Tuesday, October 28, 2014

PWM controlled RGB scanner lamp

PWM controlled RGB :  old scanner lamp

>>> part two available here <<<
>>> part three available here <<<

Cool things can be done with old trashed electronics, today an old All-in-One printer/scanner from HP will be disassembled on the hotel of science *sigh*

There are a very few things about recycling scanner lamps on the internet, mostly incomplete information. This post ins't to make exhaustive WIP, but giving a few more leads towards success...

This WIP will be based on the following : 

  • LANp (which uses a 5 pins RGB lamp instead of 4 like there is on my HP one)
  • instructables.com "printer scanner light" (that doesn't talk about PWM)
  • instructables.com "Scanner light hack" (that uses a battery instead)

1/ Finding the positive pin and the RGB ones
on these lamps, there is 4 pins used, one is the positive (usually +5VCC, but i'm not sure if 5V is (it was not in fact) really the nominal voltage for this specific HP lamp)...

Canon lamps have 5 pins, so it can't help to find which of the 4 is which ...
A comment on instructables gave the following for HP lamps : 

I made some tests and it appeared to be right!
on mine it is Blue-Green-Red-VCC

Though, the pins here are too small for the available wires and soldering iron... Turned out with continuity tests that the 4 pins at the left are linked to these on the slot... but in a reversed (messed) order!

  • VCC
  • Red
  • Blue
  • Green

2/ Soldering wires
While taking apart the VHS-PSU i got some ribbon cables, a new life for one of them : 

from left-to-right : VCC, Red, Blue, and Green. For easier management, i simply inverted the order while soldering so that i can get RGB sequence at the other end :

 3/ Insulating with hot glue to make sure nothing can short-circuit

4/ Building and insulating the plug 
(VCC is took one pin after on purpose to know where is VCC, and the 3 RGBs.)

5/ Results

6/ Testing and... failing

Worked perfectly as long as it was powered by an old 9V battery (provides only about 5V said my voltmeter)

Red and Blue burnt as soon as i tried a 5VCC supplied by a computer PSU... protected by an adjustable resistor ... accidentally set to 0 ... (who said: "You're Dumb Bro!" ???)

Of course, Don't NOT use without current limiting resistor (you may use ledcalc.com to easy find the one you need)

So this WIP is locked until i find another lamp and an Arduino chip to fully control it with PWM.

Read part two here : getting another scanner lamp.