lsdweb
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| posted on 16/11/07 at 10:31 PM |
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Tri colour LEDs and switchable maps?
Hi All
I'm using the K3 version of the Emerald ECU and three switchable maps. The switching for this is as shown below. I'd like to have a tri
colour LED to indcate which map is currently enabled.
Anybody got any ideas on how to do this simply? This should be simple but I must be missing something!
Regards
Wyn
 
Rescued attachment switchable.jpg
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MikeRJ
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| posted on 16/11/07 at 10:48 PM |
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There is not way to do it passively, i.e. just the LED and a few resistors, because the amount of current required to light an LED would significantly
load the 1k pullup in the ECU (which could cause it to think the wrong map is selected).
However it's certainly doable with relative simplicity and at low cost, using comparators. I'll post a circuit if you would like to have
a go.
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lsdweb
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| posted on 16/11/07 at 10:53 PM |
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Hi Mike
If the circuit is relatively simple, I'd have a go - I can solder and there's a local Maplins!
Thanks
Wyn
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MikeRJ
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| posted on 17/11/07 at 01:05 AM |
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quote:
Originally posted by robocog
..unless the 3 way switch you use can be stacked (like wafer jobbies) or has another set of contacts?
Very good point, 10/10 for lateral thinking 
You can get small toggle switches with a center off position and two poles quite easily.
[Edited on 17/11/07 by MikeRJ]
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ghuncha
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| posted on 17/11/07 at 06:10 AM |
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i think this will work, please if there is some problems do let me know, i am still on the noob stage.....
the negative to the comparators is output from the switch and goign to the ecu
[Edited on 17/11/07 by ghuncha]
[Edited on 17/11/07 by ghuncha]
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lsdweb
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| posted on 17/11/07 at 09:21 AM |
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Thanks Guys
The two way, double pole, cenrtre off switch sounds like the option!
ghuncha - I wouldn't have a clue if your circuit worked! Thanks for the efforts though!
Regards
Wyn
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lsdweb
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| posted on 17/11/07 at 09:37 AM |
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Although how do I get a two position switch to operate a three colour LED?
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MikeRJ
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| posted on 17/11/07 at 06:22 PM |
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When you say a three colour LED, what I had in mind was a "bicolour" LED that physically contains two LED chips. By driving either one,
or both chips together you can get three colours. This makes the wiring very simple indeed.
I made a very simmilar circuit to ghuncha's but using a bicolour LED (only two comparators/one chip) if you still want it.
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MikeRJ
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| posted on 17/11/07 at 06:46 PM |
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This is how you would drive a true Tricolour LED from a two position (center off) switch. This relies on the differing forward voltages (Vf) of the
LEDs. Putting an LED with a lower Vf voltage in parallel with one with a higher Vf will turn off the one with the higher Vf.
Typical the Vf's of a tricolour package are:
Blue 3.3v
Green 3.3v
Red 2.0v
As you can see the green and blue LEDs in tricolour packages have very similar foward voltages which would make this scheme fail. To work around this
problem we use an extra diode (1N4148 or 1N4001 etc will be fine) to increase the Vf of one LED by around 0.6 volts.
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lsdweb
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| posted on 25/11/07 at 11:04 PM |
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MikeRJ
I used your simple option on a bicolour LED - works a treat! Photos of the dash/wiring to follow soon.
Thanks!!!!
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MikeRJ
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| posted on 27/11/07 at 01:49 PM |
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Glad it worked ok for you!
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lsdweb
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| posted on 27/11/07 at 08:56 PM |
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And here it is!
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