the dissipation of a TIP102 switching an electromagnet is actually 1.5A X Vce(sat). Vce is the voltage dropped across the transistor junction at saturation. That would be about 1.5A X 2V = 3W or a little more, still mighty hot, as you have pointed out!  

Thanks for correcting me

HI I added a diagrams for driving Relays and Solenoids to the wiki, scorll down to "solenoids" on this page.

Nice the playground is getting bigger and bigger, that's very cool I might add a few things soon if I stop being so lazy and spend some time in Eagle

I tried to take a look, but there was a link problem.

Works here...

You will also need to consider power dissipation (heat). Depending of how long your electromagnets stay on and at what rate they switch on and off. At 1.5A and 24v constant, that's 36 watts of power to dissipate through the little heat sink in the back of the NPN Darlington (TIP102, TIP122) pair. You'll want to either use a decent heatsink, use a fan, use a combination (specially if you have a few of them) or look into MOSFETs which have a much lower resistance (almost none for what I read, although I am no expert, at all).

I suspect 7905 in an earlier post was a typo.

It was, my bad! 7805 is the proper IC.

I'm not smurf

Aren't we all Smurfs?

Well here's the point, find the circuits you need first

You will need something like LM7905 and two capacitors to generate regulated 5v from your 12v (all DC) source.
As for controlling the 12v for the computer, you'll probably want to look into a solid state relay (unless someone has a better idea?).
In both cases all the circuits should be widely available on the net. I'm pretty sure you can find both on http://www.epanorama.net/, but google is your friend, as always. As for a pin count, you have more than enough for the serial LCD and the relay(s). You'll probably want to had a few buttons or a keypad too for control (play/pause, next, prev, etc) and maybe an analog input or two for the lcd and volume. If you ever run out of I/Os, have a look at the Shift register tutorial and keep in mind that it is possible to do the same with inputs too. Lastely, if you haven't already I'd suggest you have a look at the Wiring electronic ref, for some quick examples.

And obviously, check the forum and playground a lot of common answers are posted there.

Have fun ^-^

Hello, I have a quick question about burning bootloaders. I have this fairly simple Serial to Parallel circuit going on using 6402 UART from Intersil (there are a couple of examples on http://beyondlogic.org). I was wondering if I could use that to burn the bootloader from the Arduino IDE? Or do I need a real parallel port? I know there are some serial programmers out there, but I'm wondering if there are more to it than just a Serial <> Parallel UART...

Thanks

P.S. I could post schematics if anyone is interested)

Hey everyone / Bonjour

This is a little late but Foulab will be hosting a basic electronics and beginner's Arduino workshop this Saturday along with a couple other workshop! Followed by another Foulab DIY party!

Be there or be square (wave)

Salut Albotech, comme je disais plutôt, inscrit toi au flux rss ou à la mailing list sur notre site web. Dès que les choses se calmes un peu j'organise quelque chose.

I might not remember to come here... you should check our website http://foulab.org/ there's a feed and/or newsletter you can subscribe to. We're on freenode also.

Magister you seem to be forgetting that arduino uses avr-gcc too Arduino describes both the board, the IDE , the bootloader and the API. I Never use the IDE, sometimes use the board, sometimes the bootloader, always avr-gcc and most of the time I still use the API Anyway, drop by the lab sometimes.

On another note, we are planning on hosting Arduino "jam sessions" for Arduiners to hang out and play. Something less formal than a workshop. How does that sound?

Hi GPX. I'm glad to tell you there is interest in Montreal. You might want to look at http://foulab.org/, we were talking about hosting an Arduino workshop soonish. We're always into having others participate. Let me know if you'd want to want more (best way to reach me is on the IRC channels #arduino or ##foulab on freenode or PM me)

That's a great idea. I've been poundering the idea of following a few of them. I have lesser classes this semester, I mgith try it out

I think this is a *great* initiative from the MIT

I might very well attend, been wanting to go to a hamfest for ever! And I'm sure it could be nice to meet other Arduino users. The only issue is that it's the same day as Critical Mass (http://www.masse-critique.org). We'll See.

