7 Replies Latest reply on Nov 23, 2016 6:15 AM by user_342122993

    GPIO High On Powerup

    ben.s.

      Hello,

         

      In one of my projects, I am using GPIO pins to drive a ULN2003 Darlington transistor array. The transistor array drives some LED lamps and two relay coils.

         

      When power is first applied to the circuit, all the lamps and the relays come on for about 100mS then go into their initial states (low for all in this case).

         

      Is there any way I can force the GPIO pins to be low even on power up? If it requires a hardware change, I am open to that because I need to do a board spin anyway.

         

      I do not know if the paragraph below is relevent, but...

         

      My digital power supply uses 3.3 volts and the analog system uses 5 volts (along with VDDIO3 and VDDIO0). The relays switch mains voltage so I do not want interment turn on. The power supply for the system uses 3 linear regulators. A 24 volt power transformer feeds a 12 volt regulator. The 12 volt power feeds the LEDs and relay coils which are switched by the ULN2003 chip. The 12 volt regulator feeds a 5 volt and 3.3 volt regulator for the logic digital and analog power supplies. There are two 6800uF capacitors on the power input to allow for delayed power off.