On Sun, 27 Dec 2009 23:54:59 +0000, Ian Bell wrote:

snip

The PIC is an 8 pin DIL, costs a dollar and allows me to light a couple
of LEDs to show the HT state, handle the cable interlock and drive the
relay. It needs no external clock components and there's even a spare IO
line I could use for a push button emergency off switch.

snip


I tried something similar to this - using a PIC - a while ago, but never
actually put it into practice. The idea was to drive 2 relays. One
switched the HT on and the other shorted out a series resistor in the HT
line after a few seconds to give a soft-on characteristic. A single
button was used to control everything and a 2-colour LED for Off/Standby/
On indication (provisionally). Software was written in GCBASIC just
because it was a quick-n-dirty way to do it! The eventual idea was to
also monitor the cathode current of the output valve & shut down with an
error indication if it got too high. I never got to that bit because I
couldn't arrange a grounded DC supply for the PIC. The PIC is still
floating around somewhere... I like PICs... :-)

You must *never* depend on software for safety interlocks by the way.
It's very bad design.

--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
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