project idea: led tachometer

Greetings, I am new to netduino and have a couple quick questions about its capabilities, and a project idea to let you guys in on. But to explain the situation, I have a bit of background info... I am about to finish up converting my car to use a Megasquirt EFI fuel injection/ignition system. Unfortunately, my cars tachometer will no longer operate as it recieves a 12v pulse from the stock ignition coil. However, the Megaquirt ECU can emit a 12v (or 5v) pulseing signal that can either be a pulse per revolution or a pulse for 2 revolutions. So i am planning to run a pulsing 12v signal to the stock tachometer to get it to work, but also would like to take that same 12v signal and run it to a Netduino and allow it to light consecutive LEDs with increasing rpm. But the Netduino seems overkill for just this so I thought some other features would be good as well, but more on that later. I thought possibly the Netduino could convert that pulsing signal to a varying voltage (1v-5v) signal that can be sent to an LED bar driver. So I want the LEDs (say 12-20) to light up in a bar until just before the rev limit, then at the rev limit, have ALL the LEDs flash on and off rapidly. I can also send a separate "shift light" signal from the ECU, so I can use that input to trigger the flashing. Any advice about what ICs to use or how to wire it, or coding tips would be greatly appreciated But I thought since all this could be done with cheap ICs, I thought I should include more features... So the first I thought would be good is a gear selection display. I would basically need a single didgit LCD or MFD screen than can display R, N, 1, 2, 3, 4, & 5. but i thought for this, I would need to do alot of clever switch mounting on my gear lever arms. (3 arms, so 6 switches) But I thought the switch mounting would be the hardest part, the rest would be ALOT of code. (all switches off = N, then as each switch gets depressed, its a different gear) And the next thing that would be great is a lap timer. this would be another LCD or the like screen that just runs a stopwatch. now the easiest would just have it controlled by a button, but it would be incredible to have a GPS controlled timer. This means you press a button and that will set the GPS start/stop location, and everytime that location is passed, the time is displayed for a full second, while a new timer starts, and saving times would be great, even if it was just saving the fastest time. I thought installing a photocell to adjust brightness of the LEDs and screens would be great too Now I think that all these things would be possible running off a single Netduino, just will require alot of wiring, and intricate design. But any advice or insights some more experienced people could give me would be a huge plus, and really get me started on my way.. Or any other 'motorsport' related gadgets you think of that I can include would be welcomed as well, though I dont want to make it too cluttered.. TIA for the help

I would basically need a single didgit LCD or MFD screen than can display R, N, 1, 2, 3, 4, & 5. but i thought for this, I would need to do alot of clever switch mounting on my gear lever arms. (3 arms, so 6 switches)

I was thinking about this too a while ago (but changed car and postponed the project): I planned to use either optical or magnetic sensors mounted around the gear lever in a way that the lever interrupts the light beam (*) or alters its direction (small piece of a reflective tape), or switches a magnetic switch (a reed switch or a Hall-effect sensor) with several small magnets glued on it. I did not want to use mechanical switches and for me the priority was a 'non-invasive' mount that could be easily removed (i.e. a PCB with hole in the center where the lever goes).

(*) The basic operation is depicted in the attached image. For my gearbox, detection of all 7 states could be done with 4 light sensors (perhaps less, using some clever tricks like diagonals etc.), the truth table is as follows (the output value '1' means light detected, the actual logic level may vary depending on the circuit, i.e. transistor switch output is inverted):

 X0 | X1 | Y0 | Y1 | Gear
----+----+----+----+------
  1 |  1 |  1 |  1 |   N
  0 |  1 |  1 |  0 |   1
  0 |  1 |  0 |  1 |   2
  1 |  1 |  1 |  0 |   3
  1 |  1 |  0 |  1 |   4
  1 |  0 |  1 |  0 |   5
  1 |  0 |  0 |  1 |   R

The Netduino's definitely up to the job. I'd suggest you start with just the tacho and just add more as you get used to it. You're right that it could be described as overkill using a Netduino as a counter, but that's the best way to learn your way around.

Some initial suggestions off the top of my head:

• Use an optoisolator for the pulses coming into the Netduino.
• If the pulses are to quick or the Netduino's timing inaccurate, you could use a counter IC to track the pulses and read the value from that.
• Don't bother converting the tacho reading to an analogue signal to drive the LED bar - just light up the LEDs you need directly depending on the value.
• The GPS idea would work, but might be annoying if you can't get that initial GPS fix when you need to!

Also, there are some very nice displays around that you could use. I hope you weren't thinking or ruining your car with some 7-segment red LED display from the 70s!

I hope you weren't thinking or ruining your car with some 7-segment red LED display from the 70s!

