Technical > Ignition

Tacho options

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Sprocket:
Whats the score with tacho signal.

Currently the tacho is connected to the negative of the single coil/ dizzy set up. I will be using DIS. The later Minis had a different tacho and looks like it is connected to the DIS coil, I am led to believe that this MPi tacho reads twice that of a standard one if used on a coil/ dizzy set up.

How do I go about getting a signal for the tacho and would it be easier to locate an MPi tacho and just connect it to the DIS coil. I have heard of pull up diodes, but dont quite understand this at the minuit. I also heard about setting up another FET for the tach output.

Oh and another thing, the coil pack has a four way connector, is there a common wiring configuration for the majoriy of coils?

dnb:
You'll need to make an inductive pullup to drive the tacho if it is expecting a high voltage signal.  There's instructions on my WIKI page - will dig them out.

Sprocket:
Any further on with this info? ;D

dnb:
For the second time today...

I intended to draw up a circuit diagram for this, but never completed it.  Maybe I should talk about getting a PCB done so it can be sold as a tacho converter in the webshop?  Just another thing to do...

The P259 can handle the (appr 0.4A peak, 0.15A effective) current of the inductive pullup, but you need a 600V 1A .. 2A diode (ER2J or ES2J is fine) to protect the P259 output. An additional 200..400V bidirectional transient suppressor provides clamping.

ER2J cathode (marked with a stripe) connected to P259 output
ER2J anode connected to inductor
inductor connected to 22 Ohm 2W resistor
22 Ohm resistor connected to 1A fuse
1A fuse connected to +12V
bidirectional transient suppressor diode
one end to resistor (the leg close to +12V)
other end to inductor (where the ER2J diode anode is also connected)

Sprocket:
Ive opted to go the route of the MPi tacho. I just need to get hold of one. It simplifies things, i just dont understand the pull up thing, not that i wont, i just havent looked at it. The MPi tach connects directly to one of the coils in the DIS pack, simple as. The loom has been wired acordingly.

Off out down to the local 'ye ha' Mini spares center to see if they got one :-\

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