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61  Forum 2005-2010 (read only) / Interfacing / Re: Best method for precise distance measurement on: May 29, 2009, 05:12:43 pm
Thanks for the advice.  I tried heterodyne and phototransistor sensing, but couldn't really get them to work for me.  Finally I ponied up the $35 for a parallax ping.  It was more money than I wanted to spend, but I can't argue with the results-- it's accurate, stable, and even linear.

Also, if you do pulse sensing with an external interrupt pin, the processor load is minimal.
62  Forum 2005-2010 (read only) / Interfacing / Best method for precise distance measurement on: May 26, 2009, 03:17:15 pm
Hi All,
      I need to detect distance fairly precisely (detect an object like my hand within 1/4" in the range of 1-24in), and I'm wondering what the best method to pursue would be.  Here are the options that I'm aware of:

Ultrasound (via the Parallax Ping sensor, e.g.)
IR emitter/detector
capacitance sensing (via, e.g. the Capsense library)
heterodyning (like a theremin)

I tried capacitance sensing, but even after I set it up with shielded cables and so on it doesn't appear to have the range or the precision or the stability I want.

In an ideal world, the sensor module would be precise, stable, have a light processor footprint, and if possible linear in nature.

Any ideas?  I don't mind buying an IC to do the job, I'm just unsure where to go next with this.

63  Forum 2005-2010 (read only) / Interfacing / Re: laser detection on: May 28, 2009, 03:00:59 pm
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.
64  Forum 2005-2010 (read only) / Interfacing / Re: DMX arduino on: April 30, 2009, 03:38:50 am
I have written a sketch to do this, instructions and download here:

Let me know how it works for you!
65  Forum 2005-2010 (read only) / Interfacing / Re: Protoshield on: March 04, 2009, 11:51:08 pm
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.

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 :smiley.
66  Forum 2005-2010 (read only) / Interfacing / Re: Protoshield on: March 04, 2009, 10:35:38 pm
--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.

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:

Hope this helps.
67  Forum 2005-2010 (read only) / Interfacing / Re: custom baud rate in serial monitor? on: February 27, 2009, 06:00:50 pm
by the way, from searching I found this thread:
but I didn't see any resolution there.  
68  Forum 2005-2010 (read only) / Interfacing / custom baud rate in serial monitor? on: February 27, 2009, 05:59:43 pm
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!
69  Forum 2005-2010 (read only) / Exhibition / Re: Arduino as Capacitive Sensor on: May 20, 2009, 07:36:25 pm
What is the purpose of the guard pin (pin 10)?  The code seems to work just as well without it...
70  Forum 2005-2010 (read only) / Exhibition / Arduino Theremin/Synth on: June 25, 2009, 08:52:14 pm

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.


71  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: internal pull up resistor? on: May 25, 2009, 12:54:02 pm
btw, the internal resistors are pull-up only.  So doing:

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

will not do anything for you.
72  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Recreating a motorcylce flasher on: May 25, 2009, 01:02:25 pm
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.
73  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Battery backup on: May 29, 2009, 05:06:49 pm
Ah gotcha, thanks for the clarification
74  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Battery backup on: May 27, 2009, 03:23:40 am
I thought the maximum input voltage on the arduino was 12V?  You said that you were powering it via 24V DC.
75  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: DTMF outputs on: May 27, 2009, 03:32:39 am
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:

Also, soooo cute.
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