I have designed a circuit with some resources from this website and I attached it here. I have given circuit connection in a breadboard and successfully run and control the speed of the motor. After a while, I moved on to the pad-per-hole PC prototyping PC board. I have given the same connection on that board. But there is no output from pad-per-hole PC prototyping PC board.

I checked connection thrice but there seem no flaws in connection. I have measured voltage in a circuit. It is as follows.

Input voltage for optocoupler - 1.2 V in breadbaord and 1.17V in pad-per-hole PC board. Output voltage(between c and E in phototransistor) - 0.005 V (in pad-per-hole board) Could not find what is the problem in pad-per-hole PC prototyping PC board connection. What might be the problem? enter image description here

  • \$\begingroup\$ What is a "dot board"? Is it a pad-per-hole PC prototyping PC board? If so, it may not have the holes connected in the same way (or at all) as the plastic breadboard. \$\endgroup\$ – Peter Bennett Oct 12 '17 at 19:53
  • \$\begingroup\$ Yes. It is a pad-per hole PC prototyping PC board. Sorry, I actually didn't know the correct technical name for that board. I have checked for continuity with a multimeter. There is no continuity problem. Actually, in that pad-per-hole PC board, an input voltage to the optocoupler is 0.3 or 0.4V lesser than the input needed for the optocoupler. (i.e) 1.17V or 1.18V instead of 1.2V input. \$\endgroup\$ – CNA Oct 13 '17 at 4:06

enter image description here

Figure 1. Test points for circuit debugging.

The circuit is so simple that debugging should not present a problem.

  • You have checked the voltage on the opto-LED. Double-check that the polarity is still right. Pin 1 should be positive with respect to pin 2.
  • With the LED off you should have 24 V at (1), 0 V at (2) and 24 V at (3).
  • With the LED on D1 should clamp the voltage rise at (2) to 5 V or so. The voltage at (1) should be a few hundred millivolts above that at (2). The voltage at (3) should be close to zero.

It's really just a matter of logically going through the circuit. When an unexpected voltage is found then you need to figure out the reason.

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  • \$\begingroup\$ Ok, will check and let you know! \$\endgroup\$ – CNA Oct 13 '17 at 8:04
  • \$\begingroup\$ I have tested all above points. Here are the details of value. At (1) potential difference is 24V as you said, At (2) value is 0V and 22.9V at (3). I felt two incidents that occurred while checking with my board. Accidentally I have shorted emitter and collector of the phototransistor and motor starts to run even if the Optocoupler LED is off. After that, I have measured voltage pin 1 of the optocoupler and it shows 20.3V. I was shocked. What is the problem here? Am I burnt optocoupler? Note: I connected SMPS 24V supply's ground and arduino gnd pin as common ground. \$\endgroup\$ – CNA Oct 13 '17 at 10:49
  • \$\begingroup\$ You forgot to mention whether those measurements were taken with the opto LED on or off. With the opto-isolator there is no need to connect the two circuit grounds but it shouldn't cause any problems. If you really have 22.9 V on pin 1 of the opto then your micro will be damaged. \$\endgroup\$ – Transistor Oct 13 '17 at 11:13
  • \$\begingroup\$ Currently, I could not get any output from my uno \$\endgroup\$ – CNA Oct 13 '17 at 13:09

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