PPR II


This is a really old project that I was working on at the second semester of my University but I decided to write a few words just now. It is not oriented to a specific course or any other University related topic but it was purely hobby based and probably one of my favorite back then.

The idea was to create a robot like platform that will move around in wheels, cost a fraction of what was similarly available in the market and simultaneously can be programmed easily.

As a student then, I was following the first steps into the magic world or microcontrollers and digital electronics. The only possible idea that came to me at the easily reprogrammable feature was the PIC microcontroller. It was commonly available in the local market, you can find it by free engineering samples (yes, totally free) and it was really cheap! Ok, to be honest the other alternative out there was the AVR and it was a little bit better in the value for money factor but I was without any tool for this one. So, PIC it is!


The second big decision was the movement. I happened to have a bunch of motors from old toys that I broke in order to discover how they operate but without the transmission gears were totally useless. The power of those things can be compared only to the power of small insects without the magic little plastic circles with teeth on them! On the other hand I was thinking that I could make a few of them, sell them and make a small amount of money to spend in my next project. A part that you can find easily in local stores and simultaneously powerful enough to move a robot around. Like a Servo!

The good ones are cost too much and the continuous motion are ever more expensive. But if you go with a regular servo from a cheap Chines brand and hack it then you have a powerful and cheap way to move your robot. The hack is a simple procedure. Open the servo, cut the plastic tab that hold the main gear from the continuous motion and wire the internal potentiometer to be constantly a the center position (a resistor divider is OK for that reason)


The electronics part is a simple but functional design technique. A voltage regulator for 5V output from a 9V battery input. The microcontroller together with the decupling capacitors and the 4MHz crystal plus a few buttons and an alphanumerical LCD. Yes, the one that it is compatible with the Hitachi HD44780 controller.

I put everything together using the Eagle CAD software and etch the board at my room. As I happened to learn from this activity… never etch a board in a non-good ventilating environment. Especially if it is your own room! The gases produced are really nasty and if you spill a bit of them in the floor then the mark will be there forever!


The final touch was to put everything together. A 1.5mm sheet of aluminum plate played the roll of the sazi, the two servomotors are set in place with two sided tape and tireups and the PCB board is held above the sazi with four metal spacers. The two wheels are from a model shop and cost nearly to nothing for a bag of 6.

And what the name stands for? PIC Programmable Robot in the version II

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