Mousey part 1: BEAM Robot

I am building a robot out of an old track ball mouse.  Resources for this project include:

Thank you Gareth for publishing this great project, and to his predicesor Dave Hrynkiw of Solarbotics who designed the Herbie  Photovore.

I collected most of the parts I needed from Vetco and Frys in the Seattle area.  In photo 1 you can see most of the stuff laid out on my desk:

Parts and tools for Mousey the Photovore

Parts and tools for Mousey the Photovore

Wasting no time, I performed surgery on the mouse.  LOOK!  MOUSE BRAINS!

Recycled trackball mouse GUTS and electrical BRAINS!

Original mouse brain

"Click" touch sensors are red buttons on black rectangles (SW1, SW3); IR light emitters are clear/white (LD1, LD2)

Next I used my new tool, the Desoldering Pump, and my trusty old soldering iron to remove the infrared light emitters from the circuit board that I harvested from the old trackball mouse.  In the photo above, the IR emitters can be seen as white/clear diodes in the bottom two corners of the board.  They are labled LD1 and LD2, probably because they are Light Diodes.  These diodes have 3 prongs, which is odd for a diode.  I shrugged and followed directions in the book to put the black wire on the anode, and red wire on cathode, which is reverse from normal, but the explanation in the book about increasing the sensitivity of the light reception seemed plausable.  One pin was left unattached.

Then I wired up the circuit from the book, which didn’t work as expected.  I poked around with my voltmeter for an hour in the late evening, then went to bed.  This morning I discovered the Mousey web site with a CORRECTION TO THE CIRCUIT DIAGRAM from the book.  Wow!  This explains the problem!  It feels good to realize I didn’t make a mistake.  So I followed the new diagram online (and made notes in The Best of Make book) and it still isn’t quite performing properly.

Testing and Troubleshooting 

Testing the circuit with the repurposed IR emitters, without the motors hooked up.  Instead of trying to observe the motor going faster or slower in reaction to light hitting the new Mousey eyes, I decided to test the voltage that would goto the motor with a Fluke Voltmeter.    In my video that I posted to YouTube, you can see that the voltage for the left motor changes when different amounts of light are shined on the left Mousey eye, which is the harvested IR emitter.   

Test 4 at 8:00 pm

  • 4.71 V  Shadow 
  • 4.92 V  Ambient
  • 5.05 V  Flashlight 8″ away
  • 5.20 V  Flashlight 5″ away
  • 5.50 V  Flashlight 1″ away


Test 5 at 8:30 pm, shown in video

  • 4.62 V  Shadow 
  • 4.84 V  Ambient
  • 4.94 V  Flashlight 8″ away
  • 5.01 V  Flashlight 5″ away
  • 5.52 V  Flashlight 1″ away


Next Steps in Testing:

  1. Find another voltmeter in my garage somewhere and test the voltage of both motors while shining lights on both of the Mousey eyes.
  2. Select and purchase two very small 5V motors that will fit in Mousey.
  3. Test the circuit with 2 motors and flashlights on the breadboard before finally…
  4. Reconstruct the circuit inside of the Mouse plastic housing.

About Christin

I build robots as a hobby and I work with software as my career. Last year I mentored a FIRST Robotics team, Team XBot. I worked at Microsoft for 11 years in such roles as developer tech support, Developer Evangelist, and Program Manager in Visual Studio.
This entry was posted in BEAM Robot, Junk Robot, Make:, Robot and tagged , , , , . Bookmark the permalink.

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