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Old 08-09-2011, 04:56 AM   #95
Joined: Nov 2010
Location: Melbourne, Australia
Oddometer: 5
Using a coil pickup

Guys greetings again - has anyone thought to use a coil (primary side) as a VSS pulse pickup? I've been told by BMW that the K1200S (sorry don't have a GS!) despite having the same GPS connector on it as the GS's (with TTA on Pin 2), it doesn't work. I've measured it and could only read about 11mV at 100km/h. I doubt this is enough to reliably trigger the VSS

I propose using a primary ignition coil lead which pulses with firing frequency. As the K1200S has coil on plugs the primary lead is low voltage suitable (I assume pulsed 14.5VDC).
We need to know how many pulses per mile (PPM) or kilometre this method will provide. Here's the calculations:
• At 100km/h you cover 27.8 metres/second 

• At 100km/h, in top gear, the K1200S engine is running at about 3500rpm 

• The ignition coil fire frequency will be half that at 1750rpm for a four stroke engine which divided by 60 is 29.2 pulses/sec 

• So in 1 metre, the bike would have 29.2/27.8 = 1.05 pulses. 

• So pulses per mile (PPM) would be = 1.05*1612 .14 = 1691 PPM 

• Pulses per km (PPK) = 1050 PPK (for the metric lovers out there)
• So we set the Rostra switches 3-6 into the OFF position which is a 2000 PPM setting. The Rostra setting needs to above the max PPM calculated so this looks fine.

Would be interested in knowing if anyone has done this before successfully, or found issues with this approach.

Cheers Kendrick

kpavey screwed with this post 08-09-2011 at 05:05 AM
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