$1.49 LM2917 IC does tachometer, MFI Speed Switch, rev limiter, or shift light ...
 

For all of you electronic experimenter types out there ...

I was looking at the data for this IC normally used and recommended for tachometers ... and, lo and behold, it has other capabilities that come to mind for 911 applications ... only a few additional components are needed to have a complete, working 'black box' ...

Here is the site to download the datasheet and application note AN-162:

http://www.national.com/pf/LM/LM2917.html

Different versions are available for use with points [single-ended input] or magnetic reluctor inputs [SC and Turbo distributors] ... so if you have a non-functioning tach or speedo that is already apart, here is an easy way to revive it with some modern IC technology and just a bit of fabrication on a universal breadboard -- if you aren't inclined to make a circuit board from scratch! There is also a LM2907 version, but the LM2917 version is preferred because of a built-in Zener to regulate Voltage to the circuit.

Just a few 911 applications:

1. Tach repair -- replace old VDO board needing unobtanium parts ...

2. MFI Speed Switch/RPM Transducer/Speed Relay ... replace an ancient Bosch board that has seen better days ... at very low cost!!!

3. Adjustable rev-limiter/shift lamp ...

4. Speedometer repair -- for electronic versions, only -- easy calibration for new/different tire sizes ...

Sounds very interesting Warren, since my speedometer has been being flaky lately. I'm not very electronically inclined, but not a total clown either. Will you be ordering some of these and perhaps performing a procedure or two you might care to document?

ianc

Hmm. . . . all sorts of possibilities here. By converting ground pulses from the tach into a voltage, you could drive a meter movement, also known as the tach needle! By converting the same pulse to a voltage, as soon as it was exceeded, this could trigger a transistor, hooked to a relay to actuate the stop solenoid. . . .

Pretty cool Warren. Thanks.

Someone (I'm not an EE) figure the circuit and create directions to use a common low cost digital speedo with this...and a relay (voltage or frequency based) that will close a switch...like a 964 decklid on an earlier car for automatic raising of the spoiler...or something else that might be too graphic for the general Pelican Board :) ... something that makes the ear wheels spin faster :D

Thank again for the help with tranny information these last couple of days, Warren. And for the rest of the five years of advice I have cherished. It'd be cool if you'd consider performing these upgrades and enhancements and repairs for a fee. Let the speedo shops replace odo gears and repaint gauge faces. You repair the CD boxes, the MFI speed switches and the other stuff I don't understand like what you said above. I'd like a switchable CHT gauge. And a voltmeter, but even I know that's easy.

I second that.....If you can build a box that I can tap into my speedsensor & trigger my soon to be new 964 spoiler on my 84 911, I would buy one....providing i dont have to mortgage the house to do so....

So if you build one, they (me at least) will buy.......

Let me know, Thanks
Chris
chgrec@yahoo.com

Warren, Hi there. Funny you should write about this chip for this use. I have a current lunchtime project going of just such a shift lamp for my GT4 911. We are using exactly this chip; built on a breadboard with potentiometers for range and span adjust. Found the trigger points to be ratiometric to the input voltage, so we added a 10volt regulator circuit. Some protection diodes on the lines and.......
It works great on the bench with a function generator. I am using a small LED array for the light itself. The scope indicated system voltage (13v) of 3 pulses per rev on the tach signal line. When I start the engine, the light "flickers" a few times, but that is it.
Any ideas? I'd really like to get it going. Peter

Peter,

What kind of distributor signal are you using, i.e., points or electronic conversion ... or SC/Turbo magnetic reluctor signal???

Which exact chip designation [LM2917N-8 or LM2917N] are you using?

Also, do you have a sketchof the current breadboarded circuit you can post?

This is good stuff guys, i am going to lurk here and see how it turns out.
Not sure if I can add much, but I will if I see an opportunity to do so...;-)

Hi Warren, I am trying to use the circuit on a 2.8 RSR clone. It has a bone stock ignition system i.e. points in the distributor with Bosch CD box. The chip we used is the LM2907N. I guess we missed the fact that the other has the zener built in, so we added this externally. I am using the tach line as my trigger (Black/Purple if memory serves). I will clean up the beer napkin sketch so I can post it. I leave for Mosport tomorrow, so I will get it posted as soon as possible (it may not be until next week). The circuit is based off the drawing #26 in the National Semiconductor book (2-95). By the way, I am the mechanical Porsche guy and my colleague here at work is the EE.....Thus we! Anyone into this stuff, please feel free to write directly. Peter

Look into a Freescale 68c908qt4 8 bit micro controller and you could go nutz with these for auto hobby applications.

Built in A/D, timer, FLASH, Oscillator, Reset and the C compiler/emulator is free from Metroworks. I have played with several of these for applications like logging temerature, counting pulses etc and I have the cost of 5 parts invested (less than $1 each).

No idea what you guys are talking about (zener, ...) but I'd like to come up with a shift light for my electromotive crankfired / autometer setup that is not the real huge flashlight type that autometer makes.

Can you help ???

Great info! Anybody get it working yet? I just replaced my '71 E tach today that has been woking intermittently with a spare T tach... works fine except for the wrong rev-limit redline. Would like to fix the old one if possible. Evren. ps: Warren thank you for the CDI help!.. :)

Guys, Sorry for the delays. I'm still working on posting a copy of the schematic. Peter

Greetings, Don't know if anyone is still into this thread, but I finally got drawings of our circuitry. I have it in .jpg and a couple of other formats. Can anyone help me on how to attach or upload to the thread? Otherwise I can private email. The drawing includes the connector, light, and car side as well as the main circuitry. As I had said earlier, it worked on the bench, but only flickers on cranking in the car. I feel we are close, but maybe some E.E. can tell me where I went wrong.
Peter

Peter,

Click the 'post reply' button lower right.

Click 'Click here to upload a photo'. Browse to where your .jpg is.

That is all.

ianc

I,m sure many people think this is very intereresting ! but i had nothing to add to this thread so i diden,t reply. Please keep the info coming this is a great thread :)


Cheers,

yep... still here, lurking

yes, very interested.... would appreciate it if you could email schemetic.

Hi Folks, Well it's taken me forever, but I finally have it. Here is a link to the schematic.

http://innoves.com/pmaehling/20050817_ShiftLight.pdf

The left 2/3 is the actual shift light circuitry; on the right is a voltage regulator and the 4 pin connector showing the integration into the vehicle. I can try to explain bits of it as needed. Remember this took a while because I am the Porsche mechanical guy and my friend here at work is the Electrical Engineer. He quickly made the drawing, so I hope he got it correct. We used potentiometers so I could adjust the RPM trigger point and a second to adjust the hysterisis for turning the lamp back off.

Now the bad news. It works on the bench, but only flickers on cranking when in the car. I am running a totally stock ignition system in my 72 RSR clone. Any thoughts are welcome. Feel free to steal as desired!

The trigger is the tach line, which is 3 pulses per revolution at system voltage (12.5 or so).