hx711.py 12 KB
Newer Older
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426
#

import RPi.GPIO as GPIO
import time
import threading



class HX711:

    def __init__(self, dout, pd_sck, gain=128):
        self.PD_SCK = pd_sck

        self.DOUT = dout

        # Mutex for reading from the HX711, in case multiple threads in client
        # software try to access get values from the class at the same time.
        self.readLock = threading.Lock()
        
        GPIO.setmode(GPIO.BCM)
        GPIO.setup(self.PD_SCK, GPIO.OUT)
        GPIO.setup(self.DOUT, GPIO.IN)

        self.GAIN = 0

        # The value returned by the hx711 that corresponds to your reference
        # unit AFTER dividing by the SCALE.
        self.REFERENCE_UNIT = 1
        self.REFERENCE_UNIT_B = 1

        self.OFFSET = 1
        self.OFFSET_B = 1
        self.lastVal = int(0)

        self.DEBUG_PRINTING = False

        self.byte_format = 'MSB'
        self.bit_format = 'MSB'

        self.set_gain(gain)

        # Think about whether this is necessary.
        time.sleep(1)

        
    def convertFromTwosComplement24bit(self, inputValue):
        return -(inputValue & 0x800000) + (inputValue & 0x7fffff)

    
    def is_ready(self):
        return GPIO.input(self.DOUT) == 0

    
    def set_gain(self, gain):
        if gain is 128:
            self.GAIN = 1
        elif gain is 64:
            self.GAIN = 3
        elif gain is 32:
            self.GAIN = 2

        GPIO.output(self.PD_SCK, False)

        # Read out a set of raw bytes and throw it away.
        self.readRawBytes()

        
    def get_gain(self):
        if self.GAIN == 1:
            return 128
        if self.GAIN == 3:
            return 64
        if self.GAIN == 2:
            return 32

        # Shouldn't get here.
        return 0
        

    def readNextBit(self):
       # Clock HX711 Digital Serial Clock (PD_SCK).  DOUT will be
       # ready 1us after PD_SCK rising edge, so we sample after
       # lowering PD_SCL, when we know DOUT will be stable.
       GPIO.output(self.PD_SCK, True)
       GPIO.output(self.PD_SCK, False)
       value = GPIO.input(self.DOUT)

       # Convert Boolean to int and return it.
       return int(value)


    def readNextByte(self):
       byteValue = 0

       # Read bits and build the byte from top, or bottom, depending
       # on whether we are in MSB or LSB bit mode.
       for x in range(8):
          if self.bit_format == 'MSB':
             byteValue <<= 1
             byteValue |= self.readNextBit()
          else:
             byteValue >>= 1              
             byteValue |= self.readNextBit() * 0x80

       # Return the packed byte.
       return byteValue 
        

    def readRawBytes(self):
        # Wait for and get the Read Lock, incase another thread is already
        # driving the HX711 serial interface.
        self.readLock.acquire()

        # Wait until HX711 is ready for us to read a sample.
        while not self.is_ready():
           pass

        # Read three bytes of data from the HX711.
        firstByte  = self.readNextByte()
        secondByte = self.readNextByte()
        thirdByte  = self.readNextByte()

        # HX711 Channel and gain factor are set by number of bits read
        # after 24 data bits.
        for i in range(self.GAIN):
           # Clock a bit out of the HX711 and throw it away.
           self.readNextBit()

        # Release the Read Lock, now that we've finished driving the HX711
        # serial interface.
        self.readLock.release()           

        # Depending on how we're configured, return an orderd list of raw byte
        # values.
        if self.byte_format == 'LSB':
           return [thirdByte, secondByte, firstByte]
        else:
           return [firstByte, secondByte, thirdByte]


    def read_long(self):
        # Get a sample from the HX711 in the form of raw bytes.
        dataBytes = self.readRawBytes()


        if self.DEBUG_PRINTING:
            print(dataBytes,)
        
        # Join the raw bytes into a single 24bit 2s complement value.
        twosComplementValue = ((dataBytes[0] << 16) |
                               (dataBytes[1] << 8)  |
                               dataBytes[2])

        if self.DEBUG_PRINTING:
            print("Twos: 0x%06x" % twosComplementValue)
        
        # Convert from 24bit twos-complement to a signed value.
        signedIntValue = self.convertFromTwosComplement24bit(twosComplementValue)

        # Record the latest sample value we've read.
        self.lastVal = signedIntValue

        # Return the sample value we've read from the HX711.
        return int(signedIntValue)

    
    def read_average(self, times=3):
        # Make sure we've been asked to take a rational amount of samples.
        if times <= 0:
            raise ValueError("HX711()::read_average(): times must >= 1!!")

        # If we're only average across one value, just read it and return it.
        if times == 1:
            return self.read_long()

        # If we're averaging across a low amount of values, just take the
        # median.
        if times < 5:
            return self.read_median(times)

        # If we're taking a lot of samples, we'll collect them in a list, remove
        # the outliers, then take the mean of the remaining set.
        valueList = []

        for x in range(times):
            valueList += [self.read_long()]

        valueList.sort()

        # We'll be trimming 20% of outlier samples from top and bottom of collected set.
        trimAmount = int(len(valueList) * 0.2)

        # Trim the edge case values.
        valueList = valueList[trimAmount:-trimAmount]

        # Return the mean of remaining samples.
        return sum(valueList) / len(valueList)


    # A median-based read method, might help when getting random value spikes
    # for unknown or CPU-related reasons
    def read_median(self, times=3):
       if times <= 0:
          raise ValueError("HX711::read_median(): times must be greater than zero!")
      
