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Add "official" support to DHT11 #1

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Add "official" support to DHT11 #1

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54cd4b6
[swift3] Update to Swift 3
viteinfinite Feb 4, 2017
bc27a49
[dht11] Support DHT11 via a configuration enum
viteinfinite Feb 4, 2017
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184 changes: 97 additions & 87 deletions dht.swift
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Original file line number Diff line number Diff line change
@@ -1,42 +1,50 @@
import Glibc
import Foundation
import SwiftyGPIO

enum DHTError: ErrorType {
case InvalidNumberOfPulses
case InvalidChecksum
enum DHTError: Error {
case invalidNumberOfPulses
case invalidChecksum
}

public class DHT {
var pin: GPIO
public enum SupportedSensor {
case dht11
case dht22
}

init(pin:GPIO) {
public class DHT {
private var pin: GPIO
private let sensor: SupportedSensor

init(pin: GPIO, for sensor: SupportedSensor) {
self.pin = pin
self.sensor = sensor
}

func setMaxPriority() {
var sched: sched_param = sched_param()
// Use FIFO scheduler with highest priority for the lowest chance of the kernel context switching.
sched.__sched_priority = sched_get_priority_max(SCHED_FIFO)
if (sched_setscheduler(0, SCHED_FIFO, &sched) != 0) {
print("ERROR")
}
// Use FIFO scheduler with highest priority for the lowest chance of the kernel context switching.
sched.__sched_priority = sched_get_priority_max(SCHED_FIFO)
if (sched_setscheduler(0, SCHED_FIFO, &sched) != 0) {
print("ERROR")
}
}

func setDefaultPriority() {
var sched: sched_param = sched_param()
// Go back to default scheduler with default 0 priority.
sched.__sched_priority = 0;
sched.__sched_priority = 0
sched_setscheduler(0, SCHED_OTHER, &sched)
}

func binaryStringForNumber(number: UInt8) -> String {
return self.binaryStringForNumber(Int(number))
func binaryString(for number: UInt8) -> String {
return binaryString(for: Int(number))
}

func binaryStringForNumber(number: Int) -> String {
let str = String(number, radix:2) //binary base
let padd = String(count: (8 - str.characters.count), repeatedValue: Character("0")) //repeat a character
return String(padd + str)
func binaryString(for number: Int) -> String {
let str = String(number, radix:2) //binary base
let padd = String(repeating: "0", count: (8 - str.characters.count)) //repeat a character
return String(padd + str)
}

func read(debug: Bool = false) throws -> (temperature: Double, humidity: Double) {
Expand All @@ -53,13 +61,13 @@ public class DHT {

// Store the count that each DHT bit pulse is low and high
// Making these arrays bigger tho cause sometimes we do catch the initial
// pulse, but sometimes usually not. yay for nonrealtime
var lowPulseTimes = [Int](count:kDHT_PULSES + 1, repeatedValue: 0)
var highPulseTimes = [Int](count:kDHT_PULSES + 1, repeatedValue: 0)

// pulse, but sometimes usually not. yay for nonrealtime
var lowPulseTimes = [Int](repeating: 0, count: kDHT_PULSES + 1)
var highPulseTimes = [Int](repeating: 0, count:kDHT_PULSES + 1)
// Set pin to output
self.pin.direction = .OUT

pin.direction = .OUT
var prevValue = 1
var lowpulse = 0
var highpulse = 0
Expand All @@ -68,7 +76,7 @@ public class DHT {
var endTime:timeval = timeval(tv_sec: 0, tv_usec: 0)

// The data sheet says the 'start signal' is having the microcontroller
// setting LOW for 1-10ms, then pull HIGH and wait for response from
// setting LOW for 1-10ms, then pull HIGH and wait for response from
// the AM2302 -- I found that if I did this, I never got good results,
// possibly because after sending LOW, I couldn't pull HIGH and
// switch to direction INPUT fast enough to start processing data?
Expand All @@ -78,104 +86,106 @@ public class DHT {
// I did find marginally better results by bumping up the priority of the thread
// but only marginally, it still fails ALOT -- A. LOT. Sampling every 5s I can
// usually get a good reading within the past 60s, many times more often than that
// but def not every time.
self.setMaxPriority()

// Set pin low
self.pin.value = 0

// but def not every time.
setMaxPriority()
// Set pin low
pin.value = 0
usleep(10000)

