Lightbug in search of light
Date: Monday, November 04 @ 08:48:56 EST
After several hours of fine study and experimentation until 4am in the morning, our new bug, the lightbug said hello to the world.
As the chasis, we used the previous bug's chasis; the probug, leaving the programming buttons of probug unchanged, added two feelers at the front and a fotodiod eye. For these changes to be accomplished, the circuit layout also needed to be changed a bit.
While the changes are made, the chasis is designed to be able to accommodate both probug and lightbug. Namely, with only a program change, the same chasis can both be the lightbug and also the probug. And these two species also can live in the same program which decides which bug to come to life according to light level. If light level is high, then the bug is a probug and it executes its pregiven program. And if lightlevel is low, then the bug turns into a lightbug, chasing the brightest spot. The bug mode can be changed by pressing a button.
The robot that I saw on the net and designed and produced in universities are usually use a rotating sensor to 'look around'. We also did the same thing with my msc thesis partner setrak isikbay in bogazici university of istanbul in 1996. We used a pair of ultrasonic trancievers to detect obstacles and a stepper motor to turn the transcievers 180° around. Sure we needed some big transistors for driving, a circuitry and bigger batteries for supplying the power needed by the stepper motor.
Instead of dealling with these all, our lightbug simply has a light sensor tightly fixed to the front of its chasis by soldering. And to scan its environment, the bug simply turns in steps to left and right. Though the bug weight is too low, the turning process doesn't need much energy and also the same driving circuitry that moves the robot is being used for the turning purpose. As a result we obtain a much dynamic robug with a lower cost and worktime.
When the bug reaches the source of light, the only thing it does is to hit it again and again. When the feelers touch the light source, the bug backs up and turns to opposite direction with a 'sorry' like sound. Watching the poor creature go from room to room at home by switching roomlights is very fun :)
We must say that we worked a bit more than usual to sound a "sorry" from a pic16f84.
To sense and measure light changes, we made a simple A/D (Analog / Digital) measurement system by using a capacitor. The system works by measuring capacitor charge-discharge times and is accurate enough to be used in this kind of projects that don't need much accuracy.
Though the chasis length is short and the batteries are located close to the front, our bug often tried to have front somersaults. To avoid this, a weight is soldered at the back of the bug.
As usual, the bugs circuit schematic and also the assemby source code will be added to the end of the article very soon.
Circuit schematic is added:
Click here to download
asm source code is added.
Click here to download