Microchip PIC10F202 RC滑翔机开关Timer0计数LED控制故障求助

Hey there, let’s troubleshoot that stubborn LED issue with your PIC10F202 RC switch. I’ve tinkered with plenty of microcontroller-based RC projects, so let’s break down what might be going wrong and how to fix it.

Before diving into code, let’s eliminate simple hardware issues that often cause this kind of problem:

• GP2 Input Wiring: Double-check your PPM signal connection to GP2. Does the signal have proper 3.3V/5V levels matching the PIC’s IO specs? Add a 10kΩ pull-down resistor to GP2 if you haven’t already—floating inputs can cause false triggers or stuck states.
• LED Configuration: Which IO pin is your LED connected to? Make sure it’s configured as an output (TRIS bit set to 0) and that you’ve added a 220-330Ω current-limiting resistor. If you’re driving the LED directly from the IO, confirm you’re using the correct current direction (PICs sink current better than source, so tying the LED to VCC and the IO pin to ground often works more reliably).
• Power & Ground: Ensure your PIC and RC receiver share a common ground. PPM signals rely on a reference ground to be detected correctly—no ground connection means the PIC can’t interpret the signal at all.

Your configuration bits and setup code are critical here. Let’s verify key settings:

• Timer0 for T0CKI: Make sure you’ve set OPTION_REG correctly for rising-edge detection:
  • T0CS = 1: Selects external T0CKI pin as Timer0 clock source
  • T0SE = 0: Triggers on rising edges (what you specified)
  • PSA = 0: Assigns the prescaler to Timer0 (adjust the prescaler value based on your clock speed to avoid overflowing too quickly)
• IO Direction: Confirm TRISIO2 is set to 1 (GP2 as input) and your LED’s TRIS bit is set to 0 (output).
• Oscillator & Watchdog: Ensure your configuration bits enable the internal oscillator (e.g., IOSCFS_4MHZ) and disable the watchdog timer (WDTE_OFF) unless you’re explicitly feeding it in code. A stuck watchdog can cause unexpected resets or frozen behavior.

PPM signals work by using pulse position to encode channel data (a 20ms frame with 1-2ms pulses per channel). If your LED is always on, your logic might be misinterpreting the signal or defaulting to the "on" state. Here’s a simplified, corrected approach for your C code:

#include <pic10f202.h>

// Configuration bits (adjust based on your hardware)
__CONFIG(FOSC_INTRC & WDTE_OFF & PWRTE_ON & MCLRE_OFF & CP_OFF & IOSCFS_4MHZ);

#define LED_PIN GP0
#define PPM_PIN GP2

void init(void) {
    // Set IO directions: GP2 = input, GP0 = output
    TRISIO = 0b00000100;
    // Configure Timer0 for T0CKI rising-edge counting
    OPTION_REG = 0b00000000; // T0CS=1, T0SE=0, PSA=0, PS=000 (1:1 prescaler)
    // Initialize LED to OFF
    LED_PIN = 0;
    // Reset Timer0 and overflow flag
    TMR0 = 0;
    INTCONbits.T0IF = 0;
}

void main(void) {
    init();
    unsigned char last_tmr0 = 0;
    unsigned char overflow_count = 0;
    unsigned char channel_counter = 0;

    while(1) {
        // Handle Timer0 overflow
        if(INTCONbits.T0IF) {
            overflow_count++;
            INTCONbits.T0IF = 0;
        }

        // Detect rising edge (TMR0 increments)
        if(TMR0 != last_tmr0) {
            // Calculate time between rising edges
            unsigned char diff = TMR0 - last_tmr0;
            unsigned int total_cycles = (overflow_count * 256) + diff;
            // Convert cycles to ms (4MHz clock = 0.25us per cycle)
            float pulse_interval_ms = (total_cycles * 0.25) / 1000;

            // Reset for new frame (sync pulse is ~4ms for most PPM signals)
            if(pulse_interval_ms > 3.5) {
                channel_counter = 0;
                overflow_count = 0;
            } else {
                channel_counter++;
                // Trigger LED on channel 3 (adjust to your desired channel)
                if(channel_counter == 3) {
                    // Turn LED ON if pulse is >1.5ms (RC "high" position), OFF otherwise
                    LED_PIN = (pulse_interval_ms > 1.5) ? 1 : 0;
                }
            }

            last_tmr0 = TMR0;
        }
    }
}

Key fixes in this code:

• Tracks Timer0 overflows to handle the full 20ms PPM frame (8-bit Timer0 alone can’t count that long)
• Detects the PPM sync pulse to reset channel counting
• Explicitly sets the LED to OFF on startup, then toggles based on your desired channel’s pulse width

• Use an oscilloscope to verify the PPM signal on GP2—make sure you’re getting valid pulses (1-2ms per channel, 20ms frame).
• Add a second debug LED (e.g., on GP1) that blinks every time a rising edge is detected. This will confirm if your PIC is actually seeing the PPM signal.
• Check the LED pin’s voltage with a multimeter—if it’s stuck at VCC or ground, your IO configuration is likely wrong.

内容的提问来源于stack exchange，提问作者Teodor Teodorovicz