Toggle between 2 LEDs on separate circuits in the same circuit?

[jim010]

Hello,

I am completely new to electronics! I have done many searches, and I have some solutions, but I am not understanding very well what I am reading, so I am posting here for help.

I am wanting to make a switch that turns the cooling fans for my radiators in my car on at low speed or high speed. This I can do without help. However, I want to use an OEM switch and re-purpose it for my needs, so I can avoid switches that look like they don't belong.

The switch I am using was a potentiometer. You can see it taken apart in the photos. Now I have been practicing making a replacement circuit using the sharpie method and it works. You can see this in the photos as well, although the pattern is not the one I will use. Attached is the pattern that I do think will work. Power is 12v

- When the rotary switch points down, the high speed fans will turn on and the LED will be red
- When the wheel is up, the low speed fans will turn on and the LED will be yellow
- When the wheel is in middle position, fans are off.
- When the headlights are on (turning on the blue light illumination in all the interior switches) and the fans are off, the LED is blue

Do to the small area inside the switch housing, I don't think I can go with separate LEDs, so I figured to use a tri-colour LED instead. 1 bulb, but 3 colours.

So the problem I have is to get the yellow colour when I turn on the low speed fans (i don't want to use green unless there is nothing else) I need to power both the red and the green. But I can't figure how to do this and have only the red LED light up when the high speed fan is turned on.

Another problem, is when the interior lights are on, the blue LED will light up, which is what I want. But I want the blue LED to turn off when the fans are swtiched on. I think I can do this with relays, but need suggstions. I am not understanding transistors very well.

 

[Bluejets]

Starting query would be why would one need to operate the cooling fans manually as they are already controlled automatically via temperature dependant controllers which keep the system at the ideal temperature.

 

[jim010]

Starting query would be why would one need to operate the cooling fans manually as they are already controlled automatically via temperature dependant controllers which keep the system at the ideal temperature.

I am aware. Automatic operation will not be affected. But that does not answer my question concerning the electronics of what I want to do.

 

[jim010]

I figure I can put the circuit on 2 relays on normally closed. One relay is used by the low fan circuit to shut off the blue LED and the second relay is used by the high speed to shut off the blue LED.

I am still having trouble figuring out how to get the red and green to both light up to make yellow for low but only have red light up for high.

 

[Martaine2005]

μDo you have seperate 12V live supplies for HI and LO?. Where the switch is common+ to both supplies?.(up Hi & down LO).
If so, you’ll want a common cathode RGB LED.
To get RED only on HI, put the red anode of LED with current limiting resistor on the HI side switched supply.

To get YELLOW you’ll need to connect red and green anodes together with the addition of a forward biased diode.
Connect LO side switched supply to GREEN anode and also via the diode to the RED anode.
The diode blocks the HI side turning GREEN on. (If my brain functions).
Draw it out and try to make sense of it.
Depending on the final arrangement, you can either put a resistor on each anode or just one on the cathode to GND

Martin

 

[Martaine2005]

EDIT: the above wont work with a pot unless centre is off and either side are independently supplied.
Probably better to put a resistor on each anode for equal brightness.
Martin

 

[jim010]

Thank you

Yes, the high and low are both separate power supplies.

I'll draw this out!

 

[jim010]

Yup! Makes sense to.me!

So this is what I see it as looking like:

 

[jim010]

Like I said, I am 100% new. Didn't know about diodes. Now I do, thanks!

 

[jim010]

Jus educating myself on diodes and relays, but any recommendations on what diode to use and what relay to use?

 

[Martaine2005]

I can’t comment on the relays but use ones with ample amperage for the fans. Get an idea from the vehicle fuse for it.
Any small diode will do, it’s only steering the signal to the LED. 1N4148 for example.
Don’t forget to calculate the forward voltage of the diode. Approx 0.7V. When you calculate for the resistors.
Try and view the datasheet for the LED. It will be between 1.8V and 3V probably.
And also use the engine running voltage 14.2V?, not the 12V battery.

Martin

 

[jim010]

So here is my final schematic.

I read that it does not matter where I put the 1000ohm resistor, so rather than use 3 resistors before each LED, use a single one on the common ground line?

Cheers

 

[kpatz]

That would be ok if only one LED were lit at a time, but when lighting 2 (or 3) at once they will be dimmer than when lighting 1, and the LED with the lower forward voltage may "hog" all the current and prevent the other LED from lighting at all.

It's best to give each LED its own resistor when they're wired in parallel. Another benefit, if one color is too bright you can increase its resistor value without affecting the others.

 

[jim010]

Gotcha.

Otherwise the diagram looks good?

 

[ratstar]

I dont know if itll work, but its very neat and cool lookin'
Just takes practice and you keep getting better, then you can handle more and more complex machines.

 

[Wollowstone]

You have to supply a resistor for each individual LED, otherwise, only the one with the lowest threshold voltage will light up. Here, an example of what to do, with the two leftmost LED, and what to not do, the two rightmost LED.

The circuit is made with TINA (TM), free simulator by Texas Instruments (use their site, ti.com, to download it, it is free) which automatically lights up the LED, or not, accordingly (it is not photoshopped).


NOTE: Most of the energy is lost in heat in the resistors. Preferable to use PWM (pulse width modulation) with a micro controller, imho.

 

[jim010]

So I have it all built, but I have an issue with the fans turning on. I am going from the 85 pin from the fan relay to my second relay, but it seems I loose current or voltage and the fans won't turn on.

Is there a way to solve the issue of loss of voltage/current? Thinking the resistors I put in the line to not blow the LEDs is part of the problem. I have tested the circuits individually with an LED, and they all work as intended, but when I then tie it in to the fan relays, nothing. I testged the fan relays individually and they work fine.

 

[Alec_t]

but when I then tie it in to the fan relays, nothing.

Perhaps the car's MCU which manages the fans detects the additions and refuses to power the fans?

 

[kpatz]

Make sure the resistors are only in series with the LEDs and not the relays or fans. Can you post a full schematic including where the relays are connected?

 

[jim010]