I am attempting to fire 8 solenoids from a 16F628 and am inexperienced
at playing with solenoids.

The setup:
One 16F628 connected to an optoisolator (necessary?) then to 8 power
MOSFETs (with necessary resistors in tow).  8 mini 12V push solenoids
(with flyback diodes) on the high side of the MOSFETs.

Upon a trigger, I want to fire the solenoids (sometimes all 8 at once)
and hold for 2 seconds or so.

I am having somewhat success using PWM to control the initial current
then drop it down once the coil is saturated to avoid burnout.
Schematic:
http://www.damonhamm.com/other/pic_solenoid_schematic1_pwm.gif
(Initial tests do not utilize the #1 RC 'decoupling' circuit.)

But, the MOSFET (1.5A? in a TO-220 case) heats up to be quite hot to
the touch, which I wouldn't consider viable.  Using 5V at the MOSFET
gate (full on or PWM at 100%) doesn't produce enough current to fire
the solenoid, while using 12V with PWM at 20% for 100ms, then at %1 to
hold for 2s, still causes everything to heat up much too much after
several cycles.  I am still surprised that a duty cycle of 1:255 (~1%)
still provides too much current!  Is there something wrong with my
setup or are the MOSFETs just too wimpy?  I have some 6Watt DIP
MOSFETs on the way to test out.

Has anyone had any experience with solenoids that they can offer?  Any
resources, circuit critique, and component suggestions would be
greatly appreciated!

I have looked at DRV101T solenoid drivers (PWM), but would rather save
$100 and use my solution.  My multimeter always reads 0 current
flowing when I attempt to see what the solenoid is using (can one not
read current in series with inducors or is my MM fried? - had a 120V
short with it years ago but everything else works fine).

Thanks!

- Damon

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