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5371  Forum 2005-2010 (read only) / Interfacing / Re: 32x32 on: September 30, 2007, 10:59:11 pm
Someone should make a plug-in current monitor for USB...
5372  Forum 2005-2010 (read only) / Interfacing / Re: 32x32 on: September 29, 2007, 02:44:33 pm
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The 595 doesnt multiplex so every single LED is on all the time.
erm - the 595 is a multiplexer, 3 inputs - 8 outputs.  smiley-wink
While the 595 has three control signals, it is not a "multiplexer" in either the digital logic sense or the display driver sense. The 595 is a shift register with an output register; a form of serial to parallel to converter.  It's outputs stay in one state till changed, so LEDs connected to those outputs ARE "on all the time."  You CAN multiplex (display sense) a display connected to 595s; a single 595 could drive a 4x4 array of 16 LEDs, and two could drive an 8x8 array; the rate at which serial data can be clocked into teh 595 is typically much faster than the display update rate for a multiplexed LED display...
5373  Forum 2005-2010 (read only) / Interfacing / Re: Driving 8x8x3 outputs on: September 26, 2007, 05:22:57 am
The same eBay vendor has some pretty nice mini-SD sockets...

5374  Forum 2005-2010 (read only) / Interfacing / Re: Driving 8x8x3 outputs on: September 26, 2007, 01:57:09 am
By the way, one of my favorite eBay sellers is selling an interesting 16-channel LED driver chip with built-in constant current source:

http://cgi.ebay.com/10-LOT-CONSTANT-CURRENT-LED-DRIVERS-5V-16-CH-SRC-DIP-30_W0QQitemZ230175586970QQihZ013QQcategoryZ50913QQtcZphotoQQcmdZViewItem

Pretty cheap, too.
5375  Forum 2005-2010 (read only) / Interfacing / Re: Driving 8x8x3 outputs on: September 22, 2007, 03:06:35 pm
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My numbers say 1.2A.

8*8*3*0.02 = 3.84, yes?

You might consider partial multiplexing.  doing 64x3 (one multiplex plane for each color) would cut the number of resistors by 2/3 (since you'd only be driving one color at a time, you'd only need the resistor in the common line.)
5376  Forum 2005-2010 (read only) / Interfacing / Re: Driving 8x8x3 outputs on: September 22, 2007, 01:50:39 am
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Keep in mind that I'm using 595's. No crappy Multiplexing for me. Smiley
The LEDs will be on all the time if active.

Keep in mind that you'll need like a 4A power supply if you want to have them all on at the same time.

100ohms and a 5V supply will give you a max of 50mA through the LEDs, assuming that they're all zero volts.  So that should be reasonably safe.  I don't think red is inherently BRIGHTER so much as that it has a lower voltage drop and so gets more current for the same resistor (and therefore RUNS brighter...)

