Physical Computing Journal

Totally forgot to post any up the stuff relating to the automated whiteboard drawer/dancing Beaker project. I was going to do that know, but got locked out of my apartment and can’t get in until tomorrow (day of commencement…great timing).

Circuit diagrams, pictures, video (maybe), and post-mortem shall appear tomorrow.

You can easily halve the number of pins being used for an H-bridge control and get some added safety using an inverter.

Usually you’ll want to avoid having both legs of the h-bridge set the same. So just run 1 line from the board to the input1 and run that line’s inverted value to input2.

So all in all for 2 motors and 1 H-bridge you only need 4 wires. 1 for turning the motor on/off or doing PWM speed control, and 1 for direction. x2 for the other motor. Not to bad.

I need to double check to see if the L293’s we have are actually L293D, because the ‘D’ variant has built in diodes to prevent back emf spikes. Meaning even cleaner circuit design.

Fun fact: The L293 pin’s 4,5,13,12 as heatsinks and ground. But the chip itself also has built in thermal protection so that excessive loads will shut it down before it fries itself

TI Datasheet for L293 (warning PDF)

L293 Information and Examples

Servos

For the whiteboard drawing project I’m going to need 2 servos. I have an old printer that I’m going to disassemble and hopefully salvage some useable servos. I need to do that quickly in case I need to go buy/order servos. Some information on the HiTec HS-311’s from class: DataSheet I’m controlling it with an Arduino Servo Library which allows such nice calls as

servo1.write(82)

#include <Servo.h>

Servo servo1;

void setup()
{
  servo1.attach(2);
  servo1.setMaximumPulse(2500);
  servo1.setMinimumPulse(600);
  
  Serial.begin(19200);
}

void loop()
{
  static int v = 0;
  
  if( Serial.available()) {
    char ch = Serial.read();
    
    switch(ch) {
      case '0'...'9':
        v = v * 10 + ch - '0';
        break;
      case 's':
        servo1.write(v);
        v = 0;
        break;
    }
  }

  Servo::refresh();
}

Invisibility Hoodie

Spent some hours in the lab wiring the hoodie up. Started by transfering all of the wiring over from the breadboard to a perfboard. Unfortunately it looks like the heat from soldering fried the two 555 timers.

I’m gonna spend time going through with the Multimeter more to see if I can find anything wrong, but so far everything looks fine, so probably my horrid soldering.

As for the hoodie, I have everything lighting up, and the LEDs moutned in a pretty nice way. However the IR output is just not enough. I need both more IR LEDs and higher output ones. Unfortunately Radioshack is $2/ea so thats a bit too expensive. I’m going to leave things the way they are now, and get some bulk higher output LEDs and take this proof-of-concept into a real device.

Schematics and Pictures to follow.