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  • Writer's picture1/4" Jack Of All Trades

Physical Computing Week 7: Logical Next Steps

Featuring the following ICs:

SN74HC595N - 8 Bit Shift Register

SN74LS08N - AND Gate (green LED)

SN74LS86N - XOR Gate (separate red LED)

I got the shift register circuit for the labs up and running and tweaked the code a little, adding some randomness. I also had some random logic ICs lying around so wanted to test them a bit. I also started thinking about how I could use them in an audio circuit, in a simillar way to a eurorack clock divider/logic modules, which can be very powerful in progressive droning systems.

Code from lab video setup:

    int latchPin = 5;
    int clockPin = 6;
    int dataPin = 4;
    int outputEnablePin = 3;
    int randomMin = 0;
    int randomMax = 255;
    byte leds = 0;
    void setup() 
      pinMode(latchPin, OUTPUT);
      pinMode(dataPin, OUTPUT);  
      pinMode(clockPin, OUTPUT);
      pinMode(outputEnablePin, OUTPUT); 
    void loop() 
      leds = 0;
      for (int i = 0; i < 8; i++)
        bitSet(leds, random(0, 7));
      for (byte b = 255; b > 0; b--)
    void updateShiftRegister()
       digitalWrite(latchPin, LOW);
       shiftOut(dataPin, clockPin, LSBFIRST, leds);
       digitalWrite(latchPin, HIGH);
    void setBrightness(byte brightness) // 0 to 255
      analogWrite(outputEnablePin, 255-brightness);

Beyond the labs:

I carried on researching audio circuits; there is a wealth of information out there from DIY guitar pedals and eurorack modules to emulating expensive bits of classic studio hardware and sifting through it has been interesting but time consuming. I tried and failed to make a low pass filter circuit, but will be attempting it again this week.

I also bought some random Cs from interesting synth and audio DIY projects I found online... I think I've caught the bug.

Recording some organic analogue noises

I got tired of running out breadboard space, so I bought a few modular ones that easily slot together, allowing me to have tidier setups. I have also been cutting wire to make my own breadboard cables to keep things even tidier - especially for the power and ground pins of ICs that only need patching once.

I carried on messing around with different connections to get interesting audio synthesis results. I used an LED and an LDR to make my own vactrols to control parts of the circuit, while the experiment succeeded the sonic implications were not that exciting. In my research I found out that vactrols create current dependent resistance, leading to slow reaction time (source pending), but this could be desirable in a post apocalyptic drone synth.

In my circuit, it functioned mostly as a rhythmic device and I am interested to see if I can get it functioning with a complex logic network in the future, maybe using my Russian quad SPST chip to quickly switch between different oscillator voices.

I wanted to test out a series of videos involving audio with shift registers but sadly did not have enough time to make them myself.

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