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small relay to turn on the buzzer; you may need a driver circuit, see the Eggtimer web site
(
www.EggtimerRocketry.com
) for details. Similarly you can also use the nice little sounders sold
by Adept Rocketry, they make a very distinct sound that’s hard to miss even with other
background noise present.
ALED/BLED - Deployment Channel LEDs
ALED/BLED are designed to provide a visual indicator of deployment channel power and
igniter continuity. This lets you know immediately after connecting the igniter and powering up
the channel if something isn’t right. They use relatively little current, so leaving them on isn’t
likely to be a significant drain on your deployment battery.
The ALED/BLED outputs are current-limited with 820 ohm resistors, a 9v battery on the outputs
will source about 9ma of current to the LEDs. This is more than enough to brightly light up a
high-brightness T-1 sized LED. Note that these outputs are polarized, they are /-, so
you need to make sure that you have these connected properly; the long lead of the LEDs goes to
the + output. If you’re using an LED that’s pre-wired in a holder, connect the red wire to the “+”
pad and the black wire to the “-“ pad.
A Note on Wiring
The Eggtimer is designed to have the wires directly soldered to the board. This allows you to
choose whatever method of terminating the connections you want: barrier strips, solder directly
to the switches, etc. We’ve found that simply wire-wrapping the igniters to a “pigtail” wire
soldered to the board works very well for smaller rockets. By soldering the pigtails to the board
rather than having screw terminal blocks, you eliminate the possibility that the wire may work
loose from the terminal in flight.
We recommend using #22-#26 gauge wire for wiring to the Eggtimer board, we like to use the
#24 gauge stranded wire that’s found in Cat-5 network cables. It’s cheap, easy to find, and just
the right size. It’s also twisted together in nice solid-striped pairs, so it’s easy to tell the “+”
from the “-“ wire. You can also use solid wire, but solid wire is harder to work with and has a
tendency to break after being bent a few times. These breaks can be a pain to find, because they
are typically inside the insulator jacket where you can’t see them.
If you use stranded wire, you
MUST
TIN THE WIRES BEFORE SOLDERING TO THE
BOARD. This is to prevent stray “whiskers” of wire strands from coming loose and bridging
pads, or breaking off and landing on the board in some random place. We’ve seen the results of
this happening, it’s not pretty, and they can be very hard to find if the lodge underneath the
processor chip or in some other hidden spot on the board.