doc: add a brief note about TeleBT appearing inert until paired

[fw/altos] / doc / motortest-installation.inc

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+== Installation
+
+       EasyMotor needs to be rigidly attached in the airframe, and the
+       long axis of the circuit board needs to be aligned with the axis
+       of flight.  By default, the round beeper on the board should be
+       "up" towards the nose cone, and the screw terminal strips should
+       be "down" towards the fins and motor nozzle end of the rocket.
+
+       === Power Switch and Battery
+
+               In addition to the circuit board itself, EasyMotor needs 
+               a power switch and battery to operate.  Unlike most other 
+               Altus Metrum products, EasyMotor does not work with 
+               single-cell LiPo batteries.  That's because commonly
+               available inexpensive pressure sensors need 5V, which is
+               more than a single-cell LiPo provides.  Any battery that
+               provides from 6.5 to about 15 volts should work.  Good 
+               choices are the common 9V alkaline battery, or the very 
+               small and light A23 12V alkaline batteries.
+
+               Because he often mounts EasyMotor to the motor's forward 
+               bulkhead instead of to the airframe itself, Bdale often 
+               uses a length of "shooter wire" from an e-match or used 
+               motor igniter as a power switch, routing the wire out of 
+               the typical fin can vent hole and using "twist and tape" 
+               to power up the board.  Whatever works!
+
+       === Pressure Sensor
+
+               The primary motivation for designing EasyMotor was to have
+               a reliable way of recording motor chamber pressure during
+               flight.  To that end, EasyMotor supports attachment of a
+               low-cost analog pressure sensor.  The board provides 5V
+               to power the sensor, and an input for measuring and 
+               logging the output voltage from the sensor.
+
+               The kind of sensor EasyMotor is designed to work with
+               takes 5V in and has a linear analog output that ranges
+               from 0.5V at 0 to 4.5V at the maximum pressure supported
+               by the sensor.  Very inexpensive sensors that have a 
+               "1/8 NPT" threaded input, a "Buick-style" 3-pin connector,
+               and typically ship with a short cable and mating 
+               connector, are readily available on eBay and AliExpress.
+
+               To log in-flight chamber pressure, a typical approach
+               might be to drill a 1/8" sampling hole all the way 
+               through the center of the motor's forward closure, then
+               drill and tap partially through the closure with a "1/8
+               NPT" pipe tap.  Fill the touch hole with grease, screw in 
+               the pressure sensor, and attach the sensor leads to 
+               EasyMotor.