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== TeleMetrum
.TeleMetrum v2 Board
image::telemetrum-v2.0-th.jpg[width="5.5in"]
.TeleMetrum v1 Board
image::telemetrum-v1.1-thside.jpg[width="5.5in"]
TeleMetrum is a 1 inch by 2¾ inch circuit board. It was designed to
fit inside coupler for 29mm air-frame tubing, but using it in a tube that
small in diameter may require some creativity in mounting and wiring
to succeed! The presence of an accelerometer means TeleMetrum should
be aligned along the flight axis of the airframe, and by default the ¼
wave UHF wire antenna should be on the nose-cone end of the board. The
antenna wire is about 7 inches long, and wiring for a power switch and
the e-matches for apogee and main ejection charges depart from the
fin can end of the board, meaning an ideal “simple” avionics
bay for TeleMetrum should have at least 10 inches of interior length.
There are two generations of the TeleMetrum design. The
major changes in the v2 generation are:
* uBlox GPS chip certified for altitude records
* Higher power radio (40mW vs 10mW)
* APRS support
Otherwise, they're the same size, with mounting holes and
screw terminals in the same position.
=== TeleMetrum Screw Terminals
TeleMetrum has six screw terminals on the end of the board
opposite the telemetry antenna. Two are for the power
switch, and two each for the apogee and main igniter
circuits. Using the picture above and starting from the top,
the terminals are as follows:
.TeleMetrum Screw Terminals
[options="header",grid="all",cols="2,3,10"]
|=========================
|Terminal #|Terminal Name|Description
|1 |Switch Output |Switch connection to flight computer
|2 |Switch Input |Switch connection to positive battery terminal
|3 |Main + |Main pyro channel common connection to battery +
|4 |Main - |Main pyro channel connection to pyro circuit
|5 |Apogee + |Apogee pyro channel common connection to battery +
|6 |Apogee - |Apogee pyro channel connection to pyro circuit
|========================
=== Using a Separate Pyro Battery with TeleMetrum
As described above, using an external pyro battery involves
connecting the negative battery terminal to the flight
computer ground, connecting the positive battery terminal to
one of the igniter leads and connecting the other igniter
lead to the per-channel pyro circuit connection.
To connect the negative battery terminal to the TeleMetrum
ground, insert a small piece of wire, 24 to 28 gauge
stranded, into the GND hole just above the screw terminal
strip and solder it in place.
Connecting the positive battery terminal to the pyro
charges must be done separate from TeleMetrum, by soldering
them together or using some other connector.
The other lead from each pyro charge is then inserted into
the appropriate per-pyro channel screw terminal (terminal 4 for the
Main charge, terminal 6 for the Apogee charge).
=== Using an Active Switch with TeleMetrum
As explained above, an external active switch requires three
connections, one to the positive battery terminal, one to
the flight computer positive input and one to ground.
The positive battery terminal is available on screw terminal
2, the positive flight computer input is on terminal 1. To
hook a lead to ground, solder a piece of wire, 24 to 28
gauge stranded, to the GND hole just above terminal 1.
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