Mousebot from Make vol 2 is a fun introduction to robotics. So fun that I've created this expanded documentation of a Mousey build from start to finish, with a few extra little tips you won't find in the mag. This how-to is best understood after reading the original article from page 100 of Make vol 2 however it is probably not required.

Mousebot is a simple bot that uses two "eyes" to sense light and then turns towards the light. A single large "whisker" is mounted on the front of the mouse to detect collisions. A collision with a wall will cause the mouse to reverse and turn then take off in another direction. This project is pretty cheap, if you have a mouse to use the other parts can be obtained for less than ten dollars.

If you have any questions or comments you can get me at jacob@makezine.com

Step 1: Gather Materials and Tools

MATERIALS
1 Ball Mouse
2 Small DC Motors
1 Toggle Switch
1 DPDT 5v Relay (Aromat DS2YE-S-DC5V works)
1 LM386 op-amp
1 2N3904 or PN2222 NPN Transistor
1 LED (any color)
1 1K Resistor
1 10K Resistor
1 100uF Electrolytic Capacitor
1 Audio Cassette Tape (you know, from the 80s...)
1 CD-ROM or Floppy Disk (for the bumper)
1 9V Battery Snap
1 9V Battery
2 or 3 Wide Rubber Bands
22 or 24 Gauge Wire (some stranded and some solid core)

TOOLS
Multimeter
Phillips screwdriver
Dremel
Small pliers
Wire cutter/stripper
Razor knife
Soldering iron
Desoldering tool of choice
Superglue or epoxy
Hot glue gun and glue
Hacksaw

Step 2: Scavenge Some Parts

The Mousebot requires several parts which we can conveniently borrow from the donor mouse, its eyes and its whisker.

Open up the mouse and locate the components that we'll be harvesting, the momentary switch and the infrared emitters (the clear ones).

Remove the PCB and desolder the push switch and both IR emitters.

Step 3: Prepare the Case

Next we need to give Mousebots insides a cozy place to reside, so break out the Dremel and remove all of the internal plastic structure from the top and bottom of the mouse. If your mouse is small you may have to remove the screw posts that hold the mouse together.

Now use the Dremel to cut openings for the bump switch in the front of the mouse and motors on the sides.

The best Dremel bit to use for this is the short cylindrical type, it will cut a good right angle if the Dremel is held vertically.

Step 4: Make the Wheels

The axles on these motors are pretty small and if we want Mousebot to be stable at blazing high speeds we need to make him some rims. Cassette tapes have a rim of perfect size in the bottom right and left corners (if the open side is down). It might take a couple tries opening different brands of tapes before you get ones that fit your axles perfectly. Once you find some rims you are happy with super glue them to the axles.

Cut the rubber band and superglue it to the rim then wrap it around three times, adding superglue every half turn or so to keep it together. Cut off the leftover rubber.

Now glue another rubber band back to the one that you just wrapped. Complete one revolution and cut off the extra. Make sure to add enough glue to keep the outside rubber band on. Repeat the same process for the other wheel

Step 5: Layout the Design and Install the Relay

There are quite a few good component layouts for the mousebot. The best layout is probably the one picture on the top of page 100 of vol 2. However this alternate setup pictured below works better on certain mice. I chose to use the standard layout. The circuitry of the mouse will be free formed since there is not much extra room for a pc board.

Once we know where everything will go its time to get to the real work. Set down the relay and solder wires in an X connecting pins 8 to 11 and 6 to 9. (see pin labels on second image)

Then connect pins 1 and 8 with a wire along the side and add stranded wire to leads 8 and 9.

Solder the collector of the transistor (right pin looking at the flat side) to pin 16 and clip the lead short. Then connect the wire we soldered to pin 9 to the emitter (left pin looking at the flat side) leaving a little bit of slack.

Now glue the relay into the case. I have added two clipped leads to act as positive and negative voltage rails which will get rid of some clutter in the motor area. Use your razor knife to strip the shielding from the wire connecting pin 9 and the emitter and solder it to the - voltage rail. Then connect pin 8 to the + voltage rail.

Step 6: Install the Bump Switch

Now lets give the Mousebot his whisker. Make it by soldering the positive lead of the capacitor and the 10k resistor to the end pin that is normally open. You can check which side is the open side of the push switch by using the continuity check feature of your multimeter. There should be no connection between the middle and normally open pin until the switch is pressed. Once this is done add stranded wire to the ground lead of the capacitor and the middle pin of the switch.

Connect the resistor on the switch to the base (middle pin) of the transistor and the wire from the ground side of the capacitor to the - voltage rail. Then connect the middle pin to the + voltage rail. To make your joints a bit more secure you can use heat shrink tubing to insulate the connections and bend the capacitor to the side to free up a little bit more space.

Step 7: Build Mousebots Brain

Mousebots brain is the LM386, flip it on its back (pins up) and bend pins 1 and 8 so that they are touching and add some solder.

Now place the 386 into position and connect pin 4 to the - rail, pin 6 to the + rail and add stranded wire to pins 2, 3 and 5.

We are almost ready to connect the motors so solder some stranded wire to pins 4 and 13 of the relay. At this point your Mousebot should look something like the third picture on this page.

Step 8: Construct Mousebots Top Half

First drill three small holes at the front of the mouse for the two eyes and sensitivity boosting LED. Then drill a larger hole for your toggle switch at the back of the mouse and install the switch to form mousebots on/off tail.

To create mousebots eyestalks twist two pieces of solid core wire together and solder the IR emitter to the leads on one end. Place the LED in the middle hole and connect the + lead to the 1k resistor.

Next use the diode check feature of your multimeter to find the - leads of the IR emitters and connect them to the - lead of the LED.

Step 9: Glue Down the Components

Use hot glue or epoxy to secure the bump switch and the motors to the mouse chassis. I used a combination of superglue and hot glue to hold in the bump switch and hot glue on the motors. Make sure the angle of the motors are roughly equal and extend down enough to raise the front of the mouse slightly off of the ground.

Step 10: Finish Up Making Connections

Connect pin 13 of the relay to the left motor and pin 4 of the relay to the right motor. Now connect pin 5 of the IC (brown wire in picture) to the ground node of both motors. If you arent sure which side is + and which - on you motor connect it to a battery and observe the direction of the spin. The right motor should spin clockwise if you are looking at the wheel and the left should spin counter-clockwise.

Locate the wire coming from IC pin 2 (green) to the + lead of the left eyestalk and IC pin 3 (blue) to the + lead of the right eyestalk. Then wire the 1k resistor to the + voltage rail.

Hook up the battery by soldering the black wire on the battery cap to the negative voltage rail. Connect the red wire on the battery cap to the switch and then connect the switch back to the + voltage rail.

Replace the cover of the mouse and then cut a thin strip of your bumper material (CD) with the hacksaw. Attach the strip with epoxy or hot glue on one side so that wherever you apply pressure the button clicks. Once you have the strip attached give yourself a pat on the back, you're done.

Flip the switch and enjoy.