So, recently I’ve decided I wanted to start making my own little electronics projects. I’ve got a few in mind, but the first one I wanted to do was the Optical Theremin.
I have wanted an optical theremin for quite some time (rough guess would be 5 years), but the prices on them aren’t cheap (the built kits I’ve seen go for around $100), so I figured I’d see if I could dig up schematics and make my own.
To my delight, I found the RS Optical Theremin. It generates a square wave, and the tone will vary depending on the amount of light that the photo-transistors are receiving. Most of the parts for this project will be available at Radio Shack.
I quickly breadboarded-up the schematic on the website, and thoroughly loved the sounds I was getting. However, I wasn’t planning on leaving it as is, so I made a few modifications.
First, I added a power LED and power switch. The LED was handy, so I could tell if the thing was on or not.
Second, I added a volume knob.
Third, I added a killswitch pushbutton, so I could do DJ-like tap-scratching.
Fourth, I added a 1/4″ jack so I could run this to an amp or my sound card.
Lastly, I added a combo 500k potentiometer and SPDT switch. The switch activates the Killswitch, so I can either have the unit in “Tap” mode or in full-open mode (no cutting out). The 500k pot acts as a pitch ceiling. I was really liking the super low pitch square waves I was getting with very little light, so I wanted to be able to control the range on the output pitch. I hooked up a 1Meg Ohm pot and found out the 500k was the sweet zone to get the lowest of the low square waves.
Here’s a schematic I drew up, including the parts I’ve added (click image for closer view).
Next step will be transferring this to a circuit board.
After finally getting The Mole running on the breadboard and getting the customizations that I wanted worked in to the project, I decided I needed to start mapping out how I was going to transfer this to a circuit board. The original RS Optical Theremin suggested that the project would fit on a tiny 1 3/4″x1 3/4″ board available from Radio Shack (Part #276-159), but since they did not give a layout, I had to figure this out on my own.
Since I own Microsoft Office, and since I’ve used Visio a bunch for my day job, I decided to layout the board using Visio. It took me several hours to figure out the placement of components and jumper wires, but once I had something I could use as a guide for my first soldering project, I went at it.
Since some of the parts I am using are panel mount, and need to mount the the front of the “panel”, I decided to leave some parts unsoldered, but solder in their lead wires, for attachment later. Having the leads on there would allow me to test the unit before packaging it.
I ended up soldering the board in two sections, as I was getting fatigued, and didn’t want my soldering job to look like total horse shit (well at least no more shitty than I knew it was going to look like). After completing the second half, I used some jumpers to run the leads to the unsoldered parts (the photo-transistors, the LED and Killswitch) and powered the unit on. Lo and behold, it still worked!
Next step is preparing the enclosure…
I placed my latest parts order, and promptly began working on the enclosure I purchased. It’s a Hammond 1590B, which is about the same size as a traditional guitar stompbox. I knew the board was small, so fitting that in would be easy, however, all of the jacks, sensors, switches and pots I was tossing into this made it a logistical nightmare.
I got to work in photoshop, lining up parts and seeing what would fit, how they would fit and if they would clear the edges sides and “screw holes” on the box. I would make one layout and then within an hour or two, I’d find a flaw in the placement of one of the components.
This went on for days. I eventually decided I would make a mock up, using some hardboard that I had laying around in the garage. The only problem with that is the hardboard is much thicker than the aluminum enclosure, so I wasn’t able to fasten the parts onto the board.
I then figured I would just pick-up some joiner plates (typically used in house framing). Even though they had holes in them for nails, they’re cheap enough where I could test several layout ideas, to both check if the parts all fit, and to see if they are laid out in a manner that made it easy to use the device.
I finally came to a conclusion on how I was going to lay things out, so I printed out a template on my printer, and used glue sticks (the kind kids or crafters might use) to adhere the template to the enclosure.
I then used a center punch to mark the centers of the holes so my drill bit wouldn’t wander. Using a step drill bit, I carefully began to drill the holes. The first thing I noticed was how much softer the aluminum case was compared to the steel joiner plates. I ended up over-drilling one of the holes, but luckily that was a hole that was a little tight anyway, and the mounting bolts would cover the gap.
I just had to put the thing together and see how it looked/felt, and honestly, it was awesome.
Next step is finishing the enclosure.
So there are a few things I need/want to do to get The Mole wrapped up. I need to sand the case, getting rid of the flaws in the surface. I need to prime it, paint it, apply decals and then clear coat it.
Since I have never done anything like this before (I made a couple model cars as a kid, but I’ll be honest, my paint jobs sucked), so I started checking the net for ideas on how to do this. I found a giant thread of completed DIY stompbox project pictures at http://www.diystompboxes.com, and in this thread, I found a post by a fellow that laid out his process. I thought his results were nice, so I went with it.
1) Sand the enclosure starting with 150 grit. Continue sanding with finer and finer grit. Then sand with steelwool going from coarse to fine.
I cheated a bit here. I sanded until the case was shiny, and skipped the steel wool. Basically once all the imperfections were worked out, it was good enough for me.
2) Wash box with water and dish soap.
Having worked in the paint department at a hardware store as a teenager, I knew that getting rid of the debris on the working surface was important, so I made sure to do this step.
3) A shot of primer (using Rustoleum). Let dry overnight.
