I enjoy a circuit-bending approach to musical projects: Use low voltages, cheap or scavenged parts, and plug things together until I get something interesting. Last month, I showed how to connect an LED to the control voltage (CV) outputs on a keyboard so the LED lights up as you play. For fun, I mounted the circuit in a Japanese monster toy. (See the video at emusician.com.)
Fig. 1. Wiring layout for MIDI Din connection and 4017 decade counter/divider chip.
It’s even easier to flash LEDs from MIDI outputs (see Figure 1). Simply connect an LED between the second and fourth holes—the pins are labeled 4 and 5—with the LED’s long leg connected to pin 4. Pin 5 is normally 5 volts. It falls to 0 volts when data goes out, allowing current to flow through the LED. (Note that not all MIDI devices provide 5 volts; Ploytec, which makes the fantastic MIDI-powered PL2 synth, has a compatibility list at ploytec.com/pl2.)
I’ve built a bunch of MIDI data detectors into Ultraman monster toys, but there was one monster I’d been saving until I could work out a worthy circuit. Satan Beetle has six metallic nipples that cried out to host a spinning sequence of LEDs.
Fig. 2. Here’s a photo of how the low-cost board with the CD4017 and NE555 with LEDs looks.
My circuit uses the popular 4017 decade counter/divider chip, which takes an incoming pulse at pin 14 and distributes it sequentially to pins 3, 2, 4, 7, 10, 1, 5, 6, 9, and 11. Connect LEDs to those pins and they’ll light up one after the other, then restart. To loop the sequence before the tenth output, disconnect pin 15 (Reset) from ground and connect it to the next pin in the series, instead. For example, I wanted six lights, so I connected pin 15 to pin 5, triggering the seventh LED. You can find the 4017 in hobbyist kits; BangGood. com sells a pack of five kits with LEDs and free shipping for $5.26 (see Figure 2). Search for “CD4017 kit.”
To power and trigger the 4017, I connected pin 4 of the MIDI circuit to pin 16 of the 4017, and pin 5 of the MIDI circuit to pin 14 of the 4017. Playing notes on my Novation Bass Station II advanced the LEDs, and moving wheels and knobs flashed through the LEDs like lightning. My other MIDI gear produced mixed results, so for a more consistent trigger source, I added the option to use a CV gate signal at pin 14. You can see the Satan Beetle sequencer in action in my video at emusician.com. What are you lighting up? Send details to DIY@batmosphere.com.
Vinyl monster toy Multiple LEDs, 3–5V
LED holders 1kΩ resistor
4017 decade counter/divider chip
1/8” (3.5mm) TS miniphone jack if using CV
5-pin MIDI jack or half a MIDI cable if using MIDI