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Message started by 360k+ on 05/17/12 at 19:07:34

Title: Rotor pulses?
Post by 360k+ on 05/17/12 at 19:07:34

Has anyone ever probed the rotor pulses to see what their analog characteristics are? I'm curious because it would be easy to design an LED readout tach for a few dollars that could be mounted near the speedo. If not, I'll test the pulses and post results here (I have a scope).

Title: Re: Rotor pulses?
Post by Serowbot on 05/17/12 at 19:16:43

I don't even know what a rotor pulse is...
...but, I'd sure like to see one, if you're willing to explain what I'm lookin' at... :-?...

Neat!.. Sumpin' new!... That'll be great... ;)...

Title: Re: Rotor pulses?
Post by justin_o_guy2 on 05/17/12 at 19:40:41

Scope it out & let us know,, then splain how the tach works,, I survived electronics in the Air Force,,dang near 40 years ago, so Im sharp as a bowlin ball,, but I still understand some of it,

Title: Re: Rotor pulses?
Post by Dj12midnit on 05/17/12 at 19:41:35

I thought rotor pulsing was caused by getting a hot rotor wet?

Title: Re: Rotor pulses?
Post by thumperclone on 05/17/12 at 21:38:56

why not pick up a signal from the ignition coil like most tachs do..
my lcd tach pick up is induced from the plug wire..

Title: Re: Rotor pulses?
Post by 360k+ on 05/18/12 at 08:46:10

4C504D55485D4A5B5457565D380 wrote:

why not pick up a signal from the ignition coil like most tachs do..
my lcd tach pick up is induced from the plug wire..

The rotor is the counterpart of the stator in the alternator, and constitutes the spinning component. Rotor pulses are generated by a special magnet on the rotor passing by a stationery coil (sensor). This pulse ultimately determines ignition timing, and there is one rotor pulse per engine revolution.

There are a few of places on the engine where rev pulses can be detected with advantages and disadvantages to each. One problem with ignition coils is they have a nasty side effect of producing high voltage spikes which could be detrimental to a microprocessor. However, the spikes can be mitigated by taking some precautions such as the use of zener diodes. While I'm looking at the rotor pulses I will also scope the coil's primary pulse to determine it's suitability.

Title: Re: Rotor pulses?
Post by teabowl13 on 05/18/12 at 12:23:22

WHOA!! Gettin' Nerdy up in this Hizzie.... ;D

(sorry.... been a long week, I couldn't help myself. All in good fun. ENJOY!)

Title: Re: Rotor pulses?
Post by prechermike on 05/18/12 at 12:28:33

575142490905030209300 wrote:

[quote author=4C504D55485D4A5B5457565D380 link=1337306855/0#4 date=1337315936]why not pick up a signal from the ignition coil like most tachs do..
my lcd tach pick up is induced from the plug wire..

Title: Re: Rotor pulses?
Post by CaptialThumper on 05/18/12 at 17:20:51

My EE spider sense is tingling. I can't wait to see the scope plot!

Title: Re: Rotor pulses?
Post by 360k+ on 05/18/12 at 18:23:55

OK, I've got the scope data, but lemme ask... as a forum noob with 5 or 6 total posts is it going to allow me to post my jpgs? Admins or moderators?

Title: Re: Rotor pulses?
Post by 360k+ on 05/18/12 at 19:35:41

OK, I think I have pics figured out now. Warning, technical discussion follows...

The first 3 pics show the rotor pulses at 3 different engine revs. The last shows the coil signal, and why I am trying not to use it. The rotor pulses show the scope across the coil wires with no ground reference at all (i.e., floating). The coil pic shows the connection between the ignitor output transistor and the coil primary as referenced to ground. Don't worry too much about the rotor pulse voltages as that can be reshaped to anything I want, but do pay attention to the wave shape and period (timing).

http://i1266.photobucket.com/albums/jj534/gary95329/Timing/1153RPM.jpg

http://i1266.photobucket.com/albums/jj534/gary95329/Timing/2307RPM.jpg

http://i1266.photobucket.com/albums/jj534/gary95329/Timing/3750RPM.jpg

http://i1266.photobucket.com/albums/jj534/gary95329/Timing/CoilPrim.jpg

Title: Re: Rotor pulses?
Post by CaptialThumper on 05/18/12 at 19:43:18

Wow, the coil really rings.

What digital hardware are you planning on using?

Title: Re: Rotor pulses?
Post by 360k+ on 05/18/12 at 20:18:44

Ahhh, I am detecting another engineer pod here. Ignition coils actually tend to act like flybacks, thus producing a duration period for the spark. I thot I had another picture that showed more than one coil pulse at speed, but I guess my camera decided not to take the pic (remember the days when WE HUMANS decided? LOL)

Anyway, the rotor coil has a nice consistent wave form as I suspected. I was planning on rectifying the pulse, disregarding the negative side (magnet leaving coil proximity), then buffering and clipping to a square wave and feeding to an MPU.

I'm not sure about the output yet, and wanted to get some feedback here on the forum. One idea I had was to use a 2 digit LED display showing the 1000's and 100's of RPM, discarding the 10's and ones. If that much resolution is not needed, a bar graph LED array might even work, and would give you resolution to the nearest 1000 RPM. The display should probably be something that can be grasped in a glance without having to think. Hopefully, some other ideas will surface.

