wensn.py

import usb.core

# Inspired by ebswift, https://www.ebswift.com/reverse-engineering-spl-usb.html

# The Wensn WS1381 answers these bRequests
# 1 seems to be constant - array of 2 bytes returned
# 2 readMode - array of 1 byte returned
# 3 setMode - array of 1 byte returned
# 4 read SPL - array of 2 bytes returned
# 82 array of 4 bytes returned

ranges = ["30-80", "40-90", "50-100", "60-110", "70-120", "80-130", "30-130"]
speeds = ["fast", "slow"]
weights = ["A", "C"]
maxModes = ["instant", "max"]

def connect():
    dev = usb.core.find(idVendor=0x16c0, idProduct=0x5dc)
    assert dev is not None, "Is your sound meter plugged in to USB?"
    print(dev)
    return dev

def readBRequest(dev, bRequest):
    ret = dev.ctrl_transfer(0xC0, bRequest, 0, 10, 200)
    print(ret),
    for elem in ret:
        print(format(elem, '#010b')),
    print

def readMode(dev):
    ret = dev.ctrl_transfer(0xC0, 2, 0, 10, 200)
    #print(ret)
    #print(format(ret[0], '#010b'))

    rangeN = (ret[0]&7) # bits 1,2,3 in ret[0] return rangeN from 0 to 6
    weightN = (ret[0]&8)>>3 # bit 3 in ret[0] returns weight
    speedN = (ret[0]&16)>>4 # bit 4 in ret[0] returns speed
    maxModeN = (ret[0]&32)>>5 # bit 5 in ret[0] returns maxMode

    return(ranges[rangeN], weights[weightN],
           speeds[speedN], maxModes[maxModeN])

def setMode(dev, range="30-130", speed="slow", weight="A", maxMode="instant"):
    rangeN = ranges.index(range)
    speedN = speeds.index(speed)
    weightN = weights.index(weight)
    maxModeN = maxModes.index(maxMode)

    print("setMode: range:%s weight:%s speed:%s maxMode:%s" %
          (range, weight, speed, maxMode))
    wvalue = rangeN | (weightN&1)<<3 | (speedN&1)<<4 | (maxModeN&1)<<5
    # Function of bits 6 and 7 is unknown (nothing?)

    dev.ctrl_transfer(0xC0, 3, wvalue, 0, 200)

peak = 0
def readSPL(dev):
    global peak

    ret = dev.ctrl_transfer(0xC0, 4, 0, 10, 200) # wvalue (3rd arg) is ignored
    #print(ret)
    #print(format(ret[1], '#010b'))

    rangeN = (ret[1]&28)>>2 # bits 2,3,4 in ret[1] return rangeN from 0 to 6
    weightN = (ret[1]&32)>>5 # bit 5 in ret[1] return weightN
    speedN = (ret[1]&64)>>6 # bit 6 in ret[1] return speedN
    # bit 7 seems to alternate every 1 second?

    dB = (ret[0] + ((ret[1] & 3) * 256)) * 0.1 + 30
    if dB > peak:
        peak = dB
    return(dB, ranges[rangeN], weights[weightN], speeds[speedN])


if __name__ == "__main__":
    import logroll
    import datetime
    import time

    # connect to WS1381 over USB
    dev = connect()

    # set default modes: range="30-130", speed="slow", weight="A", maxMode="instant"
    setMode(dev)

    log = logroll.LogRoll(logdir="logs")
    while True:
        now = datetime.datetime.now()
        # roll over to a new log whenever the filename changes - in this case, every hour.
        log.open_or_reopen(now.strftime('%Y-%m-%d-%H-%M.log'))

        dB, range, weight, speed = readSPL(dev)
        print("%.2f,%s,%s,%s"
              % (dB, weight, speed, now.strftime('%Y,%m,%d,%H,%M,%S')),
              file = log.fp)
        print("%.2f,%s,%s,%s"
              % (dB, weight, speed, now.strftime('%Y,%m,%d,%H,%M,%S')))

        log.fp.flush()
        time.sleep(1)