I am thinking of doing some LED lighting in my car (doing a custom dash i hope...) I thought it would be really cool if i make it so it varied with the RPM's so as the RPM's went up so did the brightness of the LED's. Is there such a device/variable resistor available? They use something similar in controlled N2O systems where it ramps it up as the rpms go up.

 

what kind of voltage or signal is sent to the tach?

 

A variable frequency is sent to the tach.

I dont know of any device that changes brightness with RPM, but it could be done. For running right off of the tach wire, you'd need some type of frequency to voltage circuit/device. Then just wire up an LED and a resistor - the LED should change brightness. That's putting it really simple though.

Wait, hold on, you have a variable voltage right on the meter of the tach, this is after the tach wire, after the electronic stuff, inside of the gauges. Those two wires that connect directly to the tach's meter would give your variable voltage. What it is, dont know, a voltmeter would tell you. You'd have to wire up a transistor or some kind of circuit so you wouldn't affect the tach's output. I wouldn't put in a resistor and LED right there across those two wires.

 

I hate to say it but if you’re asking this question, the answer is probably going to be out side your abilities at the moment. I’m unaware of anything pre-built to do this. Unless you can find someone that has done this with your specific application you’re going to have to do a lot of homework and learn home brew electronics. You’re not going to want take the signal from right at the movement. It’s going to be hard to confirm if there would be any adverse affects from loading. Depending on how they’re driving the movement, even a 10 megohm per volt meter could load things. The most elegant way to do this would be to take the tach. signal and drive some kind of PWM led driver. The advantage to this is there are some vary promising off-the-shelf ICs out there right now that would do most of the work in a vary nice small size. PWM will give you more liner dimming and you can ‘safely’ over drive the LEDs for more output. I’ve thought about doing something like this for nice liner dimming of LED back lit dashes. But it’s going to be some time before I get anything on paper much less built, maybe end of winter but probably not. If I get anything done I will be posting the results. If I do this for dashes it will take a 0V to 12V input for dimming. You’ll need to add a frequency to voltage converter. If you know you’re way around a transistor and soldering iron I could point you in the right way. If not, good luck finding something pre-built to do this. And if you find something post it back here so I can take a look see at it. Good luck...

 

i think it would be cool for the tach to control other lights too. Maybe underbody lights or interior lights. Then again, it might not be cool. I had interior mood lights before the fast and the furious movie though. That movie kind of wrecked my thoughts of puting any more lights in. I'd hate to mistaken for a civic from a mile away.

 

Buy this:
http://cgi.ebay.com/ebaymotors/Sunpr...spagenameZWDVW

Cut all the traces to each LED on that board and have them all run to a single LED. Use resistors accordingly.

 

My LO3 puts out a constant voltage at a varying frequency which (due to duty cycle) ends up looking like a varying voltage. Give it a shot as a quick test...just don't overload it or you'll have a weak ignition!

At work here, one of our PCBs used to tap LEDs in to the Tx & RX signals of an RS-232 interface at line levels. The LEDs were VERY dim until we redisgned and had the Tx & RX lines drive transistors which drove the LEDs. Now, they are very bright and seem to get brighter with RS-232 port speed (i.e.: moving data @ 9600bps appears more dim than at 115200bps)

 

well, i changed my setup of the way i am going to do my dash and it turns out i probably will just use colored bulbs like already in the dash. The advantage is that dimmin led's seems to be kind of a problem but dimming a standard bulb is done every day by people. Is their a way to do this? If they can make a needle move on a tach, why cant they make that turning action into spinning a variable resistor?

 

There is no difference between powering an LED and powering a bulb.

And the whole variable resistor ISN'T going to happen. You'd be better off finding a circuit that has a variable output voltage instead.

Are you looking to build one or just buy one. Becuase there isn't anything you can do short of building one as far as I've seen.

 

Dont mean to steal the thread just need a bit of info on similar note!!Im just wondering what size resistor to hook to an LED??Im thinking of putting a LED in my dash and hooking it to unused knock sensor on the block in my 89 so i can see if there is any detonation going on at boost.

Also thinking of building a custom A/F ratio meter.I have plenty of IC's and LED's.

Also id like to try the third brake light LED thing.I just need to know what size resistor if anyone knows!!Thanks

 

There's a thread here regarding the DIY knock sensor indicator, I don't know the voltage so I don't know what to reccomend. Prbably around 1K should be fine but that's just a random number.

If you're making a custom AFR meter, just don't.
http://www.aces.edu/~gparmer/efi/temp/wb/guide.html

Everything you need to know. There are units out there for $200 that look better and the end result of building your own is like $40 cheaper. I considered it but unless I find that sensor for cheap I'm not gonna bother. If you're not going to install a wideband oxygen sensor then it doesn't matter since your gauge won't do anything.

And for the LED taillight thing, give some more details and I'm sure I can help you.

 

I belieeeeve the knock sensor outputs a constant +10V when no detonation is occuring and drops to 0V when it's detected. You could use a transistor to simultaneously buffer and invert the signal to turn an LED on only during knock. Plus, you know the voltage to the LED will be +12V with the transistor. Not a bad $1 idea!

P.S. The current-limiting resistor is based upon the operating voltage of the LED and the voltage feeding it.

 

So the knock sensor makes a perfect trigger for a 555 timer eh? Make the duration of the LED a tiny bit longer for practical purposes.

 

Ahh...and here we go...I knew someone on here had to have typed it all out before:

https://www.thirdgen.org/techbb2/sho...hreadid=171217

Check it out if you want to understand the resistor question.

 

Gonna make a new thread for my questions.Sorry for the hyjack.