Andy:
I am so interested in finding out how easy it would be to detect the plunger position on the SC0323L part that I sent an email to the company to see if they would send me one or two sample parts!!

It seems to me that since the microcontroller would have a driver output pin on the coil already to release the "set" plunger, that it would be a piece of cake to modulate the coil at some frequency in the KHz range via a software algorithm in the microcontroller. This frequency would be chosen so that the solenoid woukld not change state due to the application of the drive frequency. Then by monotoring either the RMS current draw or some other characteristic of the coil it should be possible to note if the plunger is seated in the coil or not!!

Note: I agree that the idea that mahmood gave about the circuit breaker may be a good one conceptually....but I wonder about the cost....I used a remote trip type of circuit breaker at one time quite a few years ago and the thing had a price tag over $35 USD back then (over 15 years ago). Clearly you could use the circuit breaker as a true breaker, ie note the switch open / closed position and then "trip" or by shorting your 12 volt power supply through the thing. Besides the cost factor the current spike needed to trip the breaker may lead to nasty ground spikes in the other parts of the vending machine. Even a low amperage breaker such as 1 A unit such as a W58 series thermal breaker may require 1.5 A or more to reliably trip. This unit as shown here...

http://www.pandbrelays.com/datasheet...W58_DS.pdf

... will cost twice what the solenoid does in OEM quantities and is only rated at 1000 cycles.

Michael Karas