Eggtimer Rocketry Eggtimer User Manual page 25

K Airstart Min Velocity <0-700 by 50>
This allows you to set a minimum velocity that the rocket must have attained in order for CHB to
fire in airstart mode. If the velocity of the rocket is less than this value when the airstart timers
expire, CHB will not fire the airstart igniter. This prevents the second stage from igniting if the
rocket turns horizontal, because the resulting altitude-derived velocity will be significantly lower
than the actual velocity in that case, and you don't want your second stage to be ignited if the
rocket isn't pointing upwards.
If your rocket's velocity appears to be lower than it actually is due to mach transition rather than
being in a horizontal position, and you have this value set too high, the airstart igniter will fire
when the rocket comes out of mach, assuming that the velocity of your rocket is above this
value. See the section on airstarts for further elaboration and suggested values.
L Telemetry <0=Off, 1=On>
When set to "1", flight time and altitude samples are sent through the serial port in real-time
during flights. Data streaming begins as soon as the pre-launch sampling begins, and continues
until the flight ends. Even if the memory runs out, the telemetry data will continue to stream
after landing is detected, it just won't be saved to flight memory. If you're using some kind of
RF telemetry package, this insures that you're going to get a continuous data stream that you can
use to help find your rocket on the ground. We've all wandered around deserts, cow pastures, or
farm furrows for a few hours looking for a wayward rocket, so you can see the value in this!
Only two wires are required to send data to an external device, the GND and the TX lines. TX is
a TTL-compatible output (low < .8v, high > 2.4v) NOT an RS-232 output (low > 3v, high < -3v).
Data is streamed at 19,200 baud, 8 bits, one stop bit, no parity, no handshake, so you will need to
make sure that your radio device is configured for that rate. The Eggtimer's output signal is
compatible with many common telemetry transponders such as the X-Bee and 3DR radios.
Note that many radio telemetry devices require a FCC Amateur Radio Novice license, so check
before you purchase anything. If you want to get into telemetry, you should probably go ahead
and get a Novice license anyway, you'll need the knowledge to get your telemetry system
working and it's pretty cheap... the exam fee is only $14 and the study guide is about $30.
Obviously, telemetry is a detailed subject in itself, so we will not cover it any further here.
O Comments
The Comments field is a 42-character free-form text field that you can use to identify you flight,
enter the data, rocket name, motor, etc. We recommend that you change it for every flight to
make it easier to identify the flights when you go to download them later. If you choose a pre-
programmed flight profile, it will be set to "Default Flight <n>", where <n> is the flight profile
number from 1 to 8.
- 25 -