[App_rpt-users] Slight mod to DMK GPIO driver circuit when used for a fan controller
Bryan D. Boyle
bdboyle at bdboyle.com
Wed Feb 1 09:07:30 EST 2012
In hacking (thanks, Kyle) through getting both the script working (hey,
had to modify it for my own install, which is a good thing...:)) and
addressing the proper node/dongle number...and getting the parts to
build the circuit (at Radio Shack, believe it or not...) as shown at the
DMK site so I could actually drive my cooling fans (with 3 repeaters, a
100w amp, and batwing spectra transmitter that gets Real Toasty even at
12w out, the amount of constant noise is a bit much, even in the
basement...not to mention the electricity consumption), it's all up and
However, in talking with Scott KB2EAR, he brought up the issue of the
possibility (not remote..) of the controller or a dongle hanging or
going brain dead in between the time that the radio keys up and the fan
controller script turns on the relay...with the possibility that the
radio would key (along with the amp...) but the fans would never come up.
So...belt and suspenders time. I have an extra box of shalco
thermoswitches...NO contacts, close at 115c, reopen at 95c or
thereabouts. Since the relay (I like electromechanical stuff, ok?
Nothing like the sound of contactors closing all around the shack when
you press one button...brings me back to the days of running BIG
transmitters and the plate contactor closing when you pressed 'PLATE ON'
and saw the plate voltage meter swing to 18KV @ 2.6A) that's being
driven by the DMK circuit is actually controlling the B+ to the fan
string...putting one of the thermo switches across the armature and NO
contact of the relay...well, if the computer hangs, or the relay fails,
and the transmitter and amps are up...when they get warm enough, the
secondary mechanical (rather than logical) circuit takes over and STILL
turns the fan on. I'd rather fail, if that's the scenario, with cooling
flow across the heat sinks than not.
Obviously, this implies that the logical circuit is driven from the same
power supply as the fans (mine are...) to eliminate that issue.
Anyway...wired that up as an addition to the relay circuit; actually,
it's just a pair of wires coming back from the shalco and paralleled
across the leads from the relay.
Just throwing that out there for y'all's consideration, if you're
building the circuit from DMK to do something like this.
(Still have to mount the DMK circuit on perfboard in a small project box
and clean up the wiring...right now, it's just hanging by its wires in
front of the repeater shelving unit (plastic...one of those Sears
Final cost, by the by, of the DMK circuit, using bits and pieces from
the Shack, was under $10 USD, btw. And the biggest cost was the big
piece of perfboard (which I cut down, so I have lots extra to use for
other projects) and the small DPDT relay. Bought the 10-pack of
transistors, 10-pack of diodes, and couple sleeves of the 4.7K
resistors, so, have some extras to build other interfaces...
In this world, you must be oh so smart or oh so pleasant.
Well, for years I was smart. I recommend pleasant.
You may quote me.
Sent from my MacBook Pro.
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