The Pyro Panel

So, there I was, setting up flash pots and gerbs for Tech. Unlimited's
SpecTECHular '95. We didn't have a control panel at the time, so we rented one.
I was appalled to find out that the rental bill was over $100. I was sure I
could make my own panel for that price. It ended up being a bit more expensive
than that, but it was well worth the cost and effort.

THE MISSION: to build a full-featured pyrotechnics
control panel that, after a year, would be less expensive than renting similar
equipment. The panel must have remote-control capabilities, so that operation is
possible from the control booth of our local auditorium, about 100 feet from the
stage. The system must be modular so that setup is neat and versitile.

THE PLAN: Run 8-pin DIN cable from the panel to
"breakout boxes" where electric matches can be hooked into the system. AC
switches or other effects can be hooked in parallel to the DIN cable as well.
The panel will be able to control 14 independent circuts.

14 CIRCUTS WITH 8 WIRES? That's right.In order to make
the wiring more compact, each conductor controls two independent circuts: one
circut is triggered by a positive current, the other by a negative current. With
one ground wire, there are seven signal wires for a total of fourteen
independent circuts.

CONTROL LAYOUT: The front panel is fairly impressive,
IMHO. For each of the 14 circuts, there is an LED (it lights green if there's a
charge connected, red if the charge is armed), an 'arm' switch, and a 'fire'
button. (My version actually also had a 'master fire' button that would set off
all the armed circuts simultaneously, but I haven't taken the time to document
that here. Figure out how to do it yourself, if you want to.) I tell ya, it sure
was a task to solder all those components together.

MATERIALS:

Most of the parts I ordered through MCM Electronics, so I'll give their part
numbers if applicable. This is not a full list ready to be taken to your local
wholesaler, it is only intended to give you and idea of what to include in your
own list.

power supply (110 VAC - 50 VAC)

key power switch

'power on' indicator lamp

case

8-pin DIN connectors

8 conductor telephone wire

8-pin inline DIN plugs

for each circut:

two-color LED with appropriate resistor to work at 50V

'arm' switch

'fire' button

high-power diodes

for each breakout box:

case

8-pin DIN connectors

terminals as necessary

a high-power diode for each circut

I used a 50 volt power supply because the higher voltage is more efficient
over long cable runs. Two 110V-25V transformers (MCM # 28-0015) did the trick
for me. The power cord (MCM # 23-150) was helpful in getting power to the unit.
I used a key switch (MCM # 26-070) for safety purposes, of course, and also
because it looks cool to have a pack of keys hanging out of the panel. Finally,
as far as power goes, I got a pair of neons lamps (from Radio Shack, neat ones
with red plastic housings) so that it is obvious when the panel is on.

The case I used was 1/2" plywood with an angled top. The controls were
mounted on a plexiglass panel. Why plexiglass? Well, it's clear: I was able to
sandwich a piece of vellum in between two sheets of plexiglass so that I could
use my printer (on the vellum before I put it together) to neatly label the
controls. I used vellum instead of normal paper so that I could backlight the
whole thing. On the back of the box I put three DIN jacks (for flexibility in
connecting stuff). All the DIN jacks are the same, you can include as many or as
few as you want.

The cable was 8-pin telephone wire (MCM # 36-625), mainly because it's cheap.
It works well with the 8-pin DIN connectors (MCM # 27-675). It's somewhat of a
pain to be soldering all those 26 AWG stranded wires onto the contacts of the
DIN plugs, but it sure beats spending $15 per 10 feet of premanufactured
computer keyboard cable. The cable is about 15 cents a foot from MCM. I made a
variety of lengths of cables so that I can hook up breakout boxes and whatnot
however I want for a particular show.

For each circut on the panel, I needed the 2-color LED (MCM # 25-280), an
'arm' switch (MCM # 26-580), and a 'fire' button (MCM # 26-705). The 'arm'
switch needs to be DPDT (a fairly hairy wiring is required with the 2-color LED,
needing to reverse the polarity to change the color). The 'fire' button is a
momentary SPST: make sure it's red. I'll explain the wiring later.

On to the remote boxes, the ones that actually do the pyro work: for
simplicity's sake and just to get the system working faster, I made only two
breakout boxes, each with 8 sets of terminals for electric matches. I simply
slapped a 16-terminal barrier strip (MCM # 28-725) onto the side of a black
plastic Radio Shack project box and stuck some wires in it. Later I made a
little device that will switch a 110V lamp or what have you, utilizing a relay.
Possible additions in the future include self-contained flash pots or gerb
holders, strobe triggers, audio synthesis doohickeys, you name it. Each box or
whatever that I've got has two DIN jacks on it, in parallel, so they can be
daisy-chained together.

WIRING THE PANEL: The basic idea is that the circuts
come in pairs. The odd numbered circuts are positive, the even are negative.
Let's look at circuts 1 and 2, for now: You'll have a positively oriented diode
in the input (50VAC) power to the circut. In the 'unarmed' position of the
switch, the current will be going through the LED, resistor, and the first
conductor in the DIN outputs. It'll come back in through the ground conductor
and return to the transformer. With the switch in the 'armed' position, the
current will be flowing the opposite direction through the LED and resistor (to
make it red instead of green) and then to the DIN output. Furthermore, the
'fire' switch will be introduced into the circut so that, when pressed, it'll
short out the LED and resistor. Pretty straightforward, but a picture sure
wouldn't hurt. Hopefully this'll explain it for you.

Make sure that you get the two-color LED oriented so that it's green when the
'fire' button is disabled and red when it is enabled. Also note that you have to
reverse the polarity on it for the other circut. Polarity is especially
important in this project because of the compression on the signal wires.

WIRING THE BREAKOUT BOXES: This part is pretty simple. I
used a black Radio Shack project box for mine. You'll want to put at least two
DIN jacks on the box so you can daisy-chain the boxes together. Just wire the
two in parallel. Then, decide which circuts you want to use in the box. Use a
high-power diode to filter out the unwanted circut on a particular conductor and
hook it up to one of the screw terminals (or whatever) where your electric match
is going to be. Then, just hook the other terminal to the ground conductor.

Hopefully there's enough info here to get you started with your own
pyrotechnics control panel. The modularity of this design allows for incredible
creativity as far as what you can hook up to it. Please let me know if you use
any of the information here. If you want more info, I'm happy to give it to you.
Just send me some mail.
[email-masked]