       # If times == 1, just return a single reading.
       if times == 1:
          return self.read_long()

       valueList = []

       for x in range(times):
          valueList += [self.read_long()]

       valueList.sort()

       # If times is odd we can just take the centre value.
       if (times & 0x1) == 0x1:
          return valueList[len(valueList) // 2]
       else:
          # If times is even we have to take the arithmetic mean of
          # the two middle values.
          midpoint = len(valueList) / 2
          return sum(valueList[midpoint:midpoint+2]) / 2.0


    # Compatibility function, uses channel A version
    def get_value(self, times=3):
        return self.get_value_A(times)


    def get_value_A(self, times=3):
        return self.read_median(times) - self.get_offset_A()


    def get_value_B(self, times=3):
        # for channel B, we need to set_gain(32)
        g = self.get_gain()
        self.set_gain(32)
        value = self.read_median(times) - self.get_offset_B()
        self.set_gain(g)
        return value

    # Compatibility function, uses channel A version
    def get_weight(self, times=3):
        return self.get_weight_A(times)


    def get_weight_A(self, times=3):
        value = self.get_value_A(times)
        value = value / self.REFERENCE_UNIT
        return value

    def get_weight_B(self, times=3):
        value = self.get_value_B(times)
        value = value / self.REFERENCE_UNIT_B
        return value

    
    # Sets tare for channel A for compatibility purposes
    def tare(self, times=15):
        self.tare_A(times)
    
    
    def tare_A(self, times=15):
        # Backup REFERENCE_UNIT value
        backupReferenceUnit = self.get_reference_unit_A()
        self.set_reference_unit_A(1)
        
        value = self.read_average(times)

        if self.DEBUG_PRINTING:
            print("Tare A value:", value)
        
        self.set_offset_A(value)

        # Restore the reference unit, now that we've got our offset.
        self.set_reference_unit_A(backupReferenceUnit)

        return value


    def tare_B(self, times=15):
        # Backup REFERENCE_UNIT value
        backupReferenceUnit = self.get_reference_unit_B()
        self.set_reference_unit_B(1)

        # for channel B, we need to set_gain(32)
        backupGain = self.get_gain()
        self.set_gain(32)

        value = self.read_average(times)

        if self.DEBUG_PRINTING:
            print("Tare B value:", value)
        
        self.set_offset_B(value)

        # Restore gain/channel/reference unit settings.
        self.set_gain(backupGain)
        self.set_reference_unit_B(backupReferenceUnit)
       
        return value


    
    def set_reading_format(self, byte_format="LSB", bit_format="MSB"):
        if byte_format == "LSB":
            self.byte_format = byte_format
        elif byte_format == "MSB":
            self.byte_format = byte_format
        else:
            raise ValueError("Unrecognised byte_format: \"%s\"" % byte_format)

        if bit_format == "LSB":
            self.bit_format = bit_format
        elif bit_format == "MSB":
            self.bit_format = bit_format
        else:
            raise ValueError("Unrecognised bitformat: \"%s\"" % bit_format)

            


    # sets offset for channel A for compatibility reasons
    def set_offset(self, offset):
        self.set_offset_A(offset)

    def set_offset_A(self, offset):
        self.OFFSET = offset

    def set_offset_B(self, offset):
        self.OFFSET_B = offset

    def get_offset(self):
        return self.get_offset_A()

    def get_offset_A(self):
        return self.OFFSET

    def get_offset_B(self):
        return self.OFFSET_B


    
    def set_reference_unit(self, reference_unit):
        self.set_reference_unit_A(reference_unit)

        
    def set_reference_unit_A(self, reference_unit):
        # Make sure we aren't asked to use an invalid reference unit.
        if reference_unit == 0:
            raise ValueError("HX711::set_reference_unit_A() can't accept 0 as a reference unit!")
            return

        self.REFERENCE_UNIT = reference_unit

        
    def set_reference_unit_B(self, reference_unit):
        # Make sure we aren't asked to use an invalid reference unit.
        if reference_unit == 0:
            raise ValueError("HX711::set_reference_unit_A() can't accept 0 as a reference unit!")
            return

        self.REFERENCE_UNIT_B = reference_unit


    def get_reference_unit(self):
        return get_reference_unit_A()

        
    def get_reference_unit_A(self):
        return self.REFERENCE_UNIT

        
    def get_reference_unit_B(self):
        return self.REFERENCE_UNIT_B
        
        
    def power_down(self):
        # Wait for and get the Read Lock, incase another thread is already
        # driving the HX711 serial interface.
        self.readLock.acquire()

        # Cause a rising edge on HX711 Digital Serial Clock (PD_SCK).  We then
        # leave it held up and wait 100 us.  After 60us the HX711 should be
        # powered down.
        GPIO.output(self.PD_SCK, False)
        GPIO.output(self.PD_SCK, True)

        time.sleep(0.0001)

        # Release the Read Lock, now that we've finished driving the HX711
        # serial interface.
        self.readLock.release()           


    def power_up(self):
        # Wait for and get the Read Lock, incase another thread is already
        # driving the HX711 serial interface.
        self.readLock.acquire()

        # Lower the HX711 Digital Serial Clock (PD_SCK) line.
        GPIO.output(self.PD_SCK, False)

        # Wait 100 us for the HX711 to power back up.
        time.sleep(0.0001)

        # Release the Read Lock, now that we've finished driving the HX711
        # serial interface.
        self.readLock.release()

        # HX711 will now be defaulted to Channel A with gain of 128.  If this
        # isn't what client software has requested from us, take a sample and
        # throw it away, so that next sample from the HX711 will be from the
        # correct channel/gain.
        if self.get_gain() != 128:
            self.readRawBytes()


    def reset(self):
        self.power_down()
        self.power_up()


# EOF - hx711.py