On May 27, 2006, at 7:10 AM, Russell McMahon wrote:

> Nobody seems to have solved your 'latch on' conundrum.

Thanks for asking, I'm still very curious about this.

> You didn't provide quite enough information for us to be sure what  
> you are doing.
>
> Can you provide a full circuit of the relevant portion OR describe it
> fully.

I have a 1K resistor on the base, and have tried switching using the  
PIC, and by hand -- touch wire to 5V, touch wire to Gnd.

I have a surplus 50V 5A linear power supply (built like tank,  
delightful 60Hz hum generator). +V is connected to solenoid, other  
side of solenoid to the collector, emitter connected to Gnd.

There is a snubber diode connecting the emitter back to the  
collector.  Which as I look at it is not literally in parallel with  
the solenoid, but the book I got this from claims that this is  
equivalent.

> When you turn it off, how do you do it - do you ground the resistor  
> input via  PIC pin or  float the driving pin.

Tried with PIC, floating, and connecting to Gnd.

> If you ground the input to the 1K resistor when the large solenoid is
> on, does it till stay on?

yes

darren
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