I don't think you can use a single resistor in the common leg unless you want the brightness to vary depending on how many of the three internal LEDs you have on.  The effect may be worse than that; turning on the Red with its lower voltage may "steal" current from the  other colors and make them go off.
5377  Forum 2005-2010 (read only) / Interfacing / Re: Help With Servo's on: September 25, 2007, 01:58:43 am
It certainly looks like a speed mismatch.   Are you using the "Serial Monitor" of the arduino environment to talk to it?  If so, did you notice that the monitor and the download speed have separate defaults?  If not, you might try using it till you successfully see your ready message...
5378  Forum 2005-2010 (read only) / Interfacing / Re: Arduino and lots of servos on: September 22, 2007, 03:36:50 pm
A key to driving a large number of servos is that they don't all need have their input pulse "on" at the same time.  In a "real" RC system, the transmitter/receiver will deliver a pulse for servo 1, followed by a pulse for servo 2, and etc, up through about servo10.  Since each pulse is a max of about 2ms (including some off time to allow the logic to step to the next servo), you get to manipulate 10 servos, each every 20ms, but only one is getting a pulse at any given time.  Since 20ms is still 50 position updates/second, all the servos appear to move simultaneously.
From a microcontroller perspective, this means that you can control about 10 servos with a single timer "event."
Code:
loop() {
  if (hires_time() > servo_stoptime) {
    /* This servo has it's pulse, step to next */
    whichservo += 1;
    if (whichservo > N_SERVOS) whichservo = 0;
    servo_stoptime = hires_time()+ servo_db[whichservo].pulsewidth;
  }
/* Other code.  better not take too long, or the servos will jitter */
} /* end loop() */
The need for your other code in loop() to run for "small" amounts of time compared to the resolution of the servo position pulse is a problem, and it's tempting to tie this whole thing to a hardware timer and an interrupt service routine ("advanced" programming, rather out of the arduino space.)  And there's more; each timer on the AVR can generate three separate timer event interrupts, and there are three timers and only one of those interrupts is in use.  So I figure that IN THEORY, an arduino would not have too much of  a problem driving 80 servos, while still having time to do other things.  (it'd average 4 interrupts per millisecond, which is a significant number, but not awful...)  Not having 80 pins might be an issue  ;D
5379  Forum 2005-2010 (read only) / Interfacing / Re: Arduino and lots of servos on: September 20, 2007, 06:58:34 pm
It should be possible to write timer-based service code (breaking at least one PWM output) capable of driving a large number of servos while still leaving plenty of time for other code.  I'm not sure that it's worth potentially breaking the "wiring" compatibility and introducing possible cpu dependencies to do it, though...
5380  Forum 2005-2010 (read only) / Interfacing / Re: electromagnet on: September 19, 2007, 11:05:32 am
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I was using a PNP transistor.

Your schematic shows an NPN, and if you were to put a PNP in the same place, your circuit would be wrong.  Normally NPNs (as you show) are inserted in between the load and ground, and turned on with +V, while
PNPs are inserted in between the  +V rail and the load, and are turned on by GND (but will expose the pin
to V+ - Vbe, which is not good if you're swithing high voltages with a 5V micro.

Most voltage regulators have "over current" and "over temp" protection, and will turn off (or "something") if you draw too much power from them...
5381  Forum 2005-2010 (read only) / Interfacing / Re: electromagnet on: September 17, 2007, 03:59:48 am
What kind of transistor?  A 1.5V battery is pretty low in voltage to be switching this way; a typical transistor will lose .3V or so, and a "darlington" (which is common for power switching) will lose about 1.2V, which won't leave very much left for your electromagnet (or for an LED, which will usually need at least 2V.)
5382  Forum 2005-2010 (read only) / Workshops / Re: Any workshops in San Jose California?? on: May 08, 2010, 04:47:31 pm
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Haker Dojo charges a $100/month.
As does TechShop (approximately), for "membership."  Which is not the same thing as requiring that you be a member in order to attend a workshop that might be presented there.  (not that it means there ARE any such workshops :-( )

I dunno.  Designing a "workshop" is HARD.  Especially given the wide range of user expertise that such a workshop is likely to have show up...
5383  Forum 2005-2010 (read only) / Workshops / Re: Any workshops in San Jose California?? on: April 17, 2010, 03:46:21 pm
There are arduino classes at Techshop (menlo park), and I think there is some presence at Hacker Dojo (Sunnyvale), though neither is specifically Arduino focused...
5384  Forum 2005-2010 (read only) / Workshops / Re: Bay area Arduino meet @TechShop 9/25/2010 6-9pm on: September 25, 2010, 07:55:03 pm
Heh.   if this had been a day later, we would have had more to talk about...
5385  Forum 2005-2010 (read only) / Workshops / More EAGLE events (Webinars, this time.) on: May 18, 2010, 12:35:55 pm
element14 is running 3 EAGLE introductory webinars. I'd appreciate it if you could pass on the message to anyone you'd think would be interested

English

May 19th at 12 pm CDT
http://www.element-14.com/community/events/2584

Chinese language:

Thursday, May 20, 2010 12:00 pm
Singapore Time (Singapore, GMT+08:00)

Event address for attendees: https://premierfarnell.webex.com/premierfarnell/onstage/g.php?t=a&d=848295613

German language:

Thursday, May 20, 2010 12:00 pm
Europe Summer Time (Berlin, GMT+02:00)

Event address for attendees: https://premierfarnell.webex.com/premierfarnell/onstage/g.php?t=a&d=841081781
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