On Wed, 28 Jul 1999 22:39:43 +0200 Louis <Louis@SNAFU.DE> writes:
>I'm not that good in electronics, so i just ask a simple question
>here.
>I have made a device to operate glow-plugs of model-airplanes.
>Basically, it is just PWM-generation.
>Well, the problem is, that i cant make the PIC "see" if the glow-plug
>is
>actually connected.
>It seems to be the old "current-sensing" problem, but i dont want to
>put
>any extra components into this.
>This is the circuit so far:
>
>---     12V
>P I      I
>I I      ---->1
>C I      ---->2  to glow-plug
>  I      I
>  I      I
>  I      I
>  I     D
>  I----G   N-Channel Enhancement-Mode FET, Logic Level
>  I     S
>  I      I
>---      I
>        GND
>
>
>The resistance of the glow plug is around 2-3 ohms.
>Any suggestions ?
>

        How about a 10 K resistor across the FET, then a 47K or so
resistor from the drain of the FET to a PIC input.  With the FET off, the
drain should go high.  If the glow plug is absent, the 10K will pull it
low.

Harold


Harold Hallikainen
harold@hallikainen.com
Hallikainen & Friends, Inc.
See the FCC Rules at http://hallikainen.com/FccRules and comments filed
in LPFM proceeding at http://hallikainen.com/lpfm

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