Need help with DIL and LEDs

[BeechSim]

This will be fairly simple to many of you here, but new to me.

I'm building a flight simulator.

I have an interface card with built in current limiting resistor That will power one LED at 5vdc max 20ma

I want to connect three LEDs to the output each is 5vdc 30ma.

I know that I need a relay. I think a DIL or similar.

I don't know what type because I have no experience of these. I did think of putting resistors in to limit the current but then surely I will have very dim LEDs.

Ideas? suggestions ?

Dean **broken link removed**

 

[justDIY]

Dean

you don't need a relay - you need a transistor

5 volts is pretty high for such a small amperage - double check your specs on that LED... perhaps you're using pre-wired LEDs which have built in resistors?

if your power source is limited to 5 volts, you will wire your LEDs in parallel to the transistor.

if have more power available somewhere (say 12v) [again, check the specs on yer LEDs], you can wire the LEDs in series to the transistor.

check out this site for how to wire a led to a transistor
https://www.iguanalabs.com/1stled.htm

your single output card would then turn the transistor on and off, much like a relay.

 

[BeechSim]

Hi,

And thanks for the reply. I may be mistaken then in what I have bought.


Order Code UK21X: High Efficiency Red
Kingbright description: L-793ID
Forward current max.: 30mA
Forward voltage max.: 2.5V
Reverse voltage max.: 5V
Wavelength @ peak : 627nm
Power dissipation PT: 105mW
Light output min.@ 20mA: 40mcd
Light output typ.@ 20mA: 100mcd

Order Code UK22Y: Green
Kingbright description: L-793GD
Forward current max.: 25mA
Forward voltage max.: 2.5V
Reverse voltage max.: 5V
Wavelength @ peak : 565nm
Power dissipation PT: 105W
Light output min.@ 20mA: 20mcd
Light output typ.@ 20mA: 60mcd


These are the specs for the LEDs

In the manual for the Card is says "The outputs are connected to +5v supply via a 470 ohm resistor and can drive an LED directly without any additional LED series resistor. A maximum of 20 mA can be drawn from each output. Note the current limiting resistor is already mounted on the card"

Maybe I have got it wrong, I've looked at these specs and thought it was OK, then I have to admit I read a little more deeply.

Dean

 

[audioguru]

The card might have a 470 ohm resistor from 5V to light an LED with only 5.3mA for a 2.5V LED. Then a transistor shorts the LED to turn it off.

 

[BeechSim]

So,

Let me get this right. With the LEDs that I'm using, they should only be drawing 5.3 mA each ?

I checked the connections today and with the LED connected I read 2v and with it disconnected I read 5V at the output from the card.

Sorry to sound like such a dummy, but I am worried about drawing too much current from the card if I connect 3 LEDs to its output, which I would like to do.

Thanks all for your help.

 

[audioguru]

The manual for the card says, "The outputs are connected to +5v supply via a 470 ohm resistor and can drive an LED directly without any additional LED series resistor. A maximum of 20 mA can be drawn from each output. Note the current limiting resistor is already mounted on the card".

The manual doesn't make sense. A dead short at the output of a 470 ohm resistor from a 5V supply will draw a current of only 10.6mA. The current from each output will never reach 20mA unless the load is connected to a negative supply.

If you connect 3 LEDs in parallel, they will unevenly share the 5.3mA available to them.

 

[justDIY]

why can't a simple transistor be used as a switch (powered by the weak output of this card, whatever that may be), to provide full current to the three leds?

in one of the pictures, I saw an ATX power supply ... if that is still available, you have plenty of power - wire your LEDs up in series to the +12V rail, with an apporiate resistor, and they will all share the current equally, which should result in nice uniform brightness.

 

[BeechSim]

Ok,

It's clear to me now. And with the information everyone has given to me I can sort it out. I will finally be able to get "3 greens" for my landing gear.

Thanks all