Show Posts
Pages: 1 ... 16 17 [18] 19 20
256  Forum 2005-2010 (read only) / Interfacing / Re: battery driven: Arduino + LEDs on: November 09, 2007, 08:35:13 am
hey thanks for all the comments! - just what I needed to jog my brain into thinking about the issues in powering this piece (esp. the 9v to 5v == waste/heat issue). The minty boost stuff is great too.

257  Forum 2005-2010 (read only) / Interfacing / battery driven: Arduino + LEDs on: November 08, 2007, 09:17:38 pm
Hi -

Looking for some general impressions/responses here (since I don't have hard specs)

I am wondering @ a battery driven piece using Arduino and the Max 7129 chip driving a 48 LED matrix: what are my options? This is for an upcoming show and I don't have time to deal with/think about a sensor to trigger the sleep mode in the 7129 right now.

So I am wondering -  how long would a 9v battery last, assuming lots of LED activity (how does one calculate something like that?). I will most likely end up tethering my piece to a power supply given the short dev time but I am curious for future iterations of this project: how much do LEDs suck up? For that matter, how long would an arduino board run off a 9v battery just by itself?

Too vague, I realize but I haven't dealt with batteries/mobile before so just trying to get an idea of the questions to ask/issues involved.


258  Forum 2005-2010 (read only) / Interfacing / Re: Speaking of MAX7221/7219: Drive Higher Voltage on: October 17, 2007, 08:43:11 am
Thanks so much for this! I wouldn't have found it. Trying to make sense of the schematic now.

259  Forum 2005-2010 (read only) / Interfacing / Speaking of MAX7221/7219: Drive Higher Voltage? on: August 27, 2007, 12:02:23 am
Speaking of MAX7221/7219- has anyone had success using them to drive higher voltage/current lamps? They have an application note on it here:

I tried it last year and wasn't able to get it to work. I had some helpful correspondence with a Maxim engineer and some other folks but I may not have been using the the right mosfet for the circuit. (read: out of my depth).

260  Forum 2005-2010 (read only) / Interfacing / Re: switch on 12v light bulb on: October 04, 2007, 09:53:40 am
I used TIP120 transistors to control 16 12v auto bulbs:

based on this tutorial:

Each bulb drew an amp so having a power supply that could handle it (without heating etc) and isolating the board were important.

261  Forum 2005-2010 (read only) / Interfacing / Re: Rotary Encoder Drift?? on: August 18, 2007, 07:35:47 pm
Yeah - I put those in as a diagnostic to try to see when the interrupts were happening (and consequently making my missed pulses problem worse...)

Whew! I think I've got it working well enough now so I can move on to the next bit. And I thought the encoder was going to be the easy part...

Thanks everyone for your help and comments!! I was really stuck.

Interrupts are pretty cool! Have never used them before.

--Roy   smiley
262  Forum 2005-2010 (read only) / Interfacing / Re: Rotary Encoder Drift?? on: August 17, 2007, 10:22:13 pm
brilliant! It doesn't solve my problem entirely but at least now I have confirmation that the Wiring board is missing encoder pulses - and that the Serial.print() command makes it much worse.

I added a 10 second delay in my loop() to throttle down Serial.print() and the missed pulses/drift is much less:
0        <------ hard stop start point
-2921  <------ hard stop end point
-2225  <------arbitrary stopping point w/ lots of movement for 10 seconds
-2557  <------arbitrary stopping point w/ lots of movement for 10 seconds
-7       <------ back to hard stop start point (error)
-2929  <------ back to hard stop end point (error)
-5       <------ back to hard stop start point (error)

So it's @ a 7 step error in this short test. That's a lot better- though once I actually add code to do some work in my loop() and run things longer the error will increase over time. But hey, it's a lot better than I was getting. Thanks for the help!!

I wonder if there is a counter chip I place in between the encoder + Wiring board?


void loop()
  if  (millis() >= nextReportTime){
    nextReportTime = millis() + 10000;
    Serial.println (encoder0Pos, DEC);
263  Forum 2005-2010 (read only) / Interfacing / Re: Rotary Encoder Drift?? on: August 17, 2007, 05:12:38 pm
hi daniel,

thanks for the reply!

I have a little test rig set up with the motor/pulley mounted at one end and a pulley at the other. They are connected by a timing belt so there is positive tracking (no slippage). The encoder is built on the motor. I have hard stops on the base of this rig so that when I run the belt back and forth by hand I can stop at known absolute positions.

The errors I am seeing are not slight hand jitter - I know what you mean there - rather they are much larger - so starting at one hard stop as zero, running the belt back and forth by hand and then returning to the zero point, the encoder output will be off by 20 or 30 steps, and continue to drift if I keep moving the belt back and forth. (i.e. the drift continues to increase).

