In this post I’ll summarize a few hobby projects I’ve been working on, in no particular order
First off, check out my big post (soon to be a series of posts) on The CZ Tensor
(the images that used to be on this blog post got deleted, I’ll put them back up when I find copies of them somewhere)
Coemar Venus DMX interface
One of my first “serious” projects. My friends over at Radiant Atmospheres got their hands on a Coemar Venus Mentor (a very old and hard-to-find piece of disco lighting) and I decided to make a DMX control interface for it. It was going to be a very simple project at first but then I was told that it must be able to withstand accidental shorts from 240VAC to the data lines without destroying the antique equipment, so I needed to build an isolated section using an RBE-0505S isolating DC-DC converter and a 6N137 optocoupler.
It’s fairly simple anyway: The 0505S powers a MAX485 RS-485 transceiver which is hard-wired in receive mode. The receiver then drives the LED side of the optocoupler. The output side of the opto is a phototransistor, which is acting as a low-side switch with a 1k pullup. The fact that the opto inverts the signal is not a big deal–we just switch the inputs to the MAX485 to cancel that out.
The DIP switches set the address, and the pins on the edge connect to the main control board of the Venus. Most of the fun of this project was figuring out where and how to interface with the main thing–the control board is from the 70s and contains lots of bipolar logic voodoo that was fun to figure out (and no component labels. Boo).
Code on the ATMega328 is here: https://github.com/rfmerrill/venusdmx
World’s simplest (functioning) headphone amplifier
After I finished the Coemar DMX build, I had a few parts left over–namely, half of the perfboard and a different DC-DC converter (I bought two different ones just in case). This one is rather nice in that it takes 5V on the input side, and gives you a dual +/-9V rail on the out (isolated of course). So I decided that since my sound interface’s headphone output sounds like crap (it has some huge series capacitance that kills all of the bass) I would build this simple headphone amp. It’s so simple, it doesn’t even have a volume control!
For this project I experimented with alternate means of mounting jacks on perfboard. Since the Coemar DMX project showed me that drilling new holes in perfboard is a huge pain, I decided to try just supergluing them onto the board upside-down or sideways and then soldering wires on (dead bug style). It actually worked out quite well!