Free Flight Model Aircraft Dethermalizing Timer

INTRODUCTION
This application is for a Free Flight Dethermalizing
Timer for Model Aircraft. This is usually a mechanical or
fuse timer which spoils the lift of a model aircraft after 5
minutes. This is to prevent losing the aircraft in a strong
atmospheric thermal.
Using a bicolor LED and pushbuttons, a delay time of
between two and seven minutes in 10 second increments
is indicated B1 places the device in program mode and the LED
shows green. B2 then enters the number of 10 second
intervals with the LED flashing red for each interval in
groups of 5 for ease of reading. After the interval is
loaded, the timer is armed by pressing B2 again. When
armed the LED goes red. To start the timer, B2 is
pressed and held. The timer starts on release of B2.
When the unit times out, the 2N2222 is turned on, the
wire heats and contacts, and the control surface is
actuated and the 2N2222 is deactivated.
Nictol wire is a shape memory nickel titanium alloy
which contracts 3.5% of its length when heated. Nictol
wire also has a high resistance similar to nichrome
wire. Using 6-10 mil wire, 200 mA will heat the wire to
its activation temperature.