4 image::telemetrum-v2.0-th.jpg[width=400]
7 image::telemetrum-v1.1-thside.jpg[width=400]
9 TeleMetrum is a 1 inch by 2¾ inch circuit board. It was designed to
10 fit inside coupler for 29mm air-frame tubing, but using it in a tube that
11 small in diameter may require some creativity in mounting and wiring
12 to succeed! The presence of an accelerometer means TeleMetrum should
13 be aligned along the flight axis of the airframe, and by default the ¼
14 wave UHF wire antenna should be on the nose-cone end of the board. The
15 antenna wire is about 7 inches long, and wiring for a power switch and
16 the e-matches for apogee and main ejection charges depart from the
17 fin can end of the board, meaning an ideal “simple” avionics
18 bay for TeleMetrum should have at least 10 inches of interior length.
20 There are two generations of the TeleMetrum design. The
21 major changes after v1 generation are:
23 * uBlox GPS chip certified for altitude records
25 * Higher power radio (40mW vs 10mW)
29 Otherwise, they're the same size, with mounting holes and
30 screw terminals in the same position.
32 === TeleMetrum Screw Terminals
34 TeleMetrum has six screw terminals on the end of the board
35 opposite the telemetry antenna. Two are for the power
36 switch, and two each for the apogee and main igniter
37 circuits. Using the picture above and starting from the top,
38 the terminals are as follows:
40 .TeleMetrum Screw Terminals
41 [options="header",grid="all",cols="2,3,10"]
43 |Terminal #|Terminal Name|Description
44 |1 |Switch Output |Switch connection to flight computer
45 |2 |Switch Input |Switch connection to positive battery terminal
46 |3 |Main +++ |Main pyro channel common connection to battery +++
47 |4 |Main - |Main pyro channel connection to pyro circuit
48 |5 |Apogee +++ |Apogee pyro channel common connection to battery +++
49 |6 |Apogee - |Apogee pyro channel connection to pyro circuit
52 === Using a Separate Pyro Battery with TeleMetrum
54 As described above, using an external pyro battery involves
55 connecting the negative battery terminal to the flight
56 computer ground, connecting the positive battery terminal to
57 one of the igniter leads and connecting the other igniter
58 lead to the per-channel pyro circuit connection.
60 To connect the negative battery terminal to the TeleMetrum
61 ground, insert a small piece of wire, 24 to 28 gauge
62 stranded, into the GND hole just above the screw terminal
63 strip and solder it in place.
65 Connecting the switched positive battery terminal to the pyro
66 charges must be done separate from TeleMetrum, by soldering
67 them together or using some other connector. Note that you
68 must include a switch in the positive lead from the pyro
71 The other lead from each pyro charge is then inserted into
72 the appropriate per-pyro channel screw terminal (terminal 4
73 for the Main charge, terminal 6 for the Apogee charge).
75 === Using an Active Switch with TeleMetrum
77 As explained above, an external active switch requires three
78 connections, one to the positive battery terminal, one to
79 the flight computer positive input and one to ground.
82 The positive battery terminal is available on screw terminal
83 2, the positive flight computer input is on terminal 1. To
84 hook a lead to ground, solder a piece of wire, 24 to 28
85 gauge stranded, to the GND hole just above terminal 1.