It's been nearly three years since you first funded us in the summer of 2010. Bushy-tailed and starry-eyed, Zach and I rushed into making our dream - an educational electronics company - a reality. We expected to roll out kits like hot-buns out of the oven, but quickly realized that school would take up more time than we had thought. Within four months we managed to finish two of the four kits, rolled out circuit boards, and began development of our very own tiered documentation platform. As late November hit, schoolwork took priority. Fast forward a year and Zach and I were both studying at MIT, though neither of us allocated enough time to get Olopede off the ground.
The last time you heard from us was the summer of 2011. A lot has happened since then, but we haven't kept you in the loop. We owe you an apology.
Kickstarter - we're sorry. We're sorry that we were unable to hit our optimistic goal of pushing four kits in a matter of months. We're sorry that progress has been slow over the past two years. We're sorry that we haven't stayed true to our promises of thorough communication and openness. We're sorry that we may have given you reason to lose faith in us.
But with every gloomy, sob-spewing, cloud there is a silver lining. Since graduating last year I took a bike ride from New York to Seattle, flew right back to Boston, and have worked on olopede since. I've spent the past four months concocting a mid-range performing, easy-to-understand, voltage-controlled-oscillator core for fungen. I took inspiration from a few function generators that were top-of-the-line in the 80's (the wavetek 182A is a nice one to look at), reverse engingeered the conveniently provided schematics down to their core concepts. I figured out ways to replace the non-intuitive clever solutions that expert engineers used to optimize their circuit with simpler and more intuitive designs. I built myself a prototype that has exceeded my expectations for fungen in both simplicity and functionality.
If the image above doesn't make any sense to you, have no fear! It's actually a lot simpler than it looks. Before I go on and describe it's functionality, I should warn you that there may be a bunch of technojargon below for the uninitiated. When we actually write up documentation for fungen and the rest of the kit crew, we won't take any prior knowledge for granted and we'll explain everything from scratch.
What you see above is a culmination of research, reverse-engineering, theoretical analysis, and quick hacks. The heart of the voltage controlled oscillator is the voltage-ramping capacitor driven by a diode gate. The idea is to use a capacitor as a charge bucket. Like a normal bucket, when you put water (charge) into a bucket the water level (voltage) rises. If you keep the flow of water constant, then the water level rises at a constant rate. The higher the flow, the faster the water level raises. If instead of filling the bucket you drain the bucket, then the water level will fall at a constant rate. The hard part is switching between filling and draining thousands of times a second without letting any extra drips get in (charge dump, so to speak). To switch, we use a fast pair of valves: a diode gate. The falstad simulation should help to explain how this works. When the voltage on the left hand side of the gate is higher than that of the right hand side, the capacitor is charged by the upper current source, and vice versa.
Here's a picture of our triangle-wave generator oscillating at 1 Hertz (once per second).
and at 500 Kilohertz (500 thousand times per second) ! That's a 10V peak-to-peak signal, for those interested.
The dashed lines are the driving square wave, which is actually generated by an inverting schmitt trigger that detects when the triange wave reaches +/- 5 volts and triggers the capacitor to start draining or charging, respectively.
The whole thing is voltage controlled, too, so you can sweep from down under 1Hz all the way up to 20KHz with a simple DC voltage swing. Switch in a different capacitor and you'll be able to go from 2 KHz to 2 MHz. Not so shabby for <$10 of parts.
Next to come is voltage controlled duty cycle, a voltage-controlled output amplifier stage to drive some serious loads, precision current sources, and a sine waveshaper to get some pure tones.
During my bike trip we let our .com TLD expire by accident, which was quickly picked up by an imposter who is now copying our homepage content onto their wordpress site. Don't give olopede'dot'com any attention. It isn't owned by us anymore and we're working on getting their hosting provider to respond to our DMCA takedown notices. We still own olopede.net and will continue to post updates there.
-Zach and Josh