up the circuit board and I am attaching pictures of the original board and my drawings (one of them with transparent components so you can see where the tracks are going underneath them). I have ZERO experience with SMD components, I managed to understand that the black ones (marked 1002) should be resistors and the glass orange one a diode. the other components (gray ones) are they capacitors?? there are no marks on them. and the black one with three pins marked A7p what is it?? (only 2 pins of it are connected) I tried to search the net but had no luck. there are 5 wires coming out of the device: yellow, white/red, green, red, black.
Is there anyone who can help me make sense of that? (I am ready to pay for that if needed)

Kind regards

PaulRB


jremington

You have not explained what you actually want to do, but to attempt to reverse engineer a device like that, as a novice, is not a good way to start any project.

If you want to use an Arduino compatible infrared, non contact temperature sensor, I suggest to get the MLX90614 individual sensor, or the Grid Eye 8x8 thermal camera.

If you carefully follow just about any of the many tutorials on line, they will work right away.

cloxart

Hello jremington,
thanks for your reply. What I am doing is an automatinc welding machine. In order to know when to start the welding process I need to know when the part reaches the set temperature. The reason I need to use that particular sensor is that I have 5 of them available, taken from old welding machines and doing that exact job of sensing the welding temperature. I am by no means a "novice" with arduino and programming, but i can only define myself an "hobbyist" regarding electronic, and I never ever used SMD components, that is why I am asking for help.

jremington

You are definitely a novice with reverse engineering.

Good luck with your project!

cloxart

Thank you again jremington for your post,
but if all you have to say are derogatory comments I would suggest that you dont waste your time on that.

Regards

jremington

There is nothing "derogatory" about being a novice. Everyone has to start somewhere!

cloxart

I still think your comments are not adding anything to this forum, and not offering any help..., just wasting space and time.

Paul_KD7HB

Get a box of colored pencils.

With a regular lead pencil, draw a box on a sheet of paper for each and every component on the board. Label the boxes with the id of each component it represents.

Pick one box and with a colored pencil draw all the connections from that component to every other component. Lay that color aside.

Pick another color and begin to draw the connections for another box.

When all done, draw a proper schematic using standard symbols. All connections needed for the schematic should be apparent from your colored pencil drawing. Where multiple colored lines connect components, you know only a single board trace connects them all.

Paul

cloxart

Thank you Paul,
that is what i did to obtain the drawings I posted... but i still do not know if the gray/brown parts are capacitors or what... and what A7p is, I was hoping for some help in identifying those parts.

Paul_KD7HB

Thank you Paul,
that is what i did to obtain the drawings I posted... but i still do not know if the gray/brown parts are capacitors or what... and what A7p is, I was hoping for some help in identifying those parts.
Did you try your ohmmeter?

Paul

cloxart

yes
Did you try your ohmmeter?

Paul
Yes, and the black ones looks indeed resistors (marked 1002 and reading indeed 10Kohms) the gray parts all read as no conduction but one, which reads 22Kohms so I take that's a resistor, which would make sense as it is the one connected to the non inverting input of the op amp. still struggling with the A7p... 3 pins so at first look i thought it was a transistor, but only TWO pins of it are connected.

cloxart

I can only make sense of the circuit if I assume that A7p is a diode. I indeed sketched up the circuit in a simulator and it is working if I apply 12V to yellow and 5V on red, GND on green and I take black as output.
in that way I can get an output on the black wire depending on the voltage (0~20mV) I apply on on the feedback pin of the laser diode. Still no clue about the red/white wire. (the original equipment is connected through a shielded cable, and the red/white is connected to the outer mesh of the cable, but NOT to ground)

ted


cloxart


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