/*
By Henderson Hood.
This code is designed to initiate communication with a DHT11 temperature 
and humidity sensor. Its main objective is to send the required start signal 
to the sensor over its 1-wire bus. After sending the start signal, the code 
configures the Raspberry Pi Pico to listen for the sensor's expected 40-bit 
data response, which includes temperature and humidity data. 
The program then enters a loop, allowing for the observation of the data 
line's activity, particularly the sensor's response, using a virtual  
logic analyzer. 
To view the 40-bit data captured here by the virtual Logic analyzer, run the program and
then exit. Save the file. Open the file in Pulseview or similar viewer to see the 
PWM based data from the DHT11. Part 2 of this Lab (LAB-DHT11-part2) will decode and 
print the temperature and humidity returned by the DHT11 on the terminal. 
*/


#include <stdio.h>
#include "pico/stdlib.h"
#include "hardware/gpio.h"

#define DHT11_PIN 5

int main() {
    stdio_init_all();
    gpio_init(DHT11_PIN);

    // Send start signal
    gpio_set_dir(DHT11_PIN, GPIO_OUT);
    sleep_ms(1);
    gpio_put(DHT11_PIN, 0);  // Pull low for at least 18ms
    sleep_ms(18);
   // Pull high for 20-40us
    gpio_set_dir(DHT11_PIN, GPIO_IN); //configure PIN as input will release the bus
    sleep_us(30); //wait for 40-bit data to be ready
    // 
  

    while (1) {
        // Keep the program running to observe the signal on an oscilloscope
        tight_loop_contents();
    }

    return 0;
}

/*
Think of this as the Pico starting a chat with the DHT11 using the 1-wire communication protocol. 
They use a single data line for this.

Here's how the code works on this 1-wire bus:
1. Initialization: The code sets up standard input/output. It also prepares the designated 
   GPIO pin (pin 5).

2. Sending the Start Signal on the 1-Wire Bus: This uses the specific behavior of 
   the 1-wire bus.
◦  Initially, the 1-wire bus is high. This is due to pull-up resistors. The DHT11 has a 
   built-in pull-up resistor.
◦  The Pico configures the GPIO pin as an output.
◦  To start, the Pico actively pulls the 1-wire bus low. It holds it low for a 
   specific time (1ms initially, then 18ms). This forces the bus from its normal high state.
◦  This prolonged low signal tells the DHT11 the host (Pico) wants to communicate.
◦  After holding it low (18ms), the code releases the 1-wire bus by setting the pin to input.
◦  Due to the DHT11's internal pull-up, the bus will return to its idle high state.
◦  A short pause (30 microseconds) allows the DHT11 to get ready to respond on 
   the high 1-wire bus.

3. Waiting and Observing the Response on the 1-Wire Bus: The code enters an infinite 
   loop to keep running. This allows you to watch the 1-wire data bus with your 
   logic analyzer. Look for the DHT11 to take control after the Pico releases it 
   (pin set to input). The DHT11 will acknowledge by pulling the 1-wire bus low briefly, 
   then high, before sending the 40-bit data.

To summarize the key points:
• Communication uses a 1-wire bus.
• The 1-wire bus is normally high due to pull-up resistors, including in the DHT11.
• The Pico starts by actively pulling the 1-wire bus low.
• After the start signal, the Pico releases the bus.
• The DHT11 then controls the 1-wire bus to send its response.

By observing the logic analyzer, you can see the pulse train (40 pulses: short pulse is '0'
long pulse is '1') on this single wire as the Pico sends the start signal and the DHT11 
tries to respond using its 1-wire protocol. Seeing the initial low pulse from the Pico, 
followed by the DHT11 pulling the line low and then high, suggests the sensor is likely working.

In part two, we will decode print this PWM encoded data into Temperature and Humidty values. 
*/