The only thing I can think is that the processor is missing pulses somehow - even though I am using interrupts. I can't see how to compensate for this in code since it doesn't seem predictable. Right now the only ugly solution I can think of is to zero out the motor through the use of a limit switch before every move but that would be a real drag (return to known zero point triggered by the limit switch).

264  Forum 2005-2010 (read only) / Interfacing / Rotary Encoder Drift?? on: August 17, 2007, 01:34:20 pm
I'm really stuck here so I hope someone can help-

This is with the Wiring board but maybe it's a more general issue that someone can tip me to.

I have a Maxon motor with a rotary encoder attached and am using the barebones code (+ using v12 of Wiring) below to try to sort out an issue with the encoder position drifting. By drift I mean that the reported position accumulates errors so that the reported position is out of scope with the actual number of motor shaft turns.

To try to isolate the issue I have the motor set up so I can rotate the shaft by hand a fixed number of turns- so I am confident that I return it to it's starting point. The greater the number of turns and the faster I turn, the more the errors accumulate.

For my project I don't need absolute accuracy but I can't have as much drift as I am seeing. I believe I have the encoder correctly wired up and the code below works so I am stumped and have spent 2 days at this trying everything I can think of.

Could the encoder be sending pulses faster than the Wiring board can handle? If so do I have any options? Would additional interrupts help? I don't need greater resolution - just less/no drift?

The only other thing I can think to try is to hold my test up to an arduino board to see if I get the same drift issue.

Thanks for *any* tips!!

--Roy (lists AT

The encoder:

int statusLED = 48;
int encoder0PinA = 2;
int encoder0PinB  = 15;
int encoder0Pos = 0;
void setup(){
  pinMode(statusLED, OUTPUT);
  digitalWrite(statusLED, HIGH);
  pinMode(encoder0PinA, INPUT);
  pinMode(encoder0PinB, INPUT  );
  attachInterrupt(encoder0PinA, doEncoder, RISING);

void loop()
  Serial.println (encoder0Pos, DEC);

void doEncoder(){
  if (digitalRead(encoder0PinB) == LOW) {
    encoder0Pos = (encoder0Pos + 1);  
    digitalWrite(statusLED, HIGH);
  else {
    encoder0Pos = (encoder0Pos - 1);
    digitalWrite(statusLED, LOW);
265  Forum 2005-2010 (read only) / Exhibition / Re: Plotter - 3 servos on: March 05, 2010, 06:49:04 pm
Nice take on a plotter!
266  Forum 2005-2010 (read only) / Exhibition / Re: Installations on: September 04, 2009, 05:53:07 pm
The cards are instructions saying "pull" or "twist" so that the participant knows how to make sound. the sensors are attached to the top to the balloons, and are stretch sensors and gyroscopes

So the sensors are on *top* of the balloons? I guess for the gyros they would have to be. I've never used gyros - which one did you use?

267  Forum 2005-2010 (read only) / Exhibition / Re: Installations on: September 03, 2009, 11:02:25 pm
Nice work! What are the cards hanging from the balloons? Is that your sensor?
268  Forum 2005-2010 (read only) / Exhibition / Re: Some robots on: September 04, 2009, 05:56:47 pm
nice work!
269  Forum 2005-2010 (read only) / Exhibition / simple 2D LED project (LED embedded drawing) on: November 30, 2007, 11:41:23 pm
Hi -

I have a new piece in the Collision Collective show which opens this week at MIT. Nothing "high tech" - the challenge was more to keep it simple.

Indicator 0x01 (Petal) 2007 • 28” x 28”, paint + electronics on paper

Indicator 0x01 is the first in a series of works that will explore the integration of simple embedded electronics in paintings and drawings.

Drawings function aesthetically in ways which are not clearly defined by any rules external to the drawing. A drawing can set its own rules and “work” in complete and exclusive reference to itself. It has no dependencies. A circuit, on the other hand, functions electronically in clearly delimited ways. The way in which a circuit is designed and the graphical patterns which result are not intended to mean anything aesthetically or visually – they are the result of efficiencies, the laws of physics, and the process of production. The visual aspect of a circuit is irrelevant to its electronic function.

In this series I am exploring these two very different forms of “function” – with programming as the bridge – and attempt to tie the “functions” of the drawing and the circuit together.
COLLISIONtwelve (C12) will take place at the MIT Stata Center Balcony Gallery
3rd floor up stairs from main entrance, 32 Vassar Street, Cambridge, MA USA
Nov 31 - Dec 16, 2007, weekdays 9-5, weekends 12-6pm
Opening Fri Nov 30 6-9pm
270  Forum 2005-2010 (read only) / News / Re: FORUM MIGRATION SCHEDULED JAN 24th on: January 19, 2011, 11:22:04 am
Good luck with the migration. I hope the new system isn't the same as the dreadful one Processing migrated too (slow, buggy on OSX, over-designed).

Pages: 1 ... 16 17 [18] 19 20