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mcp23017 resets and relays stop working!

Former Member

Hello,


I have attached AC fan as load to my SainSmart 8 Channel DC 5V Relay Module.

The relay board is supplied with external power supply(5V,1Amp).The relay board is controlled by MCP23017(gpio expander ic connected to my raspberry pi).

The fan is with Regulator.Sometimes when i change speed from regulator the ic is reset and relays stop working.

Parents
  • 0

    1st image is the circuit with capacitor across vdd and vss which is succesfull in protecting the spikes ( reducing enough to not reset the mcp).

    2nd image is when i tried the mov across the load as well as across the relay contacts later. both places mov failed to protect from spikes and eventually reset.imageimage

    .

  • 0 in reply to Former Member

    Nilay

    The SCL and SDA pullup resitors need to go to the 3v3 supply as the RPi is a 3v3 device NOT 5v.

    http://www.raspberrypi.org/documentation/usage/gpio/

    http://elinux.org/RPi_Low-level_peripherals

     

    Thats the entire reason you have the MCP23017 in the circuit.

     

    Mark

  • 0 in reply to mcb1

    Well..... it is debatable weather they are required/allowed/not allowed.

     

    In practise the 3.3V signals from the raspberry pi will reliably read as "high" on all my 5V devices. So IMHO that rules out "required".

     

    With the 4k7 pullups in parallel with the 1.8k pull-to-3.3V resistors on the effect is a 1.3k pullup to 3.8V. This makes the "high" level slightly easier to detect (a bit more margin) than without the pullup, while still within 0.5V from the 3.3V of the 'pi. Going any higher will cause a current to flow through a protection diode INTO the 3.3V line of the broadcom. Those diodes are designed to withstand a short current pulse, but not a continuous current. On the other hand, they don't explode the second you use them. They are designed to protect the chip! So limiting the current to 1mA will keep the diode in one piece. So IMHO, this rules out "not allowed".

     

    Oh, and putting the pullups to the 3.3V is completely useless, as the raspberry pi already has pullup resistors on the board. So that would just lower the pullup resistor value a bit. The foundation decided 1.8k was a good value, so why change that?

     

    I personally would try the simpler circuit without those resistors.

     

    On the other hand, I sell proper level shifters if you want: I2C Level Shifter.

    Or you can get it integrated in the small breakout board that we sell to get a "neat" 4pin I2C connector: Raspberry Pi Serial BoB (this one also breaks out the SPI and UART busses).

  • 0 in reply to mcb1

    Yeah you can get away with murder with respect to the correct signal voltages and correct line termination. If that works then great then we wouldn't have this conversation. If it doesn't then it's good to reduce the potential issues by having the correct signal voltages and termination.

     

    As any one tried driving the Pi and relay boar from a regulated battery source like a battery powered USB charger.. see if stuff is getting through that way ?

Reply
  • 0 in reply to mcb1

    Yeah you can get away with murder with respect to the correct signal voltages and correct line termination. If that works then great then we wouldn't have this conversation. If it doesn't then it's good to reduce the potential issues by having the correct signal voltages and termination.

     

    As any one tried driving the Pi and relay boar from a regulated battery source like a battery powered USB charger.. see if stuff is getting through that way ?

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