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ardpulsar

kalshagar - ardPulsar

Why, why, why oh why ?

It's a present for a friend who's leaving the office, I've got less than one week to build it all... hard, no room for error (-.-;)

The box will have 3 RGB led (placed East, South and West) and the USB cable at the top (North). We need USB for communication so let's use a Arduino (no time to test V-USB as initially planned). The 3 led will be able to PWM different colors at different pace, on/off, fade... well the ardPulsar box itself will just control the leds, all the decisions will have to be taken by the PC. Idea is in fact to make the ardPulsar a multi-purpose display, piloted via the control library. First purpose is show mail arrival, but since my colleague is also a professional developper, he should be able to add new things

Technical points of attention

3 leds doing different PWM with only 6 PWM port on an Arduino ? Not possible out of the box, so I'll use one of the many solutions : use transistors as logic switch and drive the 3 leds with same input and use persistance of vision.

Other options : redo the PWM manually (but way less fun)

Since I want to do time-multiplexing of the led, I have to have a quite fast PWM (default is around 500 Hz I think).
So one can force the PWM speed by changing timer settings. Ie, let's have PWM 11 and 3 run at ~4 KHz :
TCCR2B = TCCR2B & 0b11111000 | 0x02;

See these pages for details :

Communication protocol

d: 1 char in {S,E,W}, RRGGBB : color encoded in hex (2 chars per color component, so 6 chars total), DD : duration in 10th of second (hex encoded => max =~ 25s)

  • Sd : Stop led d
  • CdRRGGBB : Set led d color RGB
  • FdRRGGBBDD : Fade led d from current color to RRGGBB over DD (hex encoded, 10th of seconds)

Schema

ardPulsarSchema.png
$ 1 5.0E-6 10.634267539816555 43 2.0 50
172 208 336 176 336 0 6 5.0 5.0 0.5 0.0 0.5 Base Voltage
w 320 352 320 400 1
w 320 320 320 272 1
172 320 80 320 48 0 6 5.0 5.0 0.0 0.0 0.5 Collector Voltage
g 320 400 320 416 0
t 272 336 320 336 0 1 0.6275116430101845 0.6650758619557531 100.0
r 320 80 320 144 0 100.0
r 208 336 272 336 0 1000.0
t 288 160 320 160 0 1 0.6717118026689761 0.6846400829573815 100.0
162 320 176 320 272 1 2.1024259 1.0 0.0 0.0
r 288 160 192 160 0 100.0
172 192 160 160 160 0 6 5.0 5.0 0.5 0.0 0.5 Base Voltage
x 117 143 185 147 0 14 PWM input
x 69 372 262 376 0 14 Common cathode led 1 control
x 390 371 583 375 0 14 Common cathode led 2 control
162 608 176 608 272 1 2.1024259 1.0 0.0 0.0
r 496 336 560 336 0 1000.0
t 560 336 608 336 0 1 0.6275116430101831 0.665075861955753 100.0
g 608 400 608 416 0
w 608 320 608 272 1
w 608 352 608 400 1
172 496 336 464 336 0 6 5.0 5.0 0.5 0.0 0.5 Base Voltage
w 320 176 608 176 0

This is just an extract for the idea (explained for 1 color component, so do this x3):
  • The PWM for the color (say Red) is shared for all the led, using a NPN transistor as a switch. Current source is directly the %205 V of the Arduino board, the PWM pin just sources a few mA
  • The second transistor at the bottom is a switch that emplables the cathode to or not, hence let the led turn on

So you need 3 transistors for the PWM (R, G, B) %20 1 transistors per RGB common cathode makes 6 transistor total in my case.

The top resistor (100 ohm) might be a bit too strong when 3 led are driven (drops around 10-15 mA) so turning it to 50 ohm gives a nice 20 mA to the leds (just put another 100 ohm in parallel to drop the summed resistance to 50 ohm).
All content on this site is shared under the MIT licence (do what u want, don't sue me, hat tip appreciated)
electrogeek.cc ~ Formerly known as Kalshagar.wikispaces.com (AlanFromJapan [2009 - 2019])