Need help use LM358 circuit with Arduino micrcontroller ADC input

I want to implement a LED fault compensation circuit. When a LED has failed, there will be an open circuit and no current will flow through the string. Hence, a zero current will be sensed at the RS and it will be feed backed through ADC to the microcontroller. The microcontroller will take response.

but I can't get the signal at ADC, please advice my circuit any wrong.


attached hereenter image description here


1 Answer 1


R8 is connected to ground at both ends. The feedback for the opamp won't work properly. It is likely that the output of the opamp is stuck at one level

Disconnect the wire from opamp pin 2 to the bottom connection of R6.

  • \$\begingroup\$ Also, for what it's worth, Q8 is probably backwards, although without seeing the rest of the circuit I can't be positive. Also, the ADC should be seeing about 3 volts when the LED is on, since the LM358 is running open-loop. \$\endgroup\$ Sep 19, 2015 at 3:53
  • \$\begingroup\$ Yes, I was disconnected the wire between pin2 and ground, and exchange Q8 D&S. But still not receive signals at ADC IN \$\endgroup\$
    – Wei
    Sep 19, 2015 at 4:05
  • \$\begingroup\$ What do you mean by "not receive signals"? You need to tell us exactly what you see. What voltage, how it varies with LED state, ADC reading... \$\endgroup\$ Sep 19, 2015 at 16:06

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