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Multi-channel Failsafe for Radio Controlled Models

Happy landings!

If you do not want your expensive R/C model to crash or disappear forever when the radio link fails or is subject to heavy interference, you need to preload your model with servo settings that ‘take over’ under adverse radio or battery conditions ensuring a landing that’s as gentle and safe as possible. This circuit does it all, and more!The Multi-Channel Failsafe was developed to prevent damage to radio controlled models when the on-board radio control receiver starts to receive erratic control information, or when the craft supply voltage drops below a predefined ‘safe’ level. Detection of corrupt frames in the received signal is handled by a microcontroller. At a certain level of insecurity, the micro loads a number of servo settings from an EEPROM that (hopefully) result in a safe landing, or at least, minimum damage to the model. The most important setting in these cases is, without doubt: cut off the engine (i.e., get it to idle)!
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Component list
R1 = 470Ohm
R2-R9 = 1kOhm
R10 = 8-way 2kOhm 2 SIL array
R11,R12 = 4kOhm 7
R13 = 15kOhm
R14 = 2kOhm 2
R15 = 56kOhm
R16 = 6kOhm 8
P1 = 5kOhm preset H
C1,C7,C8,C9 = 100nF
C2 = 1µF 16V radial
C3 = 10nF
C4 = 100µF 16V radial
C5,C6 = 22pF
D1 = BAT85
D2,D3 = 1N4148
IC1 = AT89C52-24JI, programmed, order code 020382-41
IC2 = 24LC01 (2V7)
IC3 = LM393
IC4 = LM2931AZ5 (Farnell # 412480)
BZ1 = active (DC) buzzer, 5V
K1-K8 = 3-way servo plug
K9-K16 = 3-way SIL pinheader
S1 = 2-way DIP-switch (3-way optional, one contact not used)
S2 = pushbutton, 1 make contact
X1 = 11.0592MHz quartz crystal
PCB, order code 020382-1
Disk, microcontroller source code, order code 020382-11 or Free Download
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