Tiny Bot

This has probably been done to death on the blogs but I was inspired by the born 2 craft site. Mine needs a bit of work in the code but I generally prefer to do something from scratch by myself after seeing an idea. Mine is also a bit larger as it is veroboard.

Design

The parts are all hacked off of other dead RC toys and boards, ATTiny85 is the only thing I paid for, makes me happy. The system uses a small LiPo striped from crashed mini RC helicopter, nice and light. The board layout was worked out in building, working around the socket as it was meant to be a 8 pin PIC proto-board. 

The wheels were made from ABS sheet, using a circle template at 23mm. Using the four centre marks on the diameter I drew between opposite ones to get the point to make a hole for the shaft, I used a dividers point and checked every now and then to see the fit, just push on with reasonable pressure. 
I used marine silicon to create a tread. This is done by running two strips along ABS sheet at the distance of the wheels, and roll back and forth.

The battery is charged by a full spec LiPo balance charger through the headers, the switch is moved towards the header toput in charge mode.

Some build pics, some:

Underside

Front View

Hardware

The design of the circuit is similar to the born 2 craft, but I made some modifications.

I added the flyback diodes to the two motors, I skimped on those to begin with as there was not enough space, but after changing the transistors for both motors I added them. The PCB layout is my design.

• Transistors are BC817-40
• Diodes are 1N4148
• ATtiny85/45
• Small model motors
• 0805 resistors
• LiPo 3.7v
• Switch SPST
• Wheels: ABS, 23mm dia.
• Some copper wire, varying thickness

Schematic

PCB

Code

/*
Tiny Bot: an LDR based light following robot, or avoidance bot
 if you switch the drive function around.
 Hardware is based off the Light Bot by born 2 craft

 TODO:
 Add IR control
 Clean up code
 ##############################
 Written by:
 Reece May 
 rev1 12/15/14
 https://ziggyelectronics.blogspot.com

You may use the code and modify it as long as you keep the above
and make edit notes bellow and put it on github here:
https://github.com/ReeceM/Tiny-Bot.git
 */

#define Rmtr 1
#define Lmtr 0
#define Rsens 3
#define Lsens 2
#define drive_time 100

int Rav, Lav = 0;

void setup(){

  pinMode(Rmtr, OUTPUT); 
  pinMode(Lmtr, OUTPUT);
  pinMode(Rsens, INPUT);
  pinMode(Lsens, INPUT);

}

void ADread(){
  Rav, Lav = 0;   //clear the average to prevent errors

  for(int q = 0; q < 20; q++){ //loop to create average

    Rav += analogRead(Rsens);
    Lav += analogRead(Lsens);
  }

  Rav /= 19;
  Lav /= 19;
}

void drive_RIGHT(){
  digitalWrite(Lmtr, 0);

  digitalWrite(Rmtr, 1);
  delay(drive_time);
  digitalWrite(Rmtr, 0);
  delay(drive_time);
}

void drive_LEFT(){
  digitalWrite(Rmtr, 0);

  digitalWrite(Lmtr, 1);
  delay(drive_time);
  digitalWrite(Lmtr, 0);
  delay(drive_time);
}

void loop(){

  ADread();
  if(Rav < Lav){
    drive_RIGHT();
    //drive_LEFT();  //use this to avoid light
  }
  ADread();
  if(Lav < Rav){
    drive_LEFT();
    //drive_RIGHT();  //use this to avoid light
  }
}

Links
https://github.com/ReeceM/Tiny-Bot.git