Digitally Controlled Circuit Bending

Circuit bending doesn’t get a lot of respect around some parts of the Internet we frequent, but there is certainly an artistry to it. Case in point is the most incredible circuit bending we’ve ever seen. Yes, it’s soldering wires to seemingly random points on a PCB, but these bend points are digitally controlled, allowing a drum machine to transform between bent crunchiness and a classic 1980s drum machine with just a few presses of a touch screen controller.

All circuit bending must begin with an interesting piece of equipment and for this project, [Charles], the creator of this masterpiece of circuit bending, is using a Roland TR-626, a slightly more modern version of the TR-606, the percussive counterpart of the infamous TB-303. The circuit is bent in the classical fashion – tying signals on the PCB to ground, VCC, or other signals on the board. [Charles] then out does everyone else by connecting these wires to 384 analog switches controlled by an Arduino Mega. Also on the Arduino is a touch screen, and with a slick UI, this old drum machine can be bent digitally, no vast array of toggle switches required.

[Charles] has put up a few videos going over the construction, capabilities, and sound of this touch screen, circuit bent drum machine. It’s an amazing piece of work, and something that raises the bar for every circuit bending mod from this point on.

Thanks [oxygen_addiction] and [Kroaton] for sending this one in.

16 thoughts on “Digitally Controlled Circuit Bending

  1. “[Charles] then out does everyone else by connecting these wires to 384 analog switches controlled by an Arduino Mega.”

    Whats an ‘analog switch’ in this context? equivalent to a transistor or mosfet?

    1. Most equivalent to a MOSFET. A MOSFET is bidirectional, current can flow in either direction through it when turned on. But a lone MOSFET isn’t very good for analog bidirectional switching, because:

      1) When off, current can still flow in reverse through it, through the “body diode” (a side effect of how MOSFETs are made, that acts like a separate diode in anti-parallel).
      2) Let’s say you have a single N-channel MOSFET. To turn it on, the gate must be some volts lower than the channel voltage. So assuming you don’t want to bother with a negative power supply and can only go as low as 0V on the gate, then the minimum voltage you can switch is limited to a few volts higher. With many MOSFETs, you couldn’t switch a 2V analog signal, for example.

      Putting two MOSFETs in series, but facing in opposite directions, gives you something more useful:

      This shows the body diodes as separate components. Try imagining how current flows in either direction when both MOSFETs are on, or is blocked when both are off.

      1. They are like “Bidirectional-Transistors”.
        If a Control-Pin is high, the two Analog-Pins have a low-resistance connection.
        If a Control-Pin is low, the two Analog-Pins have a high-resistance connection.
        This works over a more-or-less big range of voltages and currents in both directions.

      2. It functions just like a physical switch. Or more specifically, like a relay.

        They all have their own characteristics forthings like On and Off resistance, maximum voltage, switching times etc.

      1. Hello, owner of a 626 and 707 here, former owner of a 606.

        TR-606 is an all-analogue design (for the voice circuits).
        TR-707 is all sampled voices (digital)
        TR-727 is a 707 with Latin percussion samples.
        TR-626 has both rock and Latin samples.

        There are a number of other differences between the machines. Calling the 626 “a slightly more modern version of the TR-606” is not particularly accurate.

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