From d5e9eb31cd0bbdfbc2736fc56a395885bc726ff3 Mon Sep 17 00:00:00 2001
From: Daniel Ledda <ledda@cip.ifi.lmu.de>
Date: Sat, 31 Oct 2020 15:08:45 +0100
Subject: [PATCH] First try!

---
 main.go | 103 ++++++++++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 85 insertions(+), 18 deletions(-)

diff --git a/main.go b/main.go
index d7ef77d..c6d3e1c 100644
--- a/main.go
+++ b/main.go
@@ -2,44 +2,111 @@ package main
 
 import (
 	"fmt"
+	"github.com/pkg/errors"
+	"github.com/warthog618/gpio"
+	"math"
 	"os"
 	"os/signal"
 	"syscall"
 	"time"
-
-	"github.com/warthog618/gpio"
 )
 
-// Watches GPIO 4 (J8 7) and reports when it changes state.
+const Timeout = math.MaxInt32
+const TimeoutErrInitial string = "Timed out waiting for sensor's initial %s reading!"
+
+var oneSecondInCycles = (func() int {
+	count := 0
+	start := time.Now().Nanosecond()
+	for {
+		count++
+		if time.Now().Nanosecond() - start >= 1000000 {
+			break
+		}
+	}
+	return count
+})()
+
 func main() {
 	err := gpio.Open()
 	if err != nil {
 		panic(err)
 	}
 	defer gpio.Close()
+
 	pinNumber := gpio.GPIO7
 	pin := gpio.NewPin(pinNumber)
-	pin.Input()
-	pin.PullUp()
+	result, err := readDataFromDHT(pin)
+	if err != nil {
+		fmt.Printf("Bad read! Reason: %s", err.Error())
+	} else {
+		fmt.Println(result)
+	}
 
 	// capture exit signals to ensure resources are released on exit.
 	quit := make(chan os.Signal, 1)
 	signal.Notify(quit, syscall.SIGINT, syscall.SIGTERM)
 	defer signal.Stop(quit)
 
-	err = pin.Watch(gpio.EdgeBoth, func(pin *gpio.Pin) {
-		fmt.Printf("Pin %v is %v", pinNumber, pin.Read())
-	})
-	if err != nil {
-		panic(err)
-	}
-	defer pin.Unwatch()
+	<-quit
+}
 
-	// In a real application the main thread would do something useful here.
-	// But we'll just run for a minute then exit.
-	fmt.Printf("Watching Pin %v...", pinNumber)
-	select {
-	case <-time.After(time.Minute):
-	case <-quit:
+func readDataFromDHT(pin *gpio.Pin) ([4]byte, error) {
+	receivedInput := [4]byte{0, 0, 0, 0}
+	// Setup
+	pin.PullUp()
+
+	// Send start signal
+	pin.Low()
+	pin.Output()
+	time.Sleep(1100 * time.Microsecond)
+	pin.Input()
+	pin.PullUp()
+	time.Sleep(40 * time.Microsecond)
+
+	// Get Data
+	if cyclesForReading(pin, gpio.Low) == Timeout {
+		return receivedInput, errors.New(fmt.Sprintf(TimeoutErrInitial, "low"))
 	}
+	if cyclesForReading(pin, gpio.High) == Timeout {
+		return receivedInput, errors.New(fmt.Sprintf(TimeoutErrInitial, "high"))
+	}
+
+	// Store cycle number for each low and high pulse
+	cycles := [80]int{}
+	for i := 0; i < 80; i += 2 {
+		cycles[i] = cyclesForReading(pin, gpio.Low)
+		cycles[i + 1] = cyclesForReading(pin, gpio.High)
+	}
+
+	err := storeCycleCountsAsBinarySequence(&receivedInput, &cycles)
+	if err != nil {
+		return receivedInput, err
+	}
+
+	return receivedInput, nil
+}
+
+func storeCycleCountsAsBinarySequence(store *[4]byte, cycles *[80]int) error {
+	for i := 0; i < 40; i++ {
+		lowCycles := cycles[2 * i]
+		highCycles := cycles[2 * i + 1]
+		if (lowCycles == Timeout) || (highCycles == Timeout) {
+			return errors.New("Timed out waiting for sensor pulse!")
+		}
+		store[i / 8] <<= 1
+		if highCycles > lowCycles {
+			store[i / 8] |= 1
+		}
+	}
+}
+
+func cyclesForReading(pin *gpio.Pin, level gpio.Level) int {
+	count := 0
+	for pin.Read() == level {
+		count++
+		if count >= oneSecondInCycles {
+			return Timeout
+		}
+	}
+	return count
 }
\ No newline at end of file