Eggtimer Rocketry Eggtimer User Manual page 11

Reset Switch (RST)
When shorted, the Reset terminals put the Eggtimer "on hold", i.e. resets it so that it does
nothing. When it is in reset mode, it draws very little power from the battery, < 2 ma. All
outputs are held low, so this is the "safe" mode when multiple deployment systems are used;
they cannot be triggered while the Eggtimer is reset. This can be used to put the Eggtimer in low
power mode while it's sitting on the pad for a long time, and can be released shortly before
launch to help save battery life.
When the reset switch is opened, the Eggtimer begins the startup sequence. You will hear a
continuous "beep-beep" sound, the programming screen is displayed for 30 seconds, and the
flight sequence begins if no keys are pressed within this time or the button is not held down to
select a pre-programmed flight profile. After approximately 20 more seconds, the Eggtimer
begins taking altitude readings and recording, and chirps until launch to let you know that it's
ready for flight.
If you use a multiple deployment system, we STRONGLY recommend that you have some sort
of external switch or shorting plug to hold the Eggtimer in reset mode until shortly before
launch. A lot of people have had good results with 2.5mm earphone jacks, you simply wire each
lug to the RST terminals then you short the leads on the plug together. Hang a "Remove Before
Flight" ribbon on the end of the plug, and you're ready to go; simply pull the plug out when
you're ready to launch to start the Eggtimer flight sequence.
You can also use the same rotary switch listed above in the Power Switch section, they're a little
pricey at $5 each but they work very well. For larger rockets where you have the room and are
spending a lot of money anyway, it's definitely the way to go.
The Reset terminals are also used to update the firmware on the Eggtimer, see the instructions on
the Eggtimer web site ( www.eggtimerrocketry.com ) for details.
Breakwire (BW)
A "breakwire" is used to definitively indicate that the rocket has lifted off. This technique is
used on "real" rockets, and works very well for arming multiple deployment rockets as well,
particularly for airstarts. Basically, when a rocket lifts off a wire that is connected between the
rocket and the pad breaks an electrical connection, and that event triggers a liftoff sequence.
In the case of the Eggtimer, the breakwire is optionally used to arm Channel B in airstart mode.
This provides an additional level of safety to prevent accidental airstart ignition; for the igniter to
fire, the breakwire must be tripped AND the rocket must have reached the LDA altitude AND
the Burn Timer/Airstart Timer must have expired after LDA. This virtually eliminates any
possibility of the second stage igniting on the pad. As we have mentioned before, you should
shunt the igniter or remove power to the igniter until just prior to arming the Eggtimer and
launch.
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