Archive for the electronics Category

Oddball Hotplate

Posted in electronics on January 22, 2011 by raphaelabrams

I made a special hotplate for soldering all the circuit boards for the Blueman project. It’s 22″ long and 1″ wide. I made it out of a single block of aluminum that I CNC milled to fit two 750 watt heaters and a thermocouple. There’s also a PIC that monitors the thermocouple and has a relay to turn the heaters on and off. The display shows target and current temperatures to within 1/4 degree Celcius. Having this to do my soldering kept me from losing my sanity. There’s 0ver 1000 solder joints on each wand!

 

Shocker Swords!

Posted in Danger Danger High Voltage, electronics, Homeland Security, toys on January 18, 2011 by raphaelabrams

Yes! 800 volts of pure stupid! And they paid me!!!

I used a circuit from an electric flyswatter with the addition of a bleeder resistor on the output. It’s a very simple boost converter with a transformer on it. There’s two primary windings, so the circuit gets feedback. It’s amazing what you can get in Chinatown for five dollars! The full length of the blade has metal foil tape on it, with a channel going down the middle for sparks. The tape is coupled very crudely to the circuit because at that voltage it just sparks anyway. Hit any soft part of a person and they get a nice painful zap! Probably not dangerous? Heh! Heh!

Following will be a load of interesting things not in chronological order.

Posted in electronics, Soft Circuits on January 18, 2011 by raphaelabrams

I have been doing all sorts of fun stuff, but being very lazy about documenting it. Here goes!

Let’s start with a Soft Circuits class that I taught with Catarina a little while ago. We were doing the “voodoo doll” design, where a circuit is activated by having a pin stabbed through it. First is a happy Alexis with what might be a monkey robot. It got stabbed.

There was also a really cute little pillow guy most remarkable for having two eyes.

And finally another cyclops, but this time a bunny!

The trick to getting this circuit to work is to use conductive spandex. Yes, it exists and lessemf.com has it (catalog #A321). It’s expensive, but a little goes along way. The idea is that normal conductive fabric will not heal from a puncture — its metal fibers stay bent. But somehow this stuff springs back, making a good contact with the needle. So to make a needle activated switch you only need two layers of this stuff with a bit of felt separating them.

 

Boards are in!

Posted in arduino, electronics on May 27, 2010 by raphaelabrams

We got our custom circuit boards! You’ll probably want to change them around for your own purposes but here and here are the EAGLE CAD files. What we have is essentially an Arduino with a whole mess of servo headers and a couple of analog filters. The servo headers have unregulated battery voltage and the rest of the circuit is on a 5V regulator. The filters are envelope followers with a buffer stage to feed the A/D inputs on the AVR.

Here it is with parts soldered in:

Japanese readers: Just be glad I’m practicing my calligraphy, OK?

Good Bends and Bad Bends

Posted in electronics, Hot glue is the best thing in the universe. Deal with it. on May 26, 2010 by raphaelabrams

Free-form or “dead bug” construction can be great in a pinch. It’s a little tricky to get it right, though. One thing to consider is proper bending. If you completely flatten the pins on a DIP package it will look nice and neat, but the bend will happen at a place that was bent before. It’s going to break. Look at the arrow, you can see a tiny bit of metal peeking out of the chip where a pin broke off.

Now if you only bend up to the shoulder of the pin you’ll be bending fresh metal. It won’t break as easily and is nice and springy.

Of course fragility and breaking are a major part of free-form circuits. There’s no way to make anything really strong with this technique, so if there’s time make real circuit boards.

Oh, and when you’re done cover it in hot glue.  Just go crazy. This actually does a pretty good job of keeping everything together, and is mostly waterproof too!