(nato il 2.11.2001 - Scorpione)

or else...

My first (nearly) photovore


This page give the description of my first nearly Photovore. I say "nearly" because the photowore word means that the bot feed it with the sun, while my bot feed itself by batteries. Unfortunately I haven't found the right solar panel to feed it by sun.

Its name is CRABBY because of its way to walk. (this was my son idea :-)

It's designed using transistors because it's more easy to breadboad it.

The design is based on a flip-flop, a very old circuitry (now called bicore :) frequency controlled by photoresistors that change it's duty cycle also. Each side control the relative motor by a power stage similar to a Darlington stage. Motors are savaged by two old CDrom readers and they absorb 30mA alternatively. The eyes are two 1Mohm photoresistors (900 ohm in full light).

Unfortunately the bot must work with batteries because I haven't found solar cell to feed it.


The principle of operation is the following:

Under normal conditions Crabby walks linearly oscillating to the right and left because the motors are commanded alternatively; in this way the angle of view is wide (almost 180°). Really its direction is not perfectly linear but it forms a greatest circle according to simmetricity of the oscillation and the attrition that every motor succeeds to having with the floor. This however it is not a limitation because it allows him of to explore the environment for 360°.
When the photoresistor is struck by the light (the right photoresistor is the eye of left and viceversa) this provokes a variation of the duty-cycle imposing to a motor to turn for less time. In this way the motor that rotates for more time will provoke the change of direction toward her bright source.

When the two fhotoresistors have lined up toward the bright source, this will provoke the doubling of the frequency of oscillation. Crabby will be directed in this way toward the light with small oscillation right-left and to great speed, very impatient to reach it.
Obviously not being perfectly the symmetrical circuit, the collision with the bright source will not have always ; in this case Crabby will restart his search oscillating with more slow and ample movements as exposed to the beginning of this description.