Powering an array of leds from one single MC output line

[Jackpilot]

Alessandro

Good luck and let us know how you get on. I will probably have to go the same route to provide enough power to light up the bulbs in the pedestal fire handles

Regards

David

Super bright leds work well too in the FH and can even blink (with a hidden blinking led in serie). Much lower load altogether.

[fordgt40]

Jack

Now thats a great idea - I did not think about putting a small blinking led in series. That solution would be handy elsewhere as it is difficult to get high output blinking leds

Regards

David

[fweinrebe]

Yes, that is what I was suggesting with a darlington pair. I think you need to get an IC no ULN2004. This is an array of 7 transistor pairs on a chip that allows each output a current of 500ma. Basically, you connect your OC output, probably through a diode, to the IC ULN2004 input. The ULN output will give a output voltage of between 5-12v dependent on what power source you give the chip.

Have a look at this card. It is actually for a PIC development board, but it could be used for what you are referring to. It uses a ULN2804 and has typical power loads totalling over 260 W (350 mA x . http://www.mikroe.com/en/tools/mikrodrive/.

[pdpo]

Just for your info,

mastercard can drive a LED with a resistor in series to limit the current through the LED.
20mA is a rather high value for a normal LED but for the superbright LEDs the current can
be higher.
Measurements on an output have revealed also an internal resistor on each output. This
results in the fact that on a 5 Volt output 2 leds in series can be connected without the
use of a resistor and the current will be limited enough by the internal resistance.
When you need to drive more then two leds then you could use two optocouplers connected
with their leds in series. This way the MC output will light the two leds in the optocouplers which can drive then a 12 Volt line with 4 leds in series with a small current limiting resistor.
this way you can drive 8 leds from one MC output.

Greetz Peter

[weyes]

Thank you everybody for your help.

In the mean time I have discovered that the button is splitted horizontally. The yellow line (warning) is at the bottom; the red line (caution) is in the upper side.
This triggered a whole refactoring of the button. In particular I can put in each of the 2 lines no more then 2 LEDs because in fact I do not have enough room for more then 2 LEDs.

Initially I try feeding the 2 LEDs with the solution prosed by Peter (pdpo).

I need some time now for the connection of the cables but I'll keep you up to date.

[weyes]

Just an update...

The button is ready. The two LEDs worked as Peter suggested and the final result is even better then I thought... I am quite surprised of the final result, much better then I could thought. I have taken some pictures and when I have time I will post a kind of tutorial in my blog and add here the link.

However, the problem of lighting several LEDs at once is waiting me for the gear panel. But that's another history...

[weyes]

I have put some photos describing the work I did in my blog. If you're curios you can red the last post of the blog.

The cost of the button is around 10-12 euro. I guess this same solution could be used for korry switches too.