MOSFETS and Solenoids

[mackrackit]

Thanks for pointing that out. Theoretically, if the board is completely isolated like the attached schematic I will be immune to electrical noise like markedwards is talking about or am I just minimizing it?

If noise is found to be the problem and it is really bad then a grounded metal enclosure might also help. Think Faraday Cage...

[markedwards]

I didn't see any large capacitor for the battery + connection to ground.
With high frequency noise there is a significant impeadance between the battery and your device.
A scope will show you high frequency noise that your aquisition system
will likely average (filter) out. The aquisition system is similar to a DMM with a slower response. It will not show high frequency spikes or voltage dips.
Ignition and similar electrical noise can be conducted and re-radiated
inside the metal enclosure.

What is the solenoid's dc current draw?

[Tobias]

There is a capacitor on the chassis. Its sold by the ignition company. Its pretty big, about half the size of your fist.

The solenoids draw 26 amps per stage. Some cars will have four stages. The fourth stage requires 14 amps.

Our data acq system only samples 50 times a second on the logger voltage. I did hook up my scope to VIN with the cap disconnected and its pretty scary. The cap really helped alot.