BTW, I am a retired engineer (Apple - 20 years).

Title: Re: Rotor pulses?
Post by thumperclone on 05/18/12 at 23:23:04

bar graph led tachs are on the market, pricey boogers tho..
can you do what you are trying for under $35 retail.the plug wire fed lcd display tachs can be had for around $35.
think northern tool has one..
mine says pit posse on it, had it on thumperclone(chinese ct70) b4 i bought my ls

Title: Re: Rotor pulses?
Post by ratz on 05/19/12 at 07:54:35

6563707B3B3731303B020 wrote:

And here's a schematic! (Sorry,I couldn't resist!) I'll see if I still have my scope data from a previous excursion into the unknown.

Title: Re: Rotor pulses?
Post by 360k+ on 05/19/12 at 08:48:28

Hey ratz, very interesting schematic. Looks darned versatile too and easily adapted to other projects I had in mind. 8-)

Actually, after a quick googling, the tach project looks like it's already a well beaten mule. One thing that might be interesting tho is a 4 digit display of 2 digits for RPM and 2 digits for cyl head temp (rounded to the nearest 100 and 10 respectively).

Title: Re: Rotor pulses?
Post by ratz on 05/19/12 at 08:54:29

Main problem I've had with that schematic is getting the electric eel to settle down. I've found that Thevenin's Thereom solves this by confusing the eel into submission. ;)
I do like the idea of adding cylinder temp!

Title: Re: Rotor pulses?
Post by CaptialThumper on 05/19/12 at 19:59:50

Apple retiree? Shouldn't you be using a retina display? :D

Title: Re: Rotor pulses?
Post by Savage_Rob on 05/22/12 at 14:47:57

If you're looking for a tach reference, the black/yellow wire on the coil is working perfectly for my new KOSO tach.

Title: Re: Rotor pulses?
Post by mpescatori on 05/23/12 at 04:43:16

5452414A0A0600010A330 wrote:

Hey ratz, very interesting schematic. Looks darned versatile too and easily adapted to other projects I had in mind. 8-)

Nice but it's flawed, a bit like Spangsen's Theorem of Tungsten:

- you can't have a 120ohm resistor coming out of the cloverleaf junction box unless you specify the thermic reactance of the variable resistance at the other end;

- the South Pole of the compass is too weak to do any good to the blender towards which it is pointing, there is insufficient Coriolis effect on the core windings;

- similarly, you can't open&close the switch fast enough unless the electric eel is connected to a blond bombshell surfer from SoCal - provided her name is Ethel...

- the scarab beetles in the glass jar will never glow like fireflies if you use a transient resistor with two cathodes in parallel;

- the bat and the mouse cannot operate properly in series, you could clog the 240AC generator with a posicharged negatron (read that as = static charged fur ball) - have you considered in parallel with a cheeze-whiz stub ?

- there are too many triangles to balance the stars :-/

- The arena has two cathodes going in but no anode going out ? You always go out from the anode side... 8-)

- The moral rectifier you picture is actually a DOD surplus rectified moralist, it is evident from the anode-retentive siamesed one-way cathode straps... ::)

- Can the 500AC generator produce sufficient heat to bake the PI (=greek cake) unless the vibrator is of Klystron brand.

- The pretzel-resistor which regulater the Tear Collector is excessive and you may risk tearing it - may I suggest a figure-8 resistor which will dissipate heat more efficiently while maintaining relative humidity closer to the intrinsic values of a nuance-triggered hygrometer;

- The flux-capacitator is on backwards, I can see the stitches on the Professor's suspenders

- IEEE rule 87.485.333-A1 prohibuits the use of Holy Water as a ground/mass device; you could, in theory, protect your ground/mass from accidental reverse-charge shock (=short circuit) via a Ghost thermistor, but I see you only use two pins off the 666 timer? Are those odd or even numbered pins, and are they sequential or alternate?

Anyway, I appreciate your ingenuity and your dedication.

May I present you with an appropriate prize...

http://i1188.photobucket.com/albums/z412/FiveToolTool/DDDD.png

8-) 8-) 8-)

Title: Re: Rotor pulses?
Post by ratz on 05/24/12 at 06:40:06

Well,thank you,I've never gotten a major award before! ;)
And it's good to know I'm not the only one with too much time on his hands! (Or in your case,WAY too much time on their hands!)

Title: Re: Rotor pulses?
Post by mpescatori on 05/25/12 at 01:28:35

OK, but...

...what about the blond bombshell surfer from SoCal ?
Will it be OK if her name isn't Ethel ?

:D

Title: Re: Rotor pulses?
Post by Savage_Rob on 05/25/12 at 08:01:47

504356584C445043454C220 wrote:

Well,thank you,I've never gotten a major award before! ;)
And it's good to know I'm not the only one with too much time on his hands! (Or in your case,WAY too much time on their hands!)

I just pictured Darren McGavin exclaiming "It's a major award!".

http://img.photobucket.com/albums/v642/shakespeares_sister/shakes2/leglamp.png