digitalWite problem

Using Arduino Programming Questions
#1

Please explain why this part of my sketch only works on pin 6 when run. I was expecting it to work on all. They all have been activated output prior to this code

  digitalWrite(6, HIGH);    // Turns ON Relay 3  on digital pin 6 (blue) 
  digitalWrite(7, HIGH);    // Turns ON Relay 2 on digital pin 7 (yellow)
  digitalWrite(8, HIGH);    // Turns ON Relay 1 on digital pin 8  (red)   
  delay(200);                //length of purge
  digitalWrite(6, LOW);     // Turns OFF Relay 3 on digital pin 6
  digitalWrite(7, LOW);     // Turns OFF Relay 2 on digital pin 7  
  digitalWrite(8, LOW);     // Turns OFF Relay 1 on digital pin 8
#2

What's attached to those pins? If there are really relays attached, they may be drawing too much current.

#3

They all have been activated output prior to this code

If that's the case then that code should work.

What is connected to the pins? Hopefully not relays directly.

Rob

#4

The pins are connected to a relay shield. If each of the pins are switch on then off in turn it works, but not switching all on then all off

#5

How is the shield powered? Maybe switching all on at once causes a spike in the power supply.

Try switching them all on but with a delay (say 500mS) between each one.

Rob

#6

the Arduino is powered via usb 5 volt. The shield is powered by a separate 9 volt supply and the relays attached to the shield by a separate 12volt supply. If there is no problem with the code I will experiment with some leds tomorrow. Thanks

#7