Homemade Fail safe: any help?

[rva1945]

Hi:

I just need a circuit that makes a servo travel to a preset position in case of loss of signal.

PICs are hard to find here, so I'd like to use discrete components.

I guess the circuit should detect loss of signal and trigger a relay that turns a 555 on which is configured to output a preset pulse width, or something like that.

Thanks
Robert

[Rodney]

You will probably get better help if you do two things, state your location and state what brand and type system you are using. There is quite a difference in FM, AM, PPM, PCM or 2.4GHz and in country (frequency and power allowed).

[Chippie]

You need a 555 configured to act as missing pulse detector...google will turn summat up..generally for ppm tho'

[Tomapowa]

Non-Pic-based Fail-Safe.... built many of these years ago...

http://www.laureanno.com/RC/failsafe.htm

[rva1945]

Non-Pic-based Fail-Safe.... built many of these years ago...

http://www.laureanno.com/RC/failsafe.htm


GREAT BUT, WHICH ES THE IC?

Thanks

[Dan Baldwin]

The IC is a CMOS quad 2 input nand gate; CD4011
http://www.mouser.com/Search/ProductDetail.aspx?qs=HsbVqlCqgzGaKt4meFPo1g%3d%3d

Dan

[tarmotaja]

Hi,
before you start building that Fail-Safe unit, look the Servo outputs of Receiver. If you can find Oscilloscope, that's the best. In ideal case there is no servosignal by loosing Tx signal. But sometimes will Receiver generate quite strange noise ( random pulses ) to servo outputs. Then you can't use simple solutions.

BR,
Tarmo

[pabloantoine]

There is a simple/reliable solution without any electronics involved.
I built an optical sensor working on a Futaba 6Ex /R606FS system 2.4 GHz for my blimp. The receiver has a green LED for live trans. At the loss of radio link a red LED lights up. A photocell I adapted on the case of the RX sees only the red LED when it lights up and lets current pass to a servo that pulls an arm and releases a 200 m recovery line on a spool. It works flawlessly, it uses one channel and the system is armed before starting the receiver.
It's basically just a photocell in series with the servo, waiting for the red light to come up...

[rva1945]

Nice solution. But my receiver doesn't have a led that turns off in case of loss of signal.

And 2,4 GHz systems simply don't work in submarines.

Thanks