I like the philosophy of using general purpose, readily available components only, so I’m drawing heavily from the circuits teached by Moritz Klein in his YT channel. This VCO is built around a CD40106 chip and a pair of BC558/548 as linear-to-exponential CV converter. I’ve put together a lot more extra features, like a Sync input and trimpots to adjust the range and centering of the Fine Tune knob (inspired by LMNC). But of course the most prominent addition is the tuner, another LMNC idea I stole. I never got around to learning Arduino, but I have experience with programming PIC and AVR microcontrollers in pure C with the help from the datasheet, and I wanted to challenge myself to come up with a simple tuner design of my own. Main difference is that I wanted to use 5 LEDs to display the note accuracy, and a separate LED to signal sharp (#) notes. I also have a switch to turn the tuner off in case I don’t want to be bothered by the flickering lights. Unfortunately I learned the internal RC oscillator of the microcontroller I used (ATtiny4313) is of course not extremely precise, so there will always be a tiny offset if I compare the central frequency with the one measured by a tuner in Ableton, for example. I have ideas to make it better, but I’ll focus on something else for now.
Here’s a demo. The LFO signal on VCO #2 comes from a Behringer Neutron offscreen.
just came back to this after having some time to take a look at the files. What’s the process for programming the attiny chip it uses?
I programmed some attiny chips in the past and it was an absolute nightmare for me, I ended up programming a bunch more than I needed because I never thought i’d get the set up correct again.
If you clone my VCO repo to your PC, the AVRDUDE is already included in folder DMH_VCO_40106_Firmware, along with some batch scripts. If the USB driver installation with Zadig went well, all you need to do is:
plug the USBasp to an USB port
plug the other end on the small 6 pin connector on the VCO
If the AVRDUDE did not return errors, just unplug everything and the VCO is ready to be calibrated.
There is the possibility that the tuner will not be very accurate out of the box, since the ATtiny’s internal RC oscillator is not perfectly calibrated to produce a 8MHz clock at 5V. I’ll post here later how to compensate for that.
And be sure to align the red strip of the flat cable with the triangle mark on the VCO, otherwise the 5V/GND will be reversed. It won’t fry anything the VCO thanks to the protective diodes, but it won’t work either.
ahh, i totally overlooked that header on the actual module. nice!
Looking at the schem and the layout again with that in mind, it looks like the header is just going straight to the pins on the IC, so could I prog it with the IC in a bit of breadboard? I wanna make sure I can successfully program the IC before I build the module.
As soon as the programming is finished (you’ll see a “progress bar” on the terminal window when you run the .bat script), the chip is reset and immediately starts functioning, so you’ll see the 6 LEDs light up in a quick succession and then go out. This is what the tuner does as soon as you power the module as a way to tell the user “I’ve been powered and I’m ready!”
The 5V and GND are provided by the USBasp itself, by the way. It will draw power from your USB port.
