Electronics help - using transistor as relay

[Sundayjumper]

I'm sure this is quite simple, and I'm sure I used to know this stuff, but that was a long time ago, and other options may have become available.

I'm trying to repurpose a Toyota indicator relay. It requires the inputs to be pulled to ground to activate it. I want to activate on presence of +12V. So I need some kind of NOT function.

This is trivial with a relay, and I've already tested it like that to confirm the logic. But the current draw in this case is so miniscule - I measured 20 microamps - that a relay is total overkill. And big. With some kind of solid state solution I can probably squeeze it into the existing enclosure.

So what's the simplest (and I'm expecting this to be cheap!) way to pull to ground on presence of +12V ?

cf18_adjustable_flasher.jpg (24.31 KiB) Viewed 848 times

[DeskJockey]

I've no idea, but I'm interested to know what you're fixing.

[Sundayjumper]

Nothing weird ! I want LED indicators in the 406 because they're crisper, but if you just chuck in LEDs (I bought THESE) you get "hyperflashing" because the current draw is much lower, and the flasher relay doesn't work properly. You get the same if one of your regular bulbs blows. You can put a resistor in parallel with the LED to being the current draw back up but that's a cludge and completely ruins one of the points of LEDS - that they're more efficient.

There's LED-specific flasher units available but none I could see for this car. And if there were it'd be £stoopid because obviously. However I found that a Toyota unit (diagram above) has identical functionality aside from this earth / 12V difference. So I bought one and a little relay module to try it out. I made this and it works:

IMG_1704.jpeg (107.61 KiB) Viewed 784 times

A fringe benefit that I didn't expect was that this unit also does that three-flash thing if you just blip the stalk. Cool

The relay module in the middle is the bit I wanted to simplify. Should be easy enough ? It's rated to switch 10A, I only need a few milliamps.

[JonMad]

Not sure, but maybe this? https://www.dummies.com/article/technol ... it-179357/

[Jobbo]

I think the transistor should do the job on its own, though that's effectively what a NOT gate is I guess. Here's a 'transistor switch' which looks uncannily like the NOT gate in Jon's link: https://learn.sparkfun.com/tutorials/tr ... i-switches

[IanF]

https://www.scuding.com/Shop/en/ecu-sol ... s-ecu.html

Some cable options lower down

[Sundayjumper]

https://www.scuding.com/Shop/en/ecu-sol ... s-ecu.html

Some cable options lower down

Already seen that. I am not spending £300+ to turn a light on and off

Current spend is £11.47 for the flasher module + £3.89 for the relay board. I’m expecting a transistor to be a matter of pennies.

[IanF]

https://www.scuding.com/Shop/en/ecu-sol ... s-ecu.html

Some cable options lower down

Already seen that. I am not spending £300+ to turn a light on and off

Current spend is £11.47 for the flasher module + £3.89 for the relay board. I’m expecting a transistor to be a matter of pennies.

Yes, but then you can “enhance” it in other ways..

[GG.]

Steve, earlier today...

[Sundayjumper]

Steve, earlier today...

I'm slightly ashamed of myself here, but it had already crossed my mind to put mood lighting in the engine bay

[GG.]

Steve, earlier today...

I'm slightly ashamed of myself here, but it had already crossed my mind to put mood lighting in the engine bay

I think that would look good actually

I'm sure you could have it on a switch and just on when desired - best make sure you've got a clean engine bay though...

[integrale_evo]

Make it flash and illuminate a big “danger to the manifold” warning as you approach the redline