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DC motor control with Arduino and relay shield- coding question

• Trying to run a DC motor with an Arduino UNO and a relay shield - need help with the code! I'm using a relay shield (this one: http://tinyurl.com/pv23nve) on top of my Arduino Uno to run a DC motor for a specific amount of time after a button press. After that time, the motor should shut off. This is the code I've come up with after much struggling, but it still doesn't work (just turns on the motor for the 'long offDelay' value, then turns off, after which the button just turns the motor on for as long as it's pressed): byte relayPin = 7; //D7 -> RELAY2 volatile long lastSwitchtime = 0; long offDelay = 5000; //change this to increase/decrease delay void setup(){ attachInterrupt(1, active, CHANGE); pinMode(relayPin, OUTPUT); lastSwitchtime = millis(); } void loop(){ if ((millis() - lastSwitchtime) > offDelay) { digitalWrite(relayPin,LOW); } else { digitalWrite(relayPin,HIGH); } } void active() { lastSwitchtime = millis(); } any suggestions?

• Answer:

  I don't work with Arduino and I'm sure it probably has a safeguard about code like this (especially with timer interrupts) but I get really nervous when the main loop is running flat-out as fast as possible and possibly not letting other things get updated. I know the example code you're basing your work from does this. What happens if you skip reading the millisecond timer and do something like this instead?byte relayPin = 7;long motor_run;void setup() { attachInterrupt(1, active, CHANGE); pinMode(relayPin, OUTPUT); digitalWrite(relayPin,LOW); // start with output OFF. motor_run = 0; // start with time bucket empty}void loop() { if (motor_run > 0) { digitalWrite(relayPin,HIGH); // turn relay ON, motor runs. motor_run--; // drain the bucket } else { digitalWrite(relayPin,LOW); // no more time left, it's off } sleep(1); // come back in 1 mSec}void active() { motor_run = 5000; // mSec to run the motor}The idea here is to fill a "bucket" with milliseconds to count down. If the bucket has milliseconds in it, the output is switched on. Pressing the button refills the bucket. The sleep(1) does the work of watching the clock and coming back when it's time to loop.