Confused with TACHINPUT

[spiderman]

Hello all,

I am using MS3 on v3.00 board. I am simply following the assembly instructions from the link:
http://www.megamanual.com/ms2/V3assemble.htm

I am planning to use Hall Effect sensor to read engine crankshaft hence I have built the circuitry with opto-isolator as mentioned in the page above. I have tested the input circuitry with JimStim without any problems, ie. I am able to read RPM with Tuner Studio.

However when I read from the MS3(base)/V3.0 Hardware Guide from the link:
http://www.msextra.com/doc/pdf/MS3baseV ... re-1.4.pdf
I realized that document mentions to wire TACHSELECT to VRIN for both in sections 5.2.3 and 5.2.4 (ie. meaning that one needs to build VR circuitry)

At this point I am a bit confused, could you please explain me what is going on?

Sincerely.

[DaveEFI]

Don't use the MegaManual if using Extra Code. Use the ones linked to at the top of this page. They were written for Extra Code.

[spiderman]

Ok I understand. I shouldn't use MegaManual. This becomes clear for me after reading the link:
http://megasquirt.info/educational/

Nevertheless what is your comments on tach input? It works just perfect, and as far as my understanding on schematics (schematics from msextra) optoin circuitry seems more convenient for a Hall Effect sensor as a tach input. As I have mentioned before, RPM signal reading is just working with opto circuitry with JimStim.

Sincerely.

[kjones6039]

FWIW...... I absolutely recommend using the VR circuit!

Been there, done that!!!

Ken

[billr]

Umm... if it is working fine, leave it as-is!

It can also work fine using the VR input, but no need to bother changing it now. Of course, if you ever "re-purpose" this MS to use (or temporarily try out) on a different install, you may wish you had finished the board and had VR or some adjustment for Hall threshold available.

PS: note that I have to take the OP's word that it really is working fine.

[DaveEFI]

Ok I understand. I shouldn't use MegaManual. This becomes clear for me after reading the link:
http://megasquirt.info/educational/

Nevertheless what is your comments on tach input? It works just perfect, and as far as my understanding on schematics (schematics from msextra) optoin circuitry seems more convenient for a Hall Effect sensor as a tach input. As I have mentioned before, RPM signal reading is just working with opto circuitry with JimStim.

Sincerely.

It may work just fine. The problem *might* arise if using a hall effect with a multi-tooth wheel. The opto input may not be able to keep up with the number of pulses at very high revs.

[Dennis930]

It may work fine on the JimStim, but once reading the actual toothed wheel at high RPM's there could be hickups depending on the frequency response of the sensor.

[spiderman]

Thank you so much all, I have decided to leave it as it is for now. I am going to use VR circuit if there are problems with optocoupler's response in real system.

[kjones6039]

Thank you so much all, I have decided to leave it as it is for now. I am going to use VR circuit if there are problems with optocoupler's response in real system.

Excellent choice, IMHO!

Ken

[eeklaca]

It may work fine on the JimStim, but once reading the actual toothed wheel at high RPM's there could be hickups depending on the frequency response of the sensor.

I use a bmw e46 330i with factory hall sensor and 60-2 wheel. Its working perfectly with the opto isolator circuit, only need to replace the C11 10n capacitor to a smaller, I use 330 pf.

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