Most of the day was spent mounting and testing the rest of the solenoids. These little gems put out a nice 5 grams or so, depending on how much the spring is loaded and how much current they get hold of. They will do fine with a 100ms duty cycle.

I ganged them up on the back of the magnetone frame and used hot glue to adhere them to cable ties and to keep the cables managed. The glue also came in handy for wrangling the return spring. It was not attached to the body of the solenoid, so I had to come up with a clever way to do so - the hot glue was just the trick. I don’t know how many cycles it will last, but this stuff is pretty sticky, so I am pretty comfortable with it in the short run. A longer term solution with some sort of mechanical fixture would be better. As soon as I get hold of a laser cutter…

Last, but not least a soft rubber tip is needed to strike the chimes. Metal to metal is harsh, so I’m dulling the plunger tip with…drum roll…a little squidge of hot glue! It’s the salve of the prototyping gods…

The last little to-do, was to begin the breadboard for the circuit. I borrowed todbot’s clever idea to make a homespun Arduino Shield out of a perfboard and some pin-strips. In the end, the two will mate perfectly and the daughterboard will be easily removable for any maintenance or debugging…

Breadboard

The circuit diagram for the magnetone is pretty straightforward. The cool thing about the ULN2003A is that it has current-limiting resistors built in, so you don’t have to add those as separate components for each of the devices that you’ll be triggering. Any suggestions for improvement are welcomed!

Magnetone schematic

I’m calling my current project the “Magnetone” because it uses a bank of solenoids to play a set of chimes. The interesting part is the data source. At the Lab we all have magnetic swipe keycards for access to various areas. Now nobody knows what’s encoded on these cards because the information is not exactly easy to read without the right tech - and anyway who wants to bother with reading them? I wanted to reveal that data in an interesting way. We all carry around little “possible melodies” with us and the magnetone can manifest them physically.

The project uses the Arduino prototyping board to send a trigger to a ULN2003A darlington array. This allows the proper current to be activated to several solenoids which strike the set of chimes. The data source will be a magentic swipe card reader which sends regular ascii keystrokes via RS-232 to the Arduino.