I changed it a bit by having the 4017 outputs drive transistors that switch current to the pitch pots (instead of turning on LEDS). Also, I triggered the chips RESET on step 4 instead of using all ten steps.

The sound is generated by a toy piano that I hacked up. Each of the four steps in the sequencer is routed through a 100K pot that varies the resistance to the piano and triggers different notes. I also threw in a touch point for garbling up the sound.

Here it is in action:

The basic schematics for the APC are pretty simple:

The entire thing is built around a cheap 556 dual timer IC. GetLoFi sells a kit, but I chose to get the parts from Mouser and wire it up on perfboard.

The APC is plenty noisy on it’s own, but I wanted to get a little more out of it: I replaced R1 with a photoresistor, added a touchpoint to pin 1 of the IC, and added a simple slide switch for toggling between two 500K pots for the main pitch control. I also removed the volume pot and went straight to a line-out because I’ll be plugging this into a mixer.

The mods give this APC some more character and make it way more fun to play with:

See you next week with a nifty DIY MIDI controller.

Here’s the first entry, a simple synth I built over a weekend based on a 555 timer IC. I used this schematic as a starting point:

I added a single 500K pot as a course pitch adjustment, and a board of resistors I pulled out of a toy piano to simulate some keys. I also converted the speaker output to a line-level output with a couple more resistors:

To play it, i have two probes from an old multimeter wired in line with the potentiometer. Touching the probes to opposite ends of something resistive (in this case, the resistor board contacts from the toy piano) cause changes in pitch.

Here it is in action:

The whole kit was pretty simple to put together, and DFRobot throws in a couple of nice extras like a toggle switch for power, and a female receptacle you can use for your charging system. All in all, it seems like a pretty sweet deal at ~$50.

I’m using the platform with an Adafruit Motor Shield and an Arduino to control the four included gear motors. This probably isn’t the optimal solution, because the yellow motors that come with the platform have a stall current of 1.5 amps at 3 volts. The Motor Shield has a max current of 1.2 amps per motor. I did some testing and couldn’t get the motors to pull more than 700mA so I should be OK, but it is something to consider.

The biggest hurdle in getting the platform working with the Motor Shield was the fact that the motors would not run consistently: they would stop and start at random intervals. After half a day of research, I came across this post describing exactly the symptoms I was experiencing. My solution was to solder .1uF caps across the leads on each motor. They’ve worked without a hiccup ever since.

My other big concern was load capacity. I’ve managed to carry about two pounds with the platform, but any more weight and it just won’t move.

My original steering plan for Pedro2 also would not work here. I had initially planned to rotate the robot by spinning the left and right wheels in opposite directions, like a tank. Due to the spacing of the tires, the four wheels actually work against each other when this is done and the tires will eventually work themselves right off the gear motors (they just press on to the motor nubs). My solution was to only slow the motors down on the side that I want to turn in. The turning radius is greater (no more turning on a dime), but the tires won’t pop off and all four motors will push the robot through the turn now.

So it wasn’t quite a plug and play solution, but it does look like this will be an adequate base for Pedro2. Here’s a quick shot of the upper level chassis I’ve put together paired with the mobile platform:

It was built only with an Arduino, a servo, and miscellaneous things I had laying around. The main body of the trap is made from two plastic Tupperware type containers. When the mouse enters the lower container to scope out the cheese and breadsticks I have in there, a small tripwire signals the Arduino to activate the servo. The servo has a string attached to it, which pulls a pin and allows the weighted upper plastic container to drop, effectively sealing the little invader and allowing me to humanely deposit it outside.

The trip wire is made from a flat piece of tin and a piece of small-gauge wire. The wire hovers over the tin by a fraction of an inch, and the slightest pressure forces it down to make a connection. It’s really just a super-sensitive homemade switch.

The code is pretty simple; really not much more than an adaption of the Servo code that can be found in the Arduino examples.

Arduino Mousecatcher source

I’ve got the trap situated in the corner I’ve seen the mouse poking around… now it’s just a matter of time.