// see comment above
// self.pin.value = 1

// Set pin to in
self.pin.direction = .IN

pin.direction = .IN
// This is tough -- most other code I read had while loops, with
// timeouts -- i took a different approach and just spin in a for-loop
// constantly sampling the pin and comparing to the previous value.
// The end result is the same, but this way I'll never get stuck in a while-loop
// or have to mess with timeouts -- and this just makes more sense to me
gettimeofday(&startTime,nil)
gettimeofday(&startTime,nil)
for _ in 0..<5000000 {
if self.pin.value != prevValue {
gettimeofday(&endTime,nil)
let pulseTime = endTime.tv_usec - startTime.tv_usec
if pin.value != prevValue {
gettimeofday(&endTime,nil)
let pulseTime = endTime.tv_usec - startTime.tv_usec
if prevValue == 0 {
lowPulseTimes[lowpulse] = pulseTime
lowPulseTimes[lowpulse] = Int(pulseTime)
lowpulse = lowpulse + 1
} else {
highPulseTimes[highpulse] = pulseTime
highPulseTimes[highpulse] = Int(pulseTime)
highpulse = highpulse + 1
}
prevValue = self.pin.value
prevValue = pin.value
gettimeofday(&startTime,nil)
}
}

// Done with timing code, interpret the results
self.setDefaultPriority()

setDefaultPriority()
// This is a big hack -- if the timings are off, and i only get 40 pulses, I know the first one is low -- so regardless set it
// this helps us get better results -- but yeah...super hack
highPulseTimes[0] = 0


if debug {
print("LOW PULSE TIMINGS (\(lowpulse)): \(lowPulseTimes)")
print("HIGH PULSE TIMINGS (\(highpulse)): \(highPulseTimes)")
print("HIGH PULSE TIMINGS (\(highpulse)): \(highPulseTimes)")
}

guard highpulse >= 40 else { throw DHTError.InvalidNumberOfPulses }


guard highpulse >= 40 else { throw DHTError.invalidNumberOfPulses }
// Data sheet says 0bit pulses are ~28us, and 1bit pulses are ~70us
//
// this stuff with 'highSkip', are accounting for when we actually get the pulses
// during the startup signal. Usually, this is missed, but the array size and
// this offset account for that.
let highSkip = highpulse - 40
var data = [UInt8](count:5, repeatedValue: 0)
var prevIndex = 0
for i in highSkip..<(40+highSkip) {
let index = (i-highSkip) / 8
data[index] <<= 1
if prevIndex != index {
prevIndex = index
}
if highPulseTimes[i] >= 30 {
// One bit for long pulse
data[index] |= 1
}
// else zero bit for short pulse
}

// checksum is UPPER 8 BITS of the sum of the other values
let computedChecksum = (Int(data[0]) + Int(data[1]) + Int(data[2]) + Int(data[3])) & 0xFF
if debug {
print("Computed checksum: \(self.binaryStringForNumber(computedChecksum))(\(computedChecksum)) = (\(self.binaryStringForNumber(data[0]))(\(data[0])) + \(self.binaryStringForNumber(data[1]))(\(data[1])) + \(self.binaryStringForNumber(data[2]))(\(data[2])) + \(self.binaryStringForNumber(data[3]))(\(data[3]))) & 0xFF")
print(" Actual checksum: \(self.binaryStringForNumber(data[4]))(\(data[4]))")
// this offset account for that.
let highSkip = highpulse - 40
var data = [UInt8](repeating: 0, count: 5)
var prevIndex = 0
for i in highSkip..<(40+highSkip) {
let index = (i-highSkip) / 8
data[index] <<= 1
if prevIndex != index {
prevIndex = index
}
if highPulseTimes[i] >= 30 {
// One bit for long pulse
data[index] |= 1
}
// else zero bit for short pulse
}

// Verify checksum of received data
if (data[4] == UInt8(computedChecksum)) {
// DHT11
// humidity = Double(data[0])
// temperature = Double(data[2])

// only doing DHT22 for now
humidity = ((Double(data[0]) * 256.0) + Double(data[1])) / 10.0
temperature = ((Double(data[2] & 0x7F) * 256.0) + Double(data[3])) / 10.0
if ((data[2] & 0x80) != 0) {
temperature = temperature * -1.0
}
temperature = (temperature * 1.8) + 32
} else {
throw DHTError.InvalidChecksum
}

