Gate Grinder

This is a module I’ve been thinking about since January. Nothing sexy, very much a utility module, but I was excited to get it together and working (pretty much) partly because it’s a more ambitious design project than any I’ve done before, and partly because it provides functionality I haven’t seen in any other DIY module.

I put it together tonight with a temporary front panel made of 1/16″ plywood, but I’m getting a permanent panel made. Plugged it in and it worked! That’s amazing whenever it happens, but happening with a new circuit designed by someone like me? Miraculous!

Quoting the README at the Github repository:

Kosmo format synth module, 10 cm wide, to generate clocks and act on triggers and gates (called “signals” generally herein).

Signals come from three sources. There is a jack for an external CV input (±12V). There is a pushbutton for manually created gates. Finally, there is an internal clock to produce a stream of square gates. The clock can be switched On or Off and to Slow or Fast rate ranges, and its Rate can be set, on the front panel. (Slow is around 0.14 Hz to 15 Hz, fast is 3.2 Hz to 320 Hz using the specified components.)

If the Resize On/Off switch is set to Off, the OR of these three signal sources is sent to the Out jack. Otherwise the rising edges are used to trigger a one-shot whose output width is controlled by the Resize Narrow/Wide switch and the Width knob, and the resulting signals are sent to Out. Output widths can vary from about a few milliseconds to about 5 seconds.

(And yes, the width can be set to longer than the time between two pulses. It then ignores any pulses that come along until the resized pulse ends.)

The signal at the Out jack also goes to an inverter whose output goes to the ~Out jack. LEDs indicate when Out and ~Out are on. The rising and falling edges of the Out signal are used to generate trigger pulses which go to the On and Off jacks respectively.

So one can invert gates, change the lengths of gates, convert gates to triggers, convert triggers to gates, make a gate clock, make a trigger clock.

Repository at https://github.com/holmesrichards/GateGrinder includes KiCad format schematic, PCB design, and panel design.

It’s working, but there are some issues:

  • The first run of boards was too long. What was I thinking? About 15 mm of unused space at the bottom. It can be cut off without affecting functionality, although you lose the Analog Output logo :frowning_face:. This has been fixed in the kicad_pcb file.
  • The output levels with the components I used are too low, about 3.9 volts — I’d intended more like 5V. I know where I went wrong. This can be fixed by changing the resistors in the output voltage dividers — though I’m thinking it’d be a good idea to replace them with trimmer pots. I haven’t made this change yet.
  • The trigger outputs fail to trigger some of my modules (they do trigger others), and I haven’t figured out yet if that’s because their amplitude is too small or their width is too short or what.
  • One very minor issue with the first run is the transistor footprint I used was the regular one and not the wide one. I like the wide footprint better generally, and specifically the BC547s I used have wide spaced leads. I got them in and soldered them without creating bridges, but I changed the footprints for any future boards.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s