Build your own True Random Number Generator 2!

New Version! Many, many improvements.


  1. Kenji Rikitake
    Posted May 18, 2009 at 7:45 am | Permalink

    for my circuit and code on making a hardware RNG with Arduino.

  2. Posted February 5, 2010 at 9:59 pm | Permalink

    I’m confused by the choice of the 2N3904 transistors in RNG2. However, the Vbe breakdown voltage is 6V according to the datasheet ( Since the arduino usually runs on 5V, how are you getting your avalanche? I noticed in RNG1 that you use a MAX232 to get a 20V source. Are you really just measuring the noise of the ADC (probably a fine source of randomness)? Might a PN5134 work better for this application? I would really like to make a RNG with an arduino or pic, and I enjoyed learning through your experiences. I think the idea of recalibrating the system to account for component aging is brilliant.

  3. Posted February 7, 2010 at 3:25 pm | Permalink

    This RNG only works if a 12v power supply is plugged into the arduino. The Vin pin is connected directly to the power supply; therefore the circuit is at 12v and the 2n3904s can avalanche. You’re right that they don’t breakdown at 5v. If you look at the circuit with an oscilloscope you should see a healthy amount of fuzz at 12v, but at 5v there is nothing.

    If you successfully try transistors that avalanche at 5v, let me know! The power supply in this board is an extra expense that would be nice to eliminate.

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