// checksum is UPPER 8 BITS of the sum of the other values
let computedChecksum = (Int(data[0]) + Int(data[1]) + Int(data[2]) + Int(data[3])) & 0xFF
if debug {
print("Computed checksum: \(binaryString(for: computedChecksum))(\(computedChecksum)) = (\(binaryString(for: data[0]))(\(data[0])) + \(binaryString(for: data[1]))(\(data[1])) + \(binaryString(for: data[2]))(\(data[2])) + \(binaryString(for: data[3]))(\(data[3]))) & 0xFF")
print(" Actual checksum: \(binaryString(for: data[4]))(\(data[4]))")
}

// Verify checksum of received data
if data[4] == UInt8(computedChecksum) {
switch sensor {
case .dht11:
humidity = Double(data[0])
temperature = Double(data[2])
default:
humidity = ((Double(data[0]) * 256.0) + Double(data[1])) / 10.0
temperature = ((Double(data[2] & 0x7F) * 256.0) + Double(data[3])) / 10.0
}

if ((data[2] & 0x80) != 0) {
temperature = temperature * -1.0
}
temperature = (temperature * 1.8) + 32
} else {
throw DHTError.invalidChecksum
}

if debug { print("----------------------------------")}

return (temperature,humidity)
}
}
}
73 changes: 36 additions & 37 deletions main.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -2,46 +2,45 @@ import Glibc
import Foundation

func initLCD() -> HD44780LCD {
let gpios = SwiftyGPIO.getGPIOsForBoard(.RaspberryPiRev2)
let gpios = SwiftyGPIO.GPIOs(for: .RaspberryPi2)
let lcd = HD44780LCD(rs:gpios[.P25]!,e:gpios[.P24]!,d7:gpios[.P22]!,d6:gpios[.P27]!,d5:gpios[.P17]!,d4:gpios[.P23]!,width:20,height:4)
return lcd
return lcd
}

let gpios = SwiftyGPIO.getGPIOsForBoard(.RaspberryPiRev2)
let lcd = initLCD()
let gpios = SwiftyGPIO.GPIOs(for: .RaspberryPi2)
let lcd = initLCD()
lcd.clearScreen()
lcd.cursorHome()

let dht = DHT(pin: gpios[.P4]!, for: .dht22)

var temperature = 0.0
var humidity = 0.0

// samples every 5s, outputs last good temp/humidty & the # of seconds since last good reading
var startTime:timeval = timeval(tv_sec: 0, tv_usec: 0)
var endTime:timeval = timeval(tv_sec: 0, tv_usec: 0)

gettimeofday(&startTime,nil)
while (true) {
do {
(temperature,humidity) = try dht.read(true)
gettimeofday(&startTime,nil)
print("temp: \(temperature) hum: \(humidity)")
} catch (DHTError.invalidNumberOfPulses) {
let errorMessage = "INVALID PULSES"
print(errorMessage)
} catch (DHTError.invalidChecksum) {
let errorMessage = "INVALID CHECKSUM"
print(errorMessage)
}

gettimeofday(&endTime,nil)

lcd.clearScreen()
lcd.cursorHome()

let dht = DHT(pin: gpios[.P4]!)

var temperature = 0.0
var humidity = 0.0

// samples every 5s, outputs last good temp/humidty & the # of seconds since last good reading
var startTime:timeval = timeval(tv_sec: 0, tv_usec: 0)
var endTime:timeval = timeval(tv_sec: 0, tv_usec: 0)

gettimeofday(&startTime,nil)
while (true) {
do {
(temperature,humidity) = try dht.read(true)
gettimeofday(&startTime,nil)
print("temp: \(temperature) hum: \(humidity)")
} catch (DHTError.InvalidNumberOfPulses) {
let errorMessage = "INVALID PULSES"
print(errorMessage)
} catch (DHTError.InvalidChecksum) {
let errorMessage = "INVALID CHECKSUM"
print(errorMessage)
}

gettimeofday(&endTime,nil)

lcd.clearScreen()
lcd.cursorHome()
lcd.printString(0,y:0,what:"Temp: \(temperature) \(endTime.tv_sec - startTime.tv_sec)s",usCharSet:true)
lcd.printString(0,y:1,what:"Humidity: \(humidity)",usCharSet:true)
lcd.printString(0,y:0,what:"Temp: \(temperature) \(endTime.tv_sec - startTime.tv_sec)s",usCharSet:true)
lcd.printString(0,y:1,what:"Humidity: \(humidity)",usCharSet:true)

sleep(5)
}

sleep(5)
}