AleG recently linked to this thread (http://www.rcgroups.com/forums/showthread.php?t=973183) in response to a similar query I had, it uses Atmel chips which are different again from PICs, but seems kinda close to what you want, you can switch on or off two different devices, but by waggling the stick, not from three different stick positions.
Indeed, the code could easily be adapted to switch on the outputs when the input signal goes, for example, above 1.8ms and bellow 1.2ms.
I haven't tried it, but I suppose it could be rewritten like this:
#define F_CPU 9600000UL // 9.6MHz
#include <avr/io.h>
#include <avr/delay.h>
#include <avr/interrupt.h>
volatile unsigned int Tick; // Timer count variable
volatile unsigned char sPulse; // Incoming servo pulse measured length
volatile unsigned int sPulseIn; // Incoming servo pulse measurement
volatile unsigned char ServoCurrent; // Current position of the output servo
volatile unsigned char ServoTarget; // Target position of the output servo
unsigned char Right_1; // Stick on right position flag
unsigned char Left_1; // Stick on left position flag
unsigned int pRight; // Right sPulse threshold
unsigned int pLeft; // Left sPulse threshold
unsigned char window; // Window of opportunity to switch states
unsigned char restore_SREG; // SREG status temporary store
unsigned char ServoStep; // Step the servo in one direction
unsigned char ServoSubStep; // Controls speed of servo rotation
int main (void)
{
sei(); // Enable global interrupts
DDRB &= ~(1<<PB1); // PB1 as input
DDRB |= (1<<PB0) | (1<<PB2) | (1<<PB3) | (1<<PB4); // PB0 and PB2 as output
TCCR0A |= (1<<WGM01); // Configure timer 1 for CTC mode
TIMSK0 |= (1<<OCIE0A); // Enable CTC interrupt
OCR0A = 95; // Set CTC compare value
TCCR0B |= (1<<CS00); // No prescaler
GIMSK |= (1<<INT0); // Enable INT0 interrupt
MCUCR |= (1<<ISC00) | (1<<ISC01); // INT0 interrupt on rising edge
Tick = 0; // Initialize timer at 0
ServoCurrent = 100; // Initialize output servo at far left position
ServoTarget = 100; // Initialize output servo target at far left position
sPulse = 150; // Set initial state of pulse width
pRight = 175; // Long pulse threshold
pLeft = 125; // Short pulse threshold
window = 5; // Time window for stick motion
while(1)
{
sei(); // Enable interrupts
/*Monitor if stick is left or right*/
/*MODIFIED CODE*/
if(sPulse >= pRight) // True if stick right past threshold
{
PORTB ^= (1<<PB3); // Toggle Output A, pin 2
}
if(sPulse <= pLeft) // True if stick left past threshold
{
PORTB ^= (1<<PB4); // Toggle Output B, pin 3
}
/*MODIFIED CODE*/
}
}
ISR(TIM0_COMPA_vect) // 100KHz timer interrupt
{
restore_SREG = SREG; // Save register status
cli(); // Disable interrupts
/* Servo Out pulse generation */
if(Tick <= ServoCurrent) // While the Tick count is less than the maximum pulse length
{
PORTB |= (1<<PB0); // Keep pin 5 high
}
else
{
PORTB &= ~(1<<PB0); // Keep pin 5 low for the reminder of the servo frame
}
if(Tick >= 2000) // One servo frame (20ms) completed
{
Tick = 0; // Reset counter
}
Tick += 1; // Increment counter
sPulseIn += 1; // Increment the incoming servo pulse value
SREG = restore_SREG; // Restore status register
sei(); // Enable interrupts
}
/* Servo In pulse measurement and servo Out position setting */
ISR(INT0_vect) // Servo input interrupt
{
restore_SREG = SREG; // Save register status
cli(); // Disable interrupts
if(MCUCR & (1<<ISC00)) // If incoming servo pulse begins (rising edge)
{
sPulseIn = 0; // Start pulse count
/* Servo Out rotation speed*/
ServoSubStep += 1; // Increment servo position substep
if(ServoSubStep >= 3) // ServoSubStep >= *less faster, more slower*
{
ServoStep = 1;
ServoSubStep = 0;
}
/*Set interrupt sense to falling edge*/
MCUCR |= (1<<ISC01);
MCUCR &= ~(1<<ISC00);
}
else // If incoming servo pulse ends (falling edge)
{
if(ServoStep) // If it's time to step Servo Out in one direction
{
if(ServoCurrent < ServoTarget)
{
ServoCurrent += 1; // Step Servo Out right
}
if(ServoCurrent > ServoTarget)
{
ServoCurrent -= 1; // Step Servo Out left
}
ServoStep = 0; // Reset and wait for next servo step command
}
sPulse = sPulseIn; // Measure Servo In pulse length
/*Set interrupt sense to rising edge*/
MCUCR |= (1<<ISC00) | (1<<ISC01);
}
SREG = restore_SREG;
sei();
}
It should be tested though, since I just deleted almost all the main program routine and left some subroutines orphaned inside the interrupts.