Currently, I have the input of the Opto-isolator fed via a 4k7 resistor (1W). No idea how I came up with that value, but I used it before and it seemed to work.
But.... I have my doubts it's in any way correct.
The input can vary from 5v (usual) to 24v DC. It has always seemed to cope, but I would like to actually know how to work this stuff out.
The output feeds the UNO directly with a 10K pull-down.
Because you don't know basic electronics ? (like Ohm's Law for voltage, Ohm's Law for Power, led specs, etc etc etc)
If V(Rcl) = 22.75V
and I(Rcl) = 5mA (0.005A
the P(Rcl) = I * V = 0.005A * 22.75V = 0.11375W (just over 1/10th W so clearly you don't
need a 1W resistor.
8x Opto isolators all connected up. Somehow, a strip of 4R7 0805 resistors got in my 4k7 0805 resistors stock (I keep them in a clear pocket folder).
One of the resistors leading to the Opto-isolator therefore occidentally was the wrong value (thank God only one).... 5v test voltage resulted in a nice light smoke event.
Once accidently shorted an LM555 output pin (3) to the GND pin (4) while probing with a meter.
Would not have been a big deal (since it was breadboarded) but for the fact that I used a 10A
12V P.S. because I didn't have a smaller 12V power supply (current limited bench supply for example) and the result was the LM555 spontaneously combusted (burst into flames and
began to GLOW RED ! The power supply didn't have an on/off switch so by the time I got the
power cord unplugged the breadboard was melted where the chip was. (OOPS !)
I remember being very glad I had my magnifying glasses on for SMD work as the reverse installed 220uf launched itself vertically in a style that would have made Elon Musk happy.
Ricocheted off my glasses at Mach 2 and was never seen again.
I can beat that.
I was walking through the lab one day and a 2n3906 inside an open unit under test
WITHOUT A COVER detonated with a loud bang launching a cone size chunk of plastic at such a velocity that it bounced off two walls and landed on the other side of the lab. The transistor
had a cone size hole in the flat face. I was not in the ballistic path, fortunately.
To add to the OT discussion: you don't need dangerous chemicals to open the plastic package of chips. Shorting mains with the chip is a very fast way to get the bare die out of its package.
