Category Archives: Electronics

Fritzing Part for a generic Dual Motor Controller

I needed a part for a generic motor driver when I was working in Fritzing the other day, and I couldn’t find one so I decided to create one.

Download the part here.

This motor driver consists of the basics needed for any dual motor controller:

  • VIN
  • GND
  • Motor 1 IN (+)
  • Motor 1 IN (-)
  • Motor 2 IN (+)
  • Motor 2 IN (-)
  • VCC
  • M1A
  • M1B
  • M2A
  • M2B

For example the DFRobot DRI0002 2A Dual Motor Controller or the Robokits RKI-1004 5A Dual Motor Driver.

Download the part here.

iohannes: a robot based off the Sparkfun IOIO

I will post something more thorough next week, but I wanted to get some pictures and a video up for the robot I’ve been working on.

The robot was inspired by the Sparkfun IOIO: a great little board that allows you to merge the world of Android phones with the world of hobby electronics. The result? A relatively cheap robotics platform with a huge range of possibilities.

Code is here:

Here’s the breakdown:

Lynxmotion Tri-Track chassis with two 12V DC motors — $220.95 (I actually got this used for $175)
Robokits RKI-1004 Dual Motor Driver (up to 5A) — $16 (thanks, Robot City Workshop!)
12.0V 2200mAh NiMh battery pack — $24

SparkFun IOIO — $49.95
HC-SR04 Ultrasonic distance sensor — $13.95
HTC Evo — “free”
9.6V 1800mA NiMh battery pack — $18

Total cost: $342.85

Currently the robot has two modes: a manual control mode and an autonomous, obstacle-avoidance mode. In manual mode you simply tell the motors to go forward, backwards, left or right. In obstacle-avoidance mode the robot will move forward until an obstacle is detected, at which point it will execute an “evasive maneuver” to clear the obstacle, and continue as before.

Code is here:

Next steps: get rosjava installed and integrated with the application. This will allow for remote control of the robot, plus remote computation like image processing of camera data.

Remotely controlled pan/tilt camera unit


One of my colleagues at work works remotely, and we make good use of Skype and gchat to communicate with each other. However, when he’s calling in and talking to a big group, it can be hard for him to see everyone at once unless we constantly rotate the laptop around to focus on whoever is talking. Thus I thought it would be neat for him to able to control the movement of a webcam remotely.
I was inspired by seeing this pan/tilt bracket from Using an Arduino would make things very easy, since it has the Servo library and built-in serial communication. As for the “remotely controlled” part, I set up an apache webserver on the local machine (apache http server is actually already installed if you’re running OSX, more on that later) that would use a CGI script to send commands to the Arduino via a serial connection.

Parts List

Assembling the pan/tilt unit

Assembly was pretty straightforward, using the instructions on SparkFun’s product page.


I used balsa wood (available at hardware stores and art supply stores–that is, pretty much everywhere) and wood glue to provide a mount for the pan servo. This is probably the cheapest and most low-tech approach, but you could of course use any material you like.


For mounting the camera, I pulled the camera part from the base and then screwed this on to the top of the pan/tilt bracket. Again, this will depend on your camera. Some cameras, like the Microsoft LifeCam VX-3000 Webcam, have screw-on bases and thus make this part pretty easy.

Arduino connections

I wanted to keep things modular, so to connect the servos to the Arduino I installed 2 3-pin male headers on a PC board. I wired wires going from the servo signal pins to Arduino pins 8 and 9, and from the power pins to Arduino pins GND and +5V. I also threw in an LED in parallel with the power as an extra indicator that the board was plugged in and powered.

Arduino Code

githubblack Code available at Github here:

Once you’ve uploaded the following code to your Arduino, you should be able to control the pan/tilt unit via the Serial Monitor.

