The rev counter issue

jano · Post by **jano** » Sun Mar 07, 2010 12:21 pm

I have a SMITH RVC rev counter that I'm trying to get working with megajolt.
I have built the suggested circut with the zeners and even purchased the prebuild thingy from triggerwheels, but I can't get it to work.

When the engine is at idle, the rev counter shows about 1500 rpm, but when increesing the revs the needle drops to zero like a hammer and stays there.

The homemade version goes to about 2500 rpm before the needle is pulled to zero, the one one from triggerwheels drops instantly when accelerating.

What am I doing wrong?

/jano

B@man · Post by **B@man** » Sun Mar 07, 2010 2:33 pm

Don't start me on rev counter woes.... I just found out mines current driven not pulse !

Anyway this is about your problem rather than mine - Have you tried the circuit with the Zener removed (just the two diodes)

NITROPIXIE · Post by **NITROPIXIE** » Sun Mar 07, 2010 7:02 pm

Try Pin 11 of the EDIS module. This is the CTO or Clear Tacho Output. Sometimes there is not a pin 11, in this case you can also try pin 2 which is the IDM. This is a diaognostic output which emits a 500rpm signal when the EDIS module has power applied and then an a signal representing rpm when the engine is started. This could be used to confirm the EDIS has 12v when the ignition is switched on.

Gilesy998 · Post by **Gilesy998** » Sun Mar 07, 2010 10:26 pm

Have you tried the simplified tach diode circuit? Basically touch your tach trigger wire on the INPUT of the Zener diode, eliminating it from the circuit. I know of people that have had good success with this after getting exactly the problem you describe regarding the needle hitting a wall and dropping to 0.

jano · Post by **jano** » Mon Mar 08, 2010 12:14 pm

I'll try to kill the Zener.

also I found this one http://www.autosportlabs.org/viewtopic. ... r&start=30 looks very much like my scenario and suggests to wire the rev counter directly to the PIP signal.

/jano

alhbln · Post by **alhbln** » Tue Mar 09, 2010 10:30 pm

B@man wrote:Don't start me on rev counter woes.... I just found out mines current driven not pulse !

This might help:
www.dinoplex.org/tachoconversion/

B@man · Post by **B@man** » Wed Mar 10, 2010 7:47 pm

alhbln wrote:
B@man wrote:Don't start me on rev counter woes.... I just found out mines current driven not pulse !
This might help:
www.dinoplex.org/tachoconversion/

Thanks I found that,

I took it apart and found that it was a Stewart Warner instrument that had a proper iron cored transformer on the coil feed to convert current pules to voltage pulses. So I cut the track after the transformer and added a zener + 1K resistor and injected the pulses into the tach and it works perfectly, just tested it at work with a square wave generator !

Saved £75 !