This an Open-Source multiplexor that will allow you switch between manual or auto mode using only one channel of your remote control, also include a "build-in" picoswitch
with three states (down, middle and up) + reset mode, and all through one channel.
This MUX is intended to be use in low power and simple autopilot systems. In case your uController do not have enough timers to control servos, you should try the pololu servo controller
and interface it with the DIY MUX.
The attiny firmware is also Open-Source and you can modify it as you wish, you will need winavr+avrstudio4 and of course an ISCP programmer, like this one
To buy a PCB click here
Part list from DigiKey:
3 x 1k SMD(0805) resistor P1.00KCCT-ND
1 x 10k SMD resistor P10.0KCCT-ND
1 x .1uf capacitor PCC1828CT-ND
2 x LEDs SMD(0603), the color is optional:
1 x Attiny 85, ATTINY85V-10SU-ND
1 x Mux 74LS157 296-14884-1-ND
There is also an optional component (D1), (in the top of PSEL label on the schematics), this is just a protection diode, if you are not planning to use it you should make a solder bridge between the pads..
Just to remember, when i used to have no idea of basic PCB design rules:
Now i try to fallow some rules, for example NEVER use the autorouter. 100% by hand..