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I am controlling an ADC with my Arduino Uno. I would like the clock of the ADC to be the same frequency of the Arduino. Is there any way that I can have a constant clock output from one of the Arduino pin ?

Thanks,

Liam

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Sounds a lot like this question – Gerben Oct 10 '15 at 18:38
up vote 1 down vote accepted

This outputs 8 MHz on pin 9:

#ifdef __AVR_ATmega2560__
  const byte CLOCKOUT = 11;  // Mega 2560
#else
  const byte CLOCKOUT = 9;   // Uno, Duemilanove, etc.
#endif

void setup ()
  {
  // set up 8 MHz timer on CLOCKOUT (OC1A)
  pinMode (CLOCKOUT, OUTPUT); 
  // set up Timer 1
  TCCR1A = bit (COM1A0);  // toggle OC1A on Compare Match
  TCCR1B = bit (WGM12) | bit (CS10);   // CTC, no prescaling
  OCR1A =  0;       // output every cycle
  }  // end of setup

void loop ()
  {
  // whatever 
  }  // end of loop

How can add a prescaler?

You change the prescaler bits. You can look at the datasheet or my cheat sheet here:

Timer 1 bits

You may not need a prescaler, depending on the frequency. Change OCR1A to some number between 0 and 65535 to slow it down.

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This is exactly what I needed . How can add a prescaler ? – Liam F-A Oct 10 '15 at 20:39
    
See amended reply. – Nick Gammon♦ Oct 10 '15 at 22:10
up vote 3 down vote

You can use one of the PWM pins on Arduino to output a PWM signal. If you want a constant clock, you need to set the duty cycle of the PWM to be 0.5, i.e. 50%.

Syntax: analogWrite(pin, value) where the parameter "value" is the duty cycle ranges from 0 (always off) to 255 (always on) since it is a 8-bit PWM generator inside Arduino.

If you need a PWM wave with duty cycle of 0.5, you need to set the "value" above to be 127, which is exactly in middle of 0 and 255:

analogWrite(clkpin, 127);
share|improve this answer
    
analogWrite only works on PWM pins, not on the analog pins. – Gerben Oct 10 '15 at 18:37
    
You are right, my fault. – Penthrite Oct 11 '15 at 6:59

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