bicolor led controlled with one output

Thread Starter

secuver

Joined Jul 5, 2012
18
I would like to control a bicolor led with the output of an alarmpanel.

This alarmpanel has an output open collector who can give max. 70mA

bicolor led green/red

control voltage of the alarmpanel is 12VDC

Is their anyone who can give me a simple circuit.
In one position the led should be green
When the output is activated the led should be red.

thanks for the assistance.

Pieter
 

wayneh

Joined Sep 9, 2010
17,153
First you need a current-limiting resistor, at least about 470Ω. For testing, I'd start with 1kΩ.

Do you have any specifications for your LED, such as forward voltage drop (Vf) and maximum current (maybe 25mA)?

The open collector output is just like a switch ready to connect your LED to ground. I'm not sure how you can control 2 colors with only one switch.
 

tracecom

Joined Apr 16, 2010
3,944
You can use a small relay (SPDT) that is controlled by the output from your alarm. Connect the NC contact to the green LED and the NO contact to the red LED. You can also do it without a relay, but it's more complicated.
 

tracecom

Joined Apr 16, 2010
3,944
when i use a bicolor led i only have 2 connections?
I am assuming (in a hurry and didn't look at the datasheet) that there are only three leads on the LED: a common and one for the red and one for the green, so the common goes to ground or +V depending upon whether the LED is common anode or common cathode, and then the NC contact goes to the green and the NO contact goes to the red. You will need a relay that has a coil that doesn't draw more current than the alarm output can supply, or else you will need a driver for the relay.

I am sorry, but I have to leave now; someone here can provide a better explanation.
 

Ramussons

Joined May 3, 2013
1,059
I would like to control a bicolor led with the output of an alarmpanel.
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.....................
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Pieter
See the attachment.
You can use any CMOS gate (AND, OR, NAND, NOR, INV, Buff).
Put a Pull up resistor on your signal output (1 KΩ) and feed this setup.

You need to find the right orientation of the Bi LED to get the correct colour.

Ramesh

Correction: the resistors are 650 Ohms !
 

Attachments

Thread Starter

secuver

Joined Jul 5, 2012
18
Is it not possible to do this with just en circuit of resistors and not with extra components?

Because i would like to do this for more than one output
if this works i would like to do this 4 times 16 outputs
 

Thread Starter

secuver

Joined Jul 5, 2012
18
so if i see this right you just use a little relay with two contacts en you switch the polarity on the diode?

wich type of relay should i use to make this circuit?
 

Thread Starter

secuver

Joined Jul 5, 2012
18
if i use this circuit and the bicolored led needs 20mA and has a forward voltage of 2V

if i calculate this right then i would need a resistor of 10V/0.02A = 500Ohm

can someone confirm this?

thanks
 

Papabravo

Joined Feb 24, 2006
16,772
See the attachment.
You can use any CMOS gate (AND, OR, NAND, NOR, INV, Buff).
Put a Pull up resistor on your signal output (1 KΩ) and feed this setup.

You need to find the right orientation of the Bi LED to get the correct colour.

Ramesh

Correction: the resistors are 650 Ohms !
+12V on the VCC pin of an LS part exceeds the maximum rating and WILL let the magic smoke out. Were you thinking of a 4000 series CMOS part?
 

Papabravo

Joined Feb 24, 2006
16,772
Is it not possible to do this with just en circuit of resistors and not with extra components?

Because i would like to do this for more than one output
if this works i would like to do this 4 times 16 outputs
No. I think it is unlikely that there is a circuit consisting of resistors that will produce anything like an acceptable result on a 2-leaded bicolor. Looking at the schematic symbol you have three conditions.
  1. No current flows in either branch -- Off
  2. Current flows left to right -- RED
  3. Current flow right to left -- GREEN
Resistors are simply not capable of current steering. Where did your expectation that this might be possible with a couple of resistors come from? Was it just a vain hope or do you know something that we don't?
 

Thread Starter

secuver

Joined Jul 5, 2012
18
i only need two of the tree conditions. i don't need the off condition

it my Always be red or green and not off.
 

crutschow

Joined Mar 14, 2008
27,694
Here's a circuit using a CD4049 Hex driver. Besides the driver, 3 resistors are required. The R1 and R4 values may need some tweaking in the actual circuit to get the desired LED current values.

I used some arbitrary LED models I had for the simulation.

Note that power and ground are not shown for the CD4049.

LED Driver.gif
 

THE_RB

Joined Feb 11, 2008
5,438
It only needs 4 resistors, using a variation of Ramusson's circuit (so instead of a CMOS output it is a open collector driver with a pullup resistor.

The 4 resistor values will need to be carefully chosen to give the right 2 currents through the LED.
 
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