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== Using Altus Metrum Hardware
Here are general instructions for hooking up an Altus Metrum
flight computer. Instructions specific to each model will be
found in the section devoted to that model below.
=== Wiring and Electrical Interference
To prevent electrical interference from affecting the
operation of the flight computer, it's important to always
twist pairs of wires connected to the board. Twist the switch
leads, the pyro leads and the battery leads. This reduces
interference through a mechanism called common mode rejection.
=== Hooking Up Lithium Polymer Batteries
All Altus Metrum flight computers have a two pin JST PH
series connector to connect up a single-cell Lithium Polymer
cell (3.7V nominal). You can purchase matching batteries
from the Altus Metrum store, or other vendors, or you can
make your own. Pin 1 of the connector is positive, pin 2 is
negative. Spark Fun sells a cable with the connector
attached, which they call a
link:https://www.sparkfun.com/products/9914[JST Jumper 2 Wire Assembly]
Many RC vendors also sell lithium polymer batteries with
this same connector. All that we have found use the opposite
polarity, and if you use them that way, you will damage or
destroy the flight computer.
=== Hooking Up Pyro Charges
Altus Metrum flight computers always have two screws for
each pyro charge. This means you shouldn't need to put two
wires into a screw terminal or connect leads from pyro
charges together externally.
On the flight computer, one lead from each charge is hooked
to the positive battery terminal through the power switch.
The other lead is connected through the pyro circuit, which
is connected to the negative battery terminal when the pyro
circuit is fired.
=== Hooking Up a Power Switch
Altus Metrum flight computers need an external power switch
to turn them on. This disconnects both the computer and the
pyro charges from the battery, preventing the charges from
firing when in the Off position. The switch is in-line with
the positive battery terminal.
=== Using an External Active Switch Circuit
You can use an active switch circuit, such as the
Featherweight Magnetic Switch, with any Altus Metrum
flight computer. These require three connections, one to
the battery, one to the positive power input on the flight
computer and one to ground. Find instructions on how to
hook these up for each flight computer below. The follow
the instructions that come with your active switch to
connect it up.
=== Using a Separate Pyro Battery
As mentioned above in the section on hooking up pyro
charges, one lead for each of the pyro charges is connected
through the power switch directly to the positive battery
terminal. The other lead is connected to the pyro circuit,
which connects it to the negative battery terminal when the
pyro circuit is fired. The pyro circuit on all of the flight
computers is designed to handle up to 16V.
To use a separate pyro battery, connect the negative pyro
battery terminal to the flight computer ground terminal,
the positive battery terminal to the igniter and the other
igniter lead to the negative pyro terminal on the flight
computer. When the pyro channel fires, it will complete the
circuit between the negative pyro terminal and the ground
terminal, firing the igniter. Specific instructions on how
to hook this up will be found in each section below.
=== Using a Different Kind of Battery
EasyMini and TeleMini v2 are designed to use either a
lithium polymer battery or any other battery producing
between 4 and 12 volts, such as a rectangular 9V
battery. TeleMega, EasyMega and TeleMetrum are not designed for this,
and must only be powered by a lithium polymer battery. Find
instructions on how to use other batteries in the EasyMini
and TeleMini sections below.
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