#include <Servo.h> 
Servo pan_servo;
Servo tilt_servo;
int incomingByte;
void setup()
 // attach the servos and startup the serial connection
void loop()
 // check to see if something was sent via the serial connection
 if (Serial.available() > 0) {
 incomingByte =;
 // move the servos based on the byte sent
 if (incomingByte == 'e') {
 moveServo(tilt_servo, 1);
 } else if (incomingByte == 'x') {
 moveServo(tilt_servo, -1);
 } else if (incomingByte == 'd') {
 moveServo(pan_servo, 1);
 } else if (incomingByte == 's') {
 moveServo(pan_servo, -1);
 } else if (incomingByte == 'r') {
 } else if (incomingByte == '/') {
 Serial.println("pan: " +;
 Serial.println("tilt: " +;

// move the servo a given amount
void moveServo(Servo servo, int delta) {
 int previousValue =;
 int newValue = previousValue + delta;
 if (newValue > 180 || newValue < 30) {
// put the servos back to the "default" position
void resetAll() {
// put a servo back to the "default" position (100 deg)
void reset(Servo servo) {
 int newPos = 130;
 int previousPos =;
 if (newPos > previousPos) {
 for (int i=previousPos; i<newPos; i++) {
 } else {
 for (int i=previousPos; i>newPos; i--) {

Controlling the Arduino via a script

I used todbot‘s arduno-serial.c program to control the Arduino via the command line.

Get arduino-serial.c and test it out:


gcc -o arduino-serial arduino-serial.c

# test moving the camera up and to the right

./arduino-serial -b 9600 -p /dev/tty.usbmodem3d11 -s dddddddddddddddeeeeeeeeeeeeeee

Running the script via Apache HTTP Server

At this point, someone could ssh in to the computer running the camera and control it via the command line, but I wanted to have a slightly more sophisticated interface. I decided to go with a simple jQuery-powered web page that hits a CGI script served up by apache. (Note: of course, if you want people to be able to control the camera from outside your local network, you’ll need a static IP address for your machine. In that case, you should probably also make sure you set up basic authentication for your apache server.)

If you’re running OSX, apache is already installed. You can start it up by running sudo apachectl start, the config is located at /etc/apache2, and the DocumentRoot points to /Library/WebServer/ by default.

cd /Library/Webserver/CGI-Executables
vim pan-tilt.cgi

pan-tilt.cgi is the following ruby script:


query_string=`echo $QUERY_STRING`

if query_string.length != 0
`/opt/local/bin/arduino-serial -b 9600 -p /dev/tty.usbmodem3d11 -s #{query_string}`
result=`echo $?`

print "Content-type: application/jsonnn"
print "{"result": "#{result}"}n"

Finally, create the web page:

cd /Library/Webserver/Documents
vim pan-tilt.html


<script src=""></script>
<script>// <![CDATA[
            // send the input to the cgi script
            // note: sending 3x the input for every keypress, to make the movement smoother
            var submitInput = function(input) {
                $.post("/cgi-bin/pan-tilt.cgi?" + input + input + input);

            // submit input when someone presses a key down
            $(document).keydown(function(event) {
                switch(event.keyCode) {
                   case 82:
                  case 83:
                  case 68:
                  case 69:
                  case 88:
                  case 37:
                  case 39:
                  case 38:
                  case 40:
// ]]></script>

<h1>Pan/Tilt Camera Control</h1>
<div style="clear: left;">
todo: add security</div>


At this point you should be able to go http://localhost/pan-tilt.html and control the camera from there. Check out the video below!

Mini Simon Game

Another fun little project to practice my soldering skills and become more familiar with the Arduino.

Parts list:

  • Arduino Uno (SparkFun)
  • 4 push buttons (SparkFun)
  • Red/Green/Blue/Yellow LEDs (SparkFun or RadioShack)
  • PC Board Piezo Buzzer (SparkFun or RadioShack)
  • 4x 330 ohm resistors
  • 4x 10k ohm resistors
  • wire
  • PC board (I really like these) or breadboard


The buttons are wired to pins 5-8 with one node connected to +5V and the other to ground via a 10k ohm pull-down resistor. The LEDs to pins 10-13, with 330 ohm current limiting resistor. The piezo buzzer is connected directly to pin 9 and ground. For the wires going to the Arduino pins, I just wired one end to the board and left the other end hanging, so it is not permanently attached to the Arduino.