IMHO a big (~10 cm) 7-segment single-digit red LED display is a must for the gear indicator

Thanks for the helpful replies. I like the gear-select idea, I was looking at some short-range IR proximity sensors, just on the backside of the shift arms, but worry abouut signal reliability. As for the GPS, i was thinking I would try to spend a little more for a better quality module, and just have a button to set the start/stop, with an led that lets you know when the satellites are acquired. The speedometer would be very simple if I had the gear selection. It already has an rpm plus I could program in my gear ratios, diff ratio, and tire size. Or use the GPS... The time display will be a nice LCD but the gear select display will be maybe not a 7-segment but maybe a 13-segment display. This car is an 85, so I try to keep some of the stuff period correct. I will definitely document this build because I know alot of people who will want something similar. Overall, I plan to spend no more than $100 but that may go up depending on the GPS. Either way, finding something similar would cost me $700+, have less options, and still have wiring and configuring to do. I'm not new to electrical wiring, or even component soldering, and I have done a tiny bit of C coding.. But I am no EE and have never really done my own micro-controller project before, so I plan to get on here for help/advice. I will start small with just the LED bargraph, but since mounting will be difficult and I want it to look nice, I will wait till I have all the components before putting it all in my case so I dont have to go back in and make room. Look for more info soon...

Well to keep the display looking "fresh" I was actually thinking of using multi-color LEDs for my tach. Have them green for the first few lights, then at a certain point, they ALL turn yellow as RPMs increas, then when they reach a certain point, they ALL turn red. The issue with this is, the only multi-color LEDs I can find are RGB. Does anyone have any suggestions for LEDs that can be Green, Yellow, AND Red? would that make driving the LEDs too complicated to bother with it? I think it would look much neater. My Netduino should arrive any day now. I also ordered a 16-segment (2cm X 3cm) for my gear display, I am about to order a GPS shield with flash SD data-logging (Can that also be used to log my lap times??) and a Serial Enabled LCD Backpack, for my 20 X 4 LCD screen (or should I get the I2C??). I went a little bigger than originally planned for more "...flexability" hehehe. So any LED suggestions? Or suggestions for photo-optic sensors that I should get to use the above explained gear detection method? Thanks guys. Oh and I've started working on faceplate and case mockups, based on listed measurements, so I should be able to upload some pics of my progress pretty shortly after the Netduino arrives.

Does anyone have any suggestions for LEDs that can be Green, Yellow, AND Red?

You can use RGB LED, it will produce yellow when red and green are on simultaneously (or switching fast enough; see additive color mixing). There are also red/green LEDs available, but RGB LED driven by PWM has much greater flexibility of mixing different colors (including white).

Or suggestions for photo-optic sensors that I should get to use the above explained gear detection method?

Any phototransistor which is sensitive to the light produced by the LED should work fine, there are numerous parts for IR range (840 - 980 nm) and for example BPW40 is sensitive to red light (85% relative sensitivity for ~650 nm). For this particular case (short distance, no ambient noise), the component selection is not critical.

Any phototransistor which is sensitive to the light produced by the LED should work fine, there are numerous parts for IR range (840 - 980 nm) and for example BPW40 is sensitive to red light (85% relative sensitivity for ~650 nm).

That's right.
Bear in mind that *ANY* semiconductor junction exposed to the light will act as a photo-detector. So, even a normal led is a photo-detector. However the sensivity of a led is much fewer than a specialized component.
Cheers

thanks for the input guys. I guess I'll get a handful of RGB LEDs and I've been looking at some different IR sensors, and I guess if I use a narrow-angle light and sensor, it should be fine. And luckily, when I get my getrag transmission, I'll just have a tiny bit of code editing to compensate for the dog-leg first gear. I hope I dont run out of pins on my Netduino (hence using the I2C) but I'll pick up a few shift-registers or the like just in case (again, making the code more complex, but more options = more appeal) Look for some progress updates soon, hopefully I can get the main items done without too much complication. I have a forum full of people interested in these, so I'm working on a way to have a "position display" so others who make a unit like this can Copy-&-Paste my code for when they drive on the same track. Since it will have a lap timer and counter, it could do a position display, if it could detect other Netduino systems..

Sorry to dig up an old post, but your project interests me also, and I was wondering if you've made any progress? I’m working on a similar problem, but I’m not as concerned about the display, but instead the actual gathering of the data. I think wiring into the existing tachometer sensor would be great, but I’m not sure how accurate it is on older cars. I also want crank position information so I can do engine timing related events. Anyway, I’ve just added this topic in case it might help with some of your plans... http://forums.netdui...ino-tachometer/