Hope this will work

I have just done this using a Parallax 4x4 Keypad and the 74C922. It's a little tricky because you need to pool for changes on data available from LOW to HIGH, and then stop pooling until DA is back to LOW, otherwise it will send the key's value until you release it. There is also some issues with timing. Below is what I came up with (it also includes a little password example... just for fun). Improvements could be made, such as using a "soft delay" with millis() instead of using delay() (if you make it work, can you post an update?).

Code:

/* Parallax 4x4 Keypad using 74C922 16 Keys Encoder
 * ---------------
 *
 * Comments
 *
 * (cleft) 2005 by Matthieu Lalonde
 * <http://smurfturf.net/>
 * <mailto:mlalonde(at)smurfturf(dot)net>
 *
 */
#define BAUD_RATE 9600
#define statusLED 12

// Inputs from the 74C922 16 Keys Encoder
#define inputKey1 8
#define inputKey2 9
#define inputKey3 10
#define inputKey4 11

// The key encoder will provide HIGH on this pin when new data is available
#define dataAvailable 7

// Needed to manage inputs in a proper fashion (one entry per push)
int dataAvail      = LOW;
int lastDataAvail  = LOW;
byte keyValue      = 0;

// We need to slow down things a little, otherwise the 74C922 misbehaves
int interval       = 15;

char passwdValue[5] = {
  15, 3, 13, 1};
char passwdEntry[5];
int  entryNbr   = 0;
int  badTries   = 0;

void setup(void) {
  // initialize inputs/outputs
  pinMode(dataAvailable, INPUT);

  pinMode(inputKey1, INPUT);
  pinMode(inputKey2, INPUT);
  pinMode(inputKey3, INPUT);
  pinMode(inputKey4, INPUT);

  // start serial
  Serial.begin(BAUD_RATE);

  reportAVRState(3,1);
}

void loop(void) {
  dataAvail = digitalRead(dataAvailable);

  // Do we have a change in the state of dataAvailable or was the key just never released?
  if (dataAvail == HIGH && lastDataAvail == LOW) {
    lastDataAvail = dataAvail;
    delay(interval);

    // We do our business here
    keyValue = 0;
    keyValue = (digitalRead(inputKey1) << 3) + (digitalRead(inputKey2) << 2) + (digitalRead(inputKey3) << 1) + digitalRead(inputKey4);

    passwdEntry[entryNbr] = keyValue;

    Serial.print(keyValue, HEX);
    //Serial.println();
    entryNbr++;
    if (entryNbr == 4) {
      Serial.println();
      if (!strCompare(passwdValue, passwdEntry)) {
        Serial.print("We have a winner after ");
        Serial.print(++badTries);
        Serial.println(" times!");
        entryNbr = 0;
        badTries = 0;
      }
      else {
        badTries++;
        Serial.print("We have a loser that tried ");
        Serial.print(badTries);
        Serial.println(" times!");
        entryNbr = 0;
      }
    }
  }
  // We need to reset the state of dataAvailable
  if (dataAvail == LOW && lastDataAvail == HIGH) {
    lastDataAvail = dataAvail;
    delay(interval);
  }
}

int strCompare(char *a, char *b) {
  while (a[0] && b[0]) {
    if (a[0] != b[0]) return 1;
    *a++;
    *b++;
  }

  if (a[0] != 0 || b[0] != 0) return 1;

  return 0; //they are the SAME
}

// Reports the state of the controller via pin 13's led and serial
void reportAVRState(int howManyTimes, int leaveOn) {
  int i;

  pinMode(statusLED, OUTPUT);

  for (i=0; i< howManyTimes; i++) {
    digitalWrite(statusLED, HIGH);
    delay(200);
    digitalWrite(statusLED, LOW);
    delay(200);  
  }

  if (leaveOn) {
    digitalWrite(statusLED, HIGH);
  }

  Serial.println("AVR Initialized");
}

Here is a picture of the circuit (using SparkFun's protoshield):


You can see a video example .

[EDIT:]

It is. Happy Programming!

(I bought a USBTiny as I don't have a Parallel port EDIT: And I was lazy :p)

If you're really getting into uC's and will want to use the chip standalone (without the arduino board but with the arduino API/bootloader) it might be worth investing in a programmer kit (which ever suits your needs will do, parallel probably being the easiest. She has some nice kits, that's for sure


Don't forget you can also just make your own if you have some spare parts :p