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RCremote (Can also be used to control 8(+?) servos)

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First post! Hello, I'm currently making a RC remote for my quadcopter which I am in the process of building. The idea is to output a ppm frame which then goes into a FrSky module which beams it to a receiver on my quadcopter. I currently have the code for ppm generation done. I am reading up on i2c with the UCSI module in the msp430g2553 right now and will hook it up to a wii nunchuk for testing. The end product will have recycled gymbals from an esky transmitter remote hooked up to it's own microcontroller acting as an i2c slave to the ppm generation microcontroller.



int Pnum = 1; //Stores the number of pulses triggered so far in current ppm frame
int servo[8] = {1000,1150,1300,1450,1500,1750,1900,2000}; // Servo pulse values

void main(void)
WDTCTL = WDTPW|WDTHOLD; //stop watchdog timer


P1OUT = BIT6|BIT0; //Preload P1.2 on 
P1DIR = BIT6|BIT0; //Set P1.2 to output

TA0CCR0 = 100;	 //Timerinitiallycountsuptothisvalue.Mustbelongenoughforeverythingtosetup
TA0CCTL0 = CCIE; //Enable interrupts on CCR0

TA1CCR0 = 20000; //Length of PPM frame minus one

TA0CTL = MC_1|ID_0|TASSEL_2|TACLR; //Setup TimerA0 (up mode|clock divide by 1|SMCLK|Clear timer)
TA1CTL = MC_1|ID_0|TASSEL_2|TACLR; //Setup TimerA1 (up mode|clock divide by 1|SMCLK|Clear timer)

__enable_interrupt();	 //enable interrupts

for(; //infinite loop

#pragma vector = TIMER0_A0_VECTOR //T0A0_ISR
__interrupt void T0A0_ISR (void)
P1OUT &= ~BIT6;
P1OUT |= BIT6;
if(Pnum != 9)
	TA0CCR0 = servo[(Pnum-1)]; //Servo pulse
	Pnum++; //increment Pnum

	TA0CCR0 = (20000-(TA1R)); //Sync pulse
	Pnum = 1;	 //Reset Pnum

This is the code I have right now. The way it works is Timer0 is set to count up to the value in TA0CCR0 (the length of the servo pulse). When TA0CCR0 overflows an interuppt is requested and the interrupt service routine T0A0_ISR runs. T0A0_ISR changes the value of TA0CCR0 to the next value in the array servo. After 8 pulses TA0CCR0 is set to fill in the time remaining until 20ms has passed since the start of the ppm frame. This is done by setting Timer1 to count up to 20 000 (TA1CCR0), after the 8th pulse TA0CCR0 is set to 20 000 minus the amount that Timer1 has currently counted up to, thus giving the time remaing until the end of the 20 ms.


The positions of the servos are stored in the array servo as the length of each servo pulse. This array can be modified in the main loop.


This code can also be used to control 8 or more(i think, depends how many pulses you can fit in a 20ms period) servos through 1 pin (selectable). All that is required is a 4017 decade counter to demultiplex the ppm signal into standard servo pwm.


But there's a catch. I actually haven't tested any of this code in real life. (I accidentally killed 3 servos somehow before making this) My pickit2 logic analyzer shows me that everything is working fine though.


Thanks for reading.


edit: fixed array values, should range from 1000 - 2000 not 500 - 1500

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Such perfect timing!

This is exactly what I need for the halloween decoration i'm making.

I'll use this to control the mouths of 8 small jack-o-lanterns (see evil mad scientist labs' "snap-o-lantern) and make them "sing" a different note each, to play "tubular bells" (the theme to "The Exorcist")

I'll ptobably make each pumpkin lit up with a different coloref LED also, to emphasize that each is a different note.



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  • 8 years later...

i have build a homemade ppm decoder with CD4017 ic together with 27mhz fm transmitter and receiver. The 27mhz transmitter/receiver work correctly because i can hear the tune when connected to a small speaker, but the problem here is: despite that the encoder and the decoder working correctly when connected via negative and signal terminal directly to the decoder, it refuses to work with the remote module that i made and i dont know why is happening so. is there anyone who can tell me the problem?

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