Maximum current demand at outputs OpenCockpits Mastercard

[bstikkel]

Does anybody have information about the maximum current demand at an output of the Open Cockpits Mastercard :?:. So how much mA can safely be drawn from an output.

I want to switch on and off two-colour leds for the landinggear position indicator, but...
these leds do have one common - (minus) and a + for the separate colours.
The normal switching from an OpenCockpits output is over the - (minus).
So the only solution I can think of is to use a very light relais which - no doubt - demands more current then a normal LED.

Thanks for your help ! :cool:
Bram Stikkel

[deering]

Hello Bram.

They use 74HC259N for the latches. Standard output current is 4mA. Absolute max is 25mA on a single output; absolute max through the package is 50mA.
Why not put transistors on the outputs to switch the LEDs if you need more drive?

Jim

[bstikkel]

Hi Jim,

Thank you very much for your absolute clear reply.
I considered the transistor. The problem is that I do not have the faintest idear which type of transistor I should take. If you have an advice for me, I would appreciate. The relais uses 52 mA to activate.

Thanks in advance !
Greetings,
Bram Stikkel

[deering]

Bram, which LEDs will you use?

Jim.

[bstikkel]

Ehh... I thought of switching on and off the red/green leds by 6 mini relais.
If so, I would think, only the consumption of the relais is relevant, or am I mistaken?

However, the Bicolorleds are a product bought at www.conrad.nl
The productnumber is 185000.
There is a datasheet available, which I downloaded, but do not manage to add here as an attachment :roll:

I use a 5v powersupply, from which the + goes to the LEDs and the - goes into the Mastercard.

Greetings,
Bram Stikkel

[deering]

Bram,

You should be able to drive your LEDs directly from the MC outputs. The outputs are active high; i.e. logic 1 ==> ~5V on the output pin. Ground is common.
A 470Ω resistor will limit the current to ~ 6mA. That should be good for brightness and will not be too much for the latches considering that you won't have all the outputs active at the same time. If the brightness is not satisfactory, I'm suggesting using transistors instead of relays to switch on the LEDs. NPN transistors like 2N3904 or similar will work well.

Jim

[bstikkel]

Hi Jim,

I have re-read the Mastercard connection scheme again and I must apologize for bothering this forum - you - with my question.
I really thought it had a permanent + and switched the - poles, but I now see it is otherwise.
In that case it is very simple indeed.
Sorry for waisting your time, and thanks again for your kind help.
I try to read my already have info better next time...

Greetings,
Bram Stikkel