microcontroller driving a relay with transistor and Opto-isolator

Posted on Feb 7, 2014

Controlling a relay with stm32 micro controller. For the isolation I have used a 4N33 opto-isolator. As my relay coil needs around 250 mA, I used a mps222 transistor. I figured that the logic gets inverted when I used the gpio as the source voltage for the opto-isolator led. I just used a pull up instead and connected the other end of the led part to the gpio. Gpio is open drain, I will drain around 3mA

microcontroller driving a relay with transistor and Opto-isolator
Click here to download the full size of the above Circuit.

in the pin. I do not have the R2 resistor grounded at this moment. My problem is if in case my stm gets disconnected then my relay will be turned on - which I want to avoid. Could anyone please tell me if adding this R2 will fix the issue

Leave Comment

characters left:

Related Circuits

  • New Circuits



    Popular Circuits

    12V Fan controller with PIC18F25K20
    Ultrasonic Pest Repeller schematic
    27.125Mhz Nbfm Transmitter Circuit
    Arduino Controlled Pneumatic Servo
    Diode Radio for Low Impedance Headphones
    60watt rf radio frequency
    Capacitive Discharge Magnetic Pulser