It's been a while since I've posted my last project

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I just wanted to share a nice little project i have done recently for our company.
Nice beginner project and it might be interesting for someone who wants to use the TCRT5000L sensor.
We have a very old RA4 photo paper developing machine in our lab (from the early 80s...) . It's doing it's job fine, but the corrosive chemical vapors are not that good for the electronic boards in the back of the machine and they get heavily corroded over time.
As you can imagine, they stop working...
This time it was the infrared rotation speed sensor board which is needed to get the run speed of the machine and so adjust the replenishing rate of the chemistry (i won't go into detail...).
Here some photos of the old PCB and my new prototype board. This type of simple circuit is also sometimes used in robotics too for line detection or object detection, so it might be interesting for you.

As you can see, the traces of the old board are almost gone...
I have ordered some blue plastic spray (will arrive in the next days i hope) and will cover the new boards (there are 2 identical in the machine) completely in plastic to protect them. We will see how it works out

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The chinese 4x6cm mini PCBs i had laying around came in very handy. Not as nice as an etched PCB, but i'm very limeded in repair budget and it works.
I have done 3 new pads with some cut out metal and the original pads at the PCB edge i have removed with a hot soldering iron. Just 3 Pads are used. Even on the old circuit (there seems to be much stuff on it which is not used...i don't care

). Connections are from top down: +15V, -slit- , Ground, Signal out (0V/15V).
Here is the new board installed:
As you can see, the sensor is looking on a black plastic wheel with white stripes like this:

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This way the rotation speed is measured. The sensor puts out a rectangle wave. When he sees a white stripe, the output changes. The analysis of the signals is done in another logic circuit.
Here is the schematic of this simple circuit. You can easily make it work for lower Voltages(like 5V or so) by just changing the resistor value for the IR LED:


(I had to photoshop out all the part numbers, because they differ from my schematic... i'm not so familar with the fritzing pcb software... but this is how the layout for the 4x6cm pcb looks like.)
Yes, right angles everywhere

, it's a proto board.
It uses the TCRT5000L IR proximity sensor for detection. An LM 358 OpAmp is used as comparator and the detection level is adjusted with the 10K trimmer.
Works quite nice, it can differenciate between black and white areas. But distance is limited to under 2cm. With a bigger IR LED/phototransistor combination you can reach a higher distance, but i was happy to get at least a TCRT5000L (a combined IR LED+phototransistor sensor)...

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Have fun with this nice beginner project

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