Yeah for crucial timing applications you'll definitely want a phototransistor measured digitally.

Take a look at the attachinterrupt() library, it should work perfectly for you.

Also, note that most phototransistors respond to a very narrow frequency band, and lasers also put out a very specific frequency, so you'll have to find a pair that matches.

I have written a sketch to do this, instructions and download here:
http://blog.wingedvictorydesign.com/2009/03/20/receive-dmx-512-with-an-arduino/

Let me know how it works for you!

I took another look at the built-in resistors, and you're right, they are 1k on mine.  The point being to limit the amount of current going through the diode so that you don't burn out your LED, of course.

Also, the capacitors are connected across +5V to ground, although since the reset switch is also connected to ground they are in a sense connected to the reset switch.
http://www.ladyada.net/images/pshield/v5schematic.png

w.r.t. the switch, remember that you can connect a ~10Kohm pullup resistor between +5V and the sensor side of the switch, and thus have a logical 1 when the switch is unpressed, and a logical 0 when it is pressed.  Quite handy when you need a stand-in for some other sensor that you haven't purchased yet.

btw, make sure you don't solder on the header pins on the wrong side of the board.  I did that when I was wiring up mine and they're a real pain to get off if you do them wrong :.

--The caps:
The capacitors tend to smooth out ripples in the supply voltage, which remain after you have converted AC (bumpy) to DC (flat, ideally).  They can be omitted, if you like, as they supplement the capacitors on the Arduino board itself.

--The LEDs:
Are hooked up to 100ohm resistors, not 1K (at least on my protoshield).  You will have to solder a small piece of wire into the holes indicated on your instructions, and then you can simply connect that wire into any pin on the board, and if there's voltage there, the LED will light up.  Handy.

--The switches:
    The second switch is connected to ground, as I remember.  You will have to solder a wire into it to be able to use it.

--ICSP:
useful if you don't want to program your arduino via usb, I think.  I've never used them.

--The three additional female headers:  one is connected to +5V, the other two to ground.  Handy, because otherwise you only have one pin of each type, so you'd have to run a wire out to a row on your breadboard.

I don't know what instructions you're using, but the ones on the Adafruit website are excellent, and explain all this:
http://www.ladyada.net/make/pshield/

Hope this helps.

by the way, from searching I found this thread:
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1200869072/4#4
but I didn't see any resolution there.  

Hi All,
     I'm trying to interface the Arduino to a device with a 250Kbps baud rate, and display the results in the serial monitor in the Arduino software.

Is there a way to set the Serial Monitor in the software to 250000bps?

Thanks for the help!

What is the purpose of the guard pin (pin 10)?  The code seems to work just as well without it...

Hi All,
    I made a combination Theremin/Synthesizer for my sister, who's a musician, and I'm pretty happy with the way it came out.  It has the following features:

• Four octaves of continuous pitch variation by moving your hand nearer or farther from an ultrasound sensor
• Digital volume control
• Continuous waveform variation–can generate a pure sine tone like a classic theremin, or one with overtones, which sounds like an 80's synth organ.
• Spectral glide–similar to a Wah pedal or the instrument used in Peter Frampton's 'Do You Feel Like I Do'
• Decay/Sustain–envelope shaping to play notes
• Distortion–sounds like the guitar effect.
• Blue case lighting with 'heartbeat' effect

It's powered by a 5V/16Mhz Arduino Pro 328.  Pitch control is done with ultrasound, the other effects by controls which move an LED nearer or farther to a photoresistor.

I've done a pretty extensive write-up of the hardware and software on my blog, might be helpful for someone who's working on a similar project.

http://blog.wingedvictorydesign.com/2009/06/20/arduino-thereminsynth-final-walkthrough/

 
Max

btw, the internal resistors are pull-up only.  So doing:

Code:

pinMode(pin, INPUT);      
digitalWrite(pin, LOW);        

will not do anything for you.

If you're going to use a transistor, you'll have to get a pretty beefy one to handle the 50W or whatever turn signal bulbs.  My guess is that this LC circuit you found actually drives a relay.

The relay is what makes the click-click sound on a turn signal, so if you're not hearing that, the relay or a connection leading to it has failed.  Turn signal relays are usually well-stocked at Autozone and cheap, so I'd try replacing it and see what you come up with before I tried to make a custom circuit.

Ah gotcha, thanks for the clarification

I thought the maximum input voltage on the arduino was 12V?  You said that you were powering it via 24V DC.

I read in hack-a-day a couple months ago about a robot cobbled together with an Android G1 headset and an Arduino.  The control interface between the two was DTMF (DFMT?).

Here's the link:
http://macpod.net/misc/android_robot/android_robot_media.php

Also, soooo cute.

The adafruit arduino tutorials are also pretty good:

http://www.ladyada.net/learn/arduino/lesson0.html

Or if you have an unused lighting dimmer laying around, you can salvage it out of that.

The older dimmers will be resistive, which won't help you, but the new ones they sell at Home Depot all have triacs, and also the shielding hardware so that you won't be broadcasting in the AM range, if you care.