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Build an RC Plane Finder
The lost plane finder introduced here is
a little on board beacon, also known as lost model alarm/crashed
aircraft beacon, which helps you find a crashed or downed
radio-controlled plane. The concept is to get an alert from a piezo
sounder if there are no signals from the associated radio-controlled
transmitter.
Usually, the radio transmitter provides a
set of pulses every 20 milliseconds, which, in turn, sends the radio
receiver a separate pulse to each of the servos at the same interval. In
this circuit, an alarm will sound when the radio receiver no longer
receives the set of pulses from the radio transmitter.
Fig. 1: A typical lost plane finder
To locate the aircraft, all you have to
do is switch your transmitter off and the system will start to beep. The
circuit is very easy to build and does not require any special parts
like costly microcontrollers. A typical lost plane finder is shown in
Fig. 1.
Circuit and working
Circuit diagram of the lost plane finder
is shown in Fig. 2. It is built around timer NE555 (IC1), one
transistor BC547 (T1) and a few other components. The design is centred
around timer chip NE555 (IC1), configured here as a missing-pulse
sensor. The whole circuit can be powered with power supplies ranging
from 4V up to 9V, so you can use any power source that your radio
receiver/servo setup can handle.
Fig. 2: Circuit diagram of the lost plane finder
The 4-pin connector (CON2) is the input
connector for the lost plane finder system, while the 2-pin connector
(CON3) is an optional output connector. In the circuit, when the pulse
input is available at input pin 4 of CON2, BC547 transistor (T1) is
turned on and a high-level (H) voltage (near 2.6V when Vcc=4V) is
available through output pin 3 of NE555 (IC1). When the pulse input is
absent (transmitter is off), T1 switches off and IC1 gives a low-level
(L) output through its output pin 3.
As a result, the piezo buzzer (PZ1) and
the indicator (LED1) wake up to raise a noticeable alert. Presence of
the optional output connector (CON3) enables driving of external
low-voltage blinker/beeper loads, in case of an extreme demand for such
enhancements.
Construction and testing
An actual-size, single-side PCB for the
lost plane finder circuit is shown in Fig. 3 and its component layout in
Fig.4. After assembling the circuit on a PCB, enclose it in a plastic
case. A tiny perfboard is enough for the construction of the lost plane
finder system. After construction, it is better to make the system
vibration proof with the help of a heat-shrink tube, preferably a
transparent type with appropriate diameter. Connect the finished system
to any unused channel of your radio receiver through the input connector
(CON2) as shown in the wiring diagram in Fig. 5.
Fig. 3: Actual-size PCB pattern of the lost plane finderFig. 4: Component layout of the PCBFig. 5: Wiring diagram
If a free radio receiver channel is not
available, the system can still be utilised by sharing an occupied
channel with some other intermittently-used control like landing gear,
flaps or airbrakes, with the help of a Y- Splitter servo cable attached
to such a channel.
Fig. 6: Author’s prototype
The preferred setup in the model
aircraft suggests drilling a small hole in the model wall and attaching
the system so that its sounder window is aligned with the hole.
Depending on your aircraft model’s structure, the whole system can be
completely exposed outside of the model, too. Author’s prototype is
shown in Fig. 6.
Additional notes
1. Prototype was tested with R/C lithiun-polymer 2S battery (7.4V).
2. Offline test is possible by feeding servo pulses to J1 from a standard servo tester.
3. An intermittent-tone piezo buzzer (sound level 85dB to 92dB) is better than a continuous-tone type.
4. In case of an alarm malfunction,
change the value of RC components (R2-C2) so that effective delay is
about 30 per cent to 40 per cent bigger than the period of inputted
servo pulses.
5. For a micro-size version, try to use SMD components on a stamp-size PCB.
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