For more information about working with the piezo buzzer and an Arduino, check out CIRC06 at

// Whether we’re in “listen” or “playback” mode
boolean listen;

// Change this value to increase or decrease the number of rounds
// played before winning the game
const int num_rounds = 9;

const int speakerPin = 9;
// “A” note frequency
const int a = 1136;
// how long to play a note
const int timestep = 500;

char buttons[] = { ‘y’, ‘b’, ‘r’, ‘g’ };
int button_pins[] = { 5, 6, 7, 8 };
int led_pins[] = { 10, 11, 12, 13 };
// The frequency of all other notes is based off the “A” note
// See:
int notes[] = { a * 1.25 * 1.25,
a * 1.25,
a * 0.75
// The note we play for failure
const int fail_note = a * 4;

// an array of the buttons for this game
int play_buttons[num_rounds];

// which round are we currently playing?
int currentRound;
// what button are we on for the current round
int current_button;

// Set up the LEDs and buzzer as output,
// and the buttons as input
void setup() {
pinMode(speakerPin, OUTPUT);
for (int i=0; i<4; i++) { pinMode(button_pins[i], INPUT); pinMode(led_pins[i], OUTPUT); } initialize(); } void loop() { if (listen) { int buttonPress = readButtons(); // Check whether a button was pressed if (buttonPress != -1) { // make the button sound and light up the LED, to provide feedback playButton(buttonPress, timestep/2); // They hit the appropriate button if (buttonPress == play_buttons[current_button]) { delay(timestep); // They just played the final button for the final round if (current_button == num_rounds) { win(); return; } // They just played the final button for this round // Reset the round and switch to "playback" mode if (current_button == currentRound) { current_button = 0; currentRound++; listen = false; return; } // They're still in the middle of this round // Increment the current button and wait for next input current_button++; } else { // they didn't hit the correct button! fail(); return; } } // end listen } else { // play all buttons for the round if (currentRound == num_rounds) { win(); return; } else { // playback all the buttons for this round for (int i=0; i<=currentRound; i++) { playButton(play_buttons[i]); delay(timestep/2); } // switch to "listen" mode listen = true; } } } // During initialization, randomly choose arrays of buttons // for each round, then play a button pattern to let the user know // that the game has been loaded void initialize() { delay(timestep*2); randomSeed(analogRead(0)); for (int i=0; iVideo

Electronic Dice

This weekend I worked on a fun little project: an “electronic die”. You press the button and it randomly cycles through possible die rolls, eventually “landing” on a number.



LED layout:

d11 d13
d21 d22 d23
d31 d33


int generatingNum = 0;

int buttonPin = 9;
int speakerPin = 2;

void setup() {
pinMode(buttonPin, INPUT);
pinMode(speakerPin, OUTPUT);

pinMode(13, OUTPUT); // 1
pinMode(12, OUTPUT); // 2
pinMode(11, OUTPUT); // 4a
pinMode(10, OUTPUT); // 6a


void loop() {
int buttonState = digitalRead(buttonPin);
if (buttonState == HIGH && generatingNum == 0) {

void generateNum() {
generatingNum = 1;
int currentNum = 0;
for (int i=5; i<=25; i++) { showNum(0); delay(100); int nextNum = (int)random(1, 7); while (nextNum == currentNum) { nextNum = (int)random(1, 7); } currentNum = nextNum; showNum(currentNum); double delayTime = (.5*i + i*i*i)/20; digitalWrite(speakerPin, HIGH); delay(delayTime); } generatingNum = 0; } void showNum(int num) { digitalWrite(13, LOW); digitalWrite(12, LOW); digitalWrite(11, LOW); digitalWrite(10, LOW); switch (num) { case 1: digitalWrite(13, HIGH); break; case 2: digitalWrite(12, HIGH); break; case 3: digitalWrite(13, HIGH); digitalWrite(12, HIGH); break; case 4: digitalWrite(12, HIGH); digitalWrite(11, HIGH); break; case 5: digitalWrite(13, HIGH); digitalWrite(12, HIGH); digitalWrite(11, HIGH); break; case 6: digitalWrite(12, HIGH); digitalWrite(11, HIGH); digitalWrite(10, HIGH); break; default: digitalWrite(speakerPin, LOW); break; } } [/sourcecode]