The physical layout of the bot is very similar to the PiTronics Photovore. You also use a regular photovore design, but this type is more fun to watch. Mine adds reversible motors and an extra pair of touch sensors to Bolt's design. The light sensors point out perpendicular from the motors, one forward and one backwards.
The B-vore was made to show advanced behaviors. Hence the B in the name. It does this by changing how it reacts to light. Vores are usually made to do one thing, head toward light. However, this vore can change its behavior. It can be photo-anything, including neutral. It changes behavior based on obstacles in its path. If it is phototropic towards a lamp, and it runs into the lamp's base, then it become photoneutral, orbiting at a fixed distance either clockwise or counterclockwise. If it bumps into something again, it could become phototropic or photophobic.
How does this little circuit do all of this? Normally when a vore hits something, it backs away for a predetermined time. With the addition of a Nu based memory, it can keep on going backwards or forwards. Wilf Rigter summed it up very well, saying
The 1Nucore/memory will toggle states (oscillate) if the switch is held closed for longer than the time constant. When the switch opens it will remember the last state until leakage current changes the charge on the cap or until the switch closes again.
This memory is controlled by a pair of photodiodes. So when the light is brighter in one eye, the same motor will always turn. Which way that motor turns is controlled by the Nu memory, and this determines the behavior.
This circuit could be expanded on. For solar powered robots, a pair of diodes could be used to eliminate the photophobic response, similar to microcore startup diodes. Wilf also gave two very good suggestions:
...you can have the switches anywhere on the body of the robot! ... To make the behaviour even more interesting add a large (2-10M)resistor in parallel to the switch contacts so that once every 10 sec to 1 min the bot will spontaneously change direction and photoresponse.