This was a no-brainer. Some paints may have a tough time adhering to metal, so a metal primer makes total sense.
4) Apply spray paint (mostly have been using Rustoleum – have also tried automotive spraypaint from the automotive aisle which works good, but pricey and Testors model spraypaint). Spray once in the morning before work and once in the evening. Typically about 4 coats. Just until the box has good coverage, watching specifically for the edges.
I knew I wanted to use a silver paint with a metal fleck in it, and I knew I could find something that fit that role from Testors. I ended up getting a can of Testors “Diamond Dust” One-Coat Lacquer (1830M) from a local hobby shop.
Here’s where I should warn that I absolutely suck as spray painting shit. Rather than sticking with thin coats, I second-guessed my approach and ended up overspraying a bit (the metal fleck looked uneven, which led to overspray). So after a few coats, the bottoms of the sides of the enclosure were thicker than I wanted as the paint pooled there. I let it dry for a few days, sanded it down, and resprayed. It’s still thicker than I’d like, but much better than it was prior to the sanding.
5) Once happy with paint, let dry for 3 days before applying clearcoat.
This is the hardest step, but it’s the most important.
6) Once I’m happy with the design in Photoshop and I know it will line up with the holes, print off waterslide decal (been using Testors clear decals). I usually do this during the 3 days I’m waiting for the box to fully dry.
This was nice, as it gave me something to do while I was waiting for the paint to dry. I couldn’t find the laserjet version of the Testors decal paper at the local hobby shop (only the inkjet version), but I found another place locally (a model train store) that carried laserjet decal paper under a different brand name (Experts-Choice).
The paper wasn’t cheap ($6.95 plus tax for three 8 1/2″x 11″ sheets), so I was definitely in “measure twice, cut once” mode. I must have printed 10-20 test prints on regular paper to make sure everything was perfect, but I finally decided on a finished decal design for the enclosure.
7) Clearcoat decal paper with 3-4 coats.
I knew I was going to be able to skip this step. The inkjet decal paper needs this clearcoat to ensure that the ink doesn’t run. The laser decal paper doesn’t have the same issues, however I did read that you can clearcoat the laser paper, if you want, to give the decal a little more rigidity when applying it, but like I said, I skipped this.
8 ) Apply decal. Once dry, apply decal softener. Then once dry again, cut out holes and give it some more decal softener around the holes.
Since I had never done this before, and since I had printed out an entire sheet with copies of The Mole graphics to allow for errors (there was enough space for four copies of the decals), I decided to do a test run on one of the extra joiner plates. I followed the instructions on the decal paper packaging to apply the decal, and to my surprise, it went on like butter. The key is being gentle, as the decal it very delicate once you’ve got it in the water.
Without wasting time, I worked on getting the decals applied to the enclosure. This wasn’t as easy. The front face went on without a hitch, however the back panel (power, on/off, out) got wrinkled in on itself, and after working with it for a minute or two, failing to unfold it, I gave up and grabbed one of the extras that I printed. In hindsight, those duplicates I printed were well worth it. I was able to get the backplate on on my second try.
I let it dry and cut out the holes. I then brushed on the decal softener, and much like waiting for paint to dry, this was tough waiting for. Once the softener goes on, you can’t touch the box, at all. If you do, you risk damaging the decal beyond repair, and would have to sand the case down and start back at the paint steps. I made sure to wait 24 hours before handling the box, and the waiting paid off, as the decal looked sharp!
9) Clearcoat box. Typically 6 coats. Wet sand (under a running tap) with 2000 grit automotive sandpaper after the first 3 coats. Nothing the final 3 coats.
I did at least 6 coats, maybe more, but I was fighting a dust problem. I’d spray it (using Testors high-gloss clear coat), and while it was drying, a piece of dirt or dust would inevitably end up on the face of the box. So I’d sand, and respray, over an over. It finally got to a point where none of the flecks on the surface were noticeable enough for me to OCD over. The clear coat process was the slowest taking at least a week, as the Testors high-gloss was agonizingly slow drying.
10) After it’s dry (typically leave it overnight), grab my “Mother’s Carwax” and wax and buff the box.
I skipped this. In hindsight, I probably shouldn’t have, but I guess you live and learn.
11) Grab a drink and enjoy!
This was the easiest step, and I certainly didn’t skip it.
I made a big mistake by switching out a part so close to finish. While on a regular trip to Ax-Man, I found a momentary switch that was bigger and sturdier than the tiny one I had purchased from allelectronics.com. I bought it and instantly worked it into the project. However, I neglected to move it over enough from the side of the enclosure, so in order to fasten it to the face, I had to spin the switch, leaving the bolt on the backside butted up against the side of the enclosure. Luckily this worked out for me. An additional error was made with regards to this switch, as I failed to move the label for the switch on the decal, so with the bigger hole, most of the “KILL” label is obscured. So, if you’re going to add something late in the game, make sure you measure EVERYTHING it will effect, or else you’ll end up kicking yourself. I got lucky, and things worked out, but next time I might not be so lucky.
Additionally, I wish I would have let this dry for a lot longer before assembling. If I use similar paint in the future, I’ll probably let it dry for a week or two before assembling. Right now I’ve already put a couple dings in the paint since it was so soft/not completely cured. Again, live and learn!
And here’s a video of The Mole in action: