Electronic Experts and F1 Fans

[richardhaggarty]

I have done a search for an F1 Style LED Tach for a couple of days now and come up with not much. Someone who follows F1 auto racing may have seen one on the F1 car steering wheels.

What I am looking for is an LED bar gauge that represents engine speed (RPM). Ideally it would have 15-30 LEDs and look something like this:

.......Green.............Yellow..................R ed........................Color
OOOOOOOOOOOOOOOOOOOOOOOOOOOOO..............LEDs
0k.................5k...................10k....... ...........15k..............RPM


I figured the 12V lead to one of the ignition coils could work, but how do I pull that signal to the guage with out stealing voltage from the coil? It would pulse once (or maybe twice?) for each rotation of the engine.

Any Ideas?

[daveo]

I don't fit either criteria...however the coils are fed 12V+ constantly, the primary side ground is broken to discharge(spark) the secondary, so if you hook your LEDs up to a fused 12V+ lead and use the neg.- lead from the ignition to the coil, you wouldn't be using the coils' power, just sharing it's ground

[Anonymous]

What I am looking for is an LED bar gauge that represents engine speed (RPM).

I'm no electronics expert (that is a bit of an understatement... ), but I have done some research on making my own tach similar to this concept. You need something that will keep time and count pulses, then do the math to figure the RPM and display it. Not really that hard as PLC stuff goes. Something like the OOPic would be perfect and it is very simple to work with:

http://www.oopic.com/

I was thinking of picking up a signal from an inductive pickup mounted on one of the plug wires for mine. It seems easier than picking up the coil signal and does not affect the ignition operation at all.

Other than that, the closest thing I have seen to what you want is an electronic shift light. But they only flash at the preset RPM, so you don't know where you are until it lights up. If you find one or a DIY kit, let me know as I am still interested in one for a future project.


Mark

[Anonymous]

Take the signal from the pulsed side of the coil. If you buffer it with a comparator (use hysterysis) then the load will not affect the coil operation.

The output of the comparator will then be a digital logic signal pulsing at 1/2 the RPM of the motor (assuming a 4 cylinder) that you can manipulate to your hearts desire.

The circuitry shouldn't be too complex. I would be willing to assist you if you need help. The hardest part, IMHO, would be finding the LED that you want to use. After that, it's just a matter of conditioning the pulse from the coil to give you the appropriate input to the LED.

Package it nicely and you have what you want.

[DMPLATT]

You have my full attention on this project. Keep us informed. My stock Tach Sucks and I'm interested in an alternative. This one sounds interesting.
Earl has a digital that is a possibility too.

Thanks. This is a cool idea.

[2Fast4U]

I plan on getting this http://www.veypor.com/ when I get some extra money. Its not the exact thing you want but close.

[Guy]

Just a thought:
The alternator output is directly proportional to the engine speed.
Rather than use digital or logic circuitry to drive the leds, you could drive them using zener diodes to set up the threshold voltages.
One for 500rpm, 750rpm, 1000rpm, 1250rpm, 1500rpm and so on.

[Guy]

Having thought some more about this, I realise my idea is flawed. Alternator output IS directly proportional to engine speed AT A GIVEN LOAD. As the load is constantly changing it might be a little inaccurate. Oh well, I'm sure someone on here has it all figured out. I'd be interested in building one myself.

[Anonymous]

Having thought some more about this, I realise my idea is flawed. Alternator output IS directly proportional to engine speed AT A GIVEN LOAD. As the load is constantly changing it might be a little inaccurate. Oh well, I'm sure someone on here has it all figured out. I'd be interested in building one myself.

It would be a bear to calibrate. Even if you got it correct for one bike, the next would have a different voltage output level. You also have to calibrate to take into account the tolerances of the components. Then as you say, the level would change if the lights went on. Too many variables.

Digital logic is the way to go. Believe me on this one. It's much simpler, easy in fact, and there is no calibration.

[earlfor]

You were right the first time. :-) Alternator output is proportional to engine rpm. Load is not a factor. Stator output (for example) at 4000 rpm is the same, regardless of whether the stator is hooked up, lights are on, off etc.

Earl.

Having thought some more about this, I realise my idea is flawed. Alternator output IS directly proportional to engine speed AT A GIVEN LOAD. As the load is constantly changing it might be a little inaccurate. Oh well, I'm sure someone on here has it all figured out. I'd be interested in building one myself.

[Anonymous]

I re-read you post and found that I misread it. I scanned it too fast.

The methodology that I briefly outlined would work, however, let me throw something out there and see if anyone likes it.

Instead of using a series of led's, why not use an led digit display? I'm not a big one for digital displays, but it may look pretty trick. You could have the bar bleow it, or even just one led set for redline - or two led's yellow at 400rpm befor redline and a red one for redline.

Just an idea anyway. Here is an example of what I'm talking about.

http://www.para.com.tw/pdf/E-Display/E35-CA505X.pdf

Those are only 1/2" characters. Bigger can be found I'm sure.

[Anonymous]

National Instruments used to make an LED driver that would be perfect for this application. I think it was the 3914 and 3916, one was a logarythmic response and one was linear. They drove either 8 or 16 leds depending if you cascaded them and cost about 3 bucks each.

I've also seen them for sale. There was one with LEDS embedded in a rubber strip that you glued to your windscreen. The one I saw broke down after about a month but was only 70 bucks shipped.

Steve

[richardhaggarty]

The National Semiconductor "LM3914 is a monolithic integrated circuit that senses analog voltage levels and drives 10 LEDs, providing a linear analog display."

The rest of the data sheet can be found here:

http://www.national.com/pf/LM/LM3914.html

I think thats the one, (of course, I will be accepting Swanny's offer to assist with the circuit, this is all quite new to me).

Swanny, how about two or three of these next to one another:

http://www.ledtronics.com/ds/CBG1500/

Looks like LedTronics has plenty of other options too:

http://www.led.net/datasheets/PCB_picture_index/PCB_picIndex.htm

I like the idea of about 30 or so LEDs in a line, maybe for a total length of around 4-5 inches, for the visual effect of the bar screaming across the display matching the howl of the exhaust. I admit though that the digit display is more precise; having both I think is an excellent idea.

However, since my plan is to scrap my whole stock panel I would like to use the digit display for my oil temp and fuel gauge; make a completely digital minimalist display.

Could I make the array from individual LEDs?

Honestly, I stole the idea straight off of the F1. Shhh!

[Anonymous]

The tach would need a frequency to voltage converter.

For the rest the 3914 would be all that's required. You could get a few figure 8 type LED displays and setup enough chips to drive each display. There would be 10 inputs for a 0-9 LED display and there are 10 outputs for the chip. If you had 3 chips in a row you could convert the voltage into a 3 digit display. Do you sort of get my idea? My only concern is that I thought that National SEMICONDUCTOR (not Instruments, that is a data acquisition company ) stopped making them in an easily soldered form.

I don't want anybody to abuse a component manufacturer, but they will usually send out a couple free samples if you tell them you are part of a company that wants to research the use of their product in a large production run.

Steve

[Anonymous]

oh yeah, the 3914 can also be used along with an O2 sensor to tune your engine. If you set 14.7:1's voltage in the centre of the display you can use the display to see if you are rich or lean. Too bad we don't have 4 into 4s for easy interpretation.

Circuit diagrams are on the web.

Steve