Nash Reilly Aims to Build a Funky Function Generator — bFunc — by Open Hardware Summit 2020
Reilly's STM32-based bFunc is designed to teach him the platform, and USB, while producing a useful, open source device at the end.
Electronics engineer Nash Reilly has set himself a challenge: to create an open source function generator, dubbed bFunc, ahead of Open Hardware Summit 2020 this March — and to "put the 'funk' back in 'function generation.'"
"I’m calling this work 'bFunc' - short for 'breadboard function generator,' and also a shout-out to Parliament-Funkadelic," Reilly writes of his project in the initial design document. "All hardware must be open source. All hardware design will be done in KiCAD, so the whole world can see and copy it. All hardware design files (schematic, PCB layout, BOM, etc.) will be released for free on GitHub or some such similar platform.
"The final product must be a function generator. The product must generate sine, square, and triangle waveforms. More waveforms are possible, time permitting. The product must generate all waves with a minimum analog bandwidth of 1MHz. (I don’t think there’s a ton of hobbyist use above 1MHz, and much beyond 1MHz is getting into the point where it doesn’t make sense to be prototyping with a breadboard anyway.)"
Other goals for the project include ensuring it is built into a form factor suitable for breadboard use, and that it's ready for the Open Hardware Summit in March. "I really want to get this completed," Reilly explains, "and have prototypes in hand to take to OSHWA 2020, ideally so I can sell a few to recoup the cost of materials for the project."
The project itself, meanwhile, came about as a means for Reilly to learn more about USB and STMicro's STM32 platform, neither of which he has any prior experience in. The design includes the STM32F072C8T7 microcontroller connected to an Analog Devices AD9837 direct digital synthesis chip, plus supporting hardware. There are a few limitations in the design, mind: It won't offer amplitude control, Reilly confirms, nor will it offer DC offset or arbitrary waveform generation.
Since publishing the design document Reilly has begun a project journal — and since the end of January has progressed from researching the required parts to designing the schematics — "broke SCH into hierarchical components," he wrote in the February 4th entry, "never done a design this way before - we’ll see how this goes!" — and placing the parts, in just an hour a day. "The hour before I leave for my job every morning," Reilly explains, "to be precise."
Interested parties can read the design document and follow along with the project journal on Reilly's blog. More information on the Open Hardware Summit, of which Hackster is a proud sponsor, can be found on the official website.