Difficulty Level = 5 [What's this?]

Like many parents, we make hand-made costumes for our kids instead of buying cheaply-made (and expensive) costumes based on licensed characters. This year, my youngest son wanted to be a robot. My wife did a great job making the costume, but I just had to add some cool electronics to take it to the next level.

The electronics are nothing fancy — a simple Atmel ATtiny13 microcontroller that interfaces with two 74HC595 shift registers to light up LEDs randomly. The technical details are below, but in the process of building this, I was really struck by how electronics and computing are being embedded into everything. This week I was making a TODO list and one of the items was “finish source code for robot costume”.

OMG, now the costumes we make have source code.

This is a great example of how technology is becoming increasingly ubiquitous. Ten years ago, this would have been far beyond my reach. But in 2010 I can build this easily. The microcontroller cost $1.04, the shift register chips are $0.25 each, the resistors are a penny each, and the LEDs probably average $0.20 each. Definitely less than $5 for everything.

Technical Details

Here’s the schematic:

Schematic for robot costume circuit

Here is a closeup of the circuit board. There is a piece of clear acrylic protecting it. I ran out of 16 pin IC sockets, so the shift registers are in 20 pin sockets.

Circuit on front of costume. ATtiny13 microcontroller and two 74HC595 shift registers.

And finally, the simple source code that runs on the chip. I use CrossPack for AVR development. I use avrdude and a Bus Pirate to upload the code onto the ATtiny13 chip.

/*
 * ATtiny13 driving two 74HC595 shift registers
 *
 * Randomly turns on/off output pins of the shift
 * register ICs.
 * A random number of outputs are set high, then
 * a random time delay occurs.  Then the cycle
 *  repeats.
 *
 */

#include <stdlib.h>
#include <avr/io.h>
#include <util/delay.h>

#define DATA PB0
#define CLOCK PB1
#define LATCH PB2

int main(void) {
  int d;
  char n;
  char i;

  // set DATA, LATCH and CLOCK pins to OUTPUT
  DDRB |= (1 << DATA);
  DDRB |= (1 << LATCH);
  DDRB |= (1 << CLOCK);
  PORTB = 0;

  for(;;) {
    // choose number of LEDs to light up.
    // n will be between 4 and 16
    n = 4 + (random() % 13);

    for(i=0;i<16;i++) {
      // for each LED, probability of it being lit
      // is n/16
      if ((random() % 16) <= n) {
	PORTB |= (1 << DATA);  // set DATA pin high
      } else {
	PORTB &= ~(1 << DATA); // set DATA pin low
      }

      // toggle shift register clock pin
      PORTB |= (1 << CLOCK);
      _delay_ms(2);
      PORTB &= ~(1 << CLOCK);
    }

    // once we've shifted out all 16 values, toggle
    // the latch pin.
    PORTB |= (1 << LATCH);
    _delay_ms(2);
    PORTB &= ~(1 << LATCH);

    // delay random amount of time between
    // 100ms and 500ms
    d = 100 + (random() % 400);
    for(i=0;i<d;i++) {
      // _delay_ms function must be called with a
      // constant value, not a variable!
      _delay_ms(1);
    }

  }
  return 0; // not reached
}

Difficulty Level = 8 [What's this?]

I built a wireless robotics platform from a cheap R/C car, an Arduino with XBee shield, small microswitch sensors, and a Processing program running on a remote computer to control the vehicle. The vehicle is completely controlled by the code running on the remote computer which allows very rapid prototyping of the code to tell the vehicle what to do and how to react to the sensor events received from the vehicle. I’m hoping this is a good way to teach my 9-year old son about programming.

Wireless computer-controlled robotics platform built on cheap RC vehicle, Arduino microcontroller, and XBee radios

Before I get into details, here’s an overview of the features:

• All logic controlling the vehicle is performed in a Processing program running on remote computer. The Arduino program listens for commands from the remote computer.
• Bi-directional wireless communication over XBee radios with (theoretical) 1-mile range. I’ve accomplished 1/4 mile range with these radios.
• Sensor events are transmitted from the vehicle to the controlling computer. This vehicle has 3 microswitches – two on front bumper and one at the rear.
• Original circuitry of vehicle replaced with dual H-Bridge circuit to control drive motor and turn motor. Drive motor is controlled with variable speed.
• Power: Vehicle motors powered by 4 AA batteries. Arduino with XBee shield powered by 9V battery mounted at front of vehicle.
• Simple communications protocol: 2 byte commands from controller to vehicle, one byte sensor readings from vehicle to controller.

The Hardware

There’s nothing special about the configuration of the XBee radios. They are running the AT firmware (“transparent mode”) which allows them to simply exchange serial data. The Libelium XBee shield on top of the Arduino makes it easy to read/write serial data from Arduino code.

Arduino and XBee shield on top of the vehicle

Inside the vehicle is a simple circuit board with an SN754410 quadruple half-H driver to drive the motors. The drive motor and turn motor are connected. I had to rip out the original circuit board (but I saved it!).

Read more…