This repository documents how to read live USB measurements of wind speed, temperature, and relative humidity from a MASTECH MS6252B digital anemometer in Processing/Java and Python:
To the best of our knowledge, the data streams produced by the MS6252B have not been documented by the manufacturer or elsewhere. The information presented here was obtained by reverse-engineering the data streamed by the device.
The MASTECH MS6252B, about $100, is a handheld digital anemometer with a mode for providing real-time data over USB. According to the user manual (3MB PDF), it can measure wind speed, ambient temperature, relative humidity, air volume, dew point temperature, and wet bulb temperature. The front-panel controls provide unit switching, minimum/maximum readings, temperature mode selection, and the toggling of USB data transmission. The meter can be handheld or mounted for fixed measurements, and it runs from a single 9V battery.
This repository focuses on acquiring the live USB stream: enabling USB mode on the meter, decoding the binary serial packets, and using the readings within Processing/Java or plain Python command-line tools. This project provides code for acquiring wind speed, ambient temperature, and relative humidity, but does not yet support acquisition of air volume, dew point temperature, or wet bulb temperature measurements.
The MS6252B does not always stream data just because the cable is connected. The meter has a USB real-time uploading mode that must be enabled from the front panel.
From the user manual:
- Power on the meter.
- Connect the meter to the computer with a USB cable.
- Long-press the backlight / USB key for about 3 seconds.
- Confirm that the
USBindicator appears on the LCD.
The relevant button is labeled with the backlight symbol and USB. In the
manual's button description, this is the backlight / USB real-time data
uploading button.
Long-pressing the same key again for about 3 seconds disables USB real-time
uploading. If the serial port exists but no bytes are arriving, check that the
USB indicator is visible on the meter display.
The MS6252B's observed working UART settings are 9600-8-N-1, i.e.,
9600 baud
8 data bits
no parity
1 stop bit
no flow control
The meter exposes a Silicon Labs CP210x USB-to-UART bridge. On macOS it appears
as a serial device like (e.g) /dev/cu.usbserial-0001. On Linux / Raspberry Pi it appears as something like: /dev/ttyUSB0
The meter's data stream is binary, not ASCII text. Opening it in a terminal program such as picocom will show unintelligible characters even when the serial settings are
correct. This is because values such as 0x01, 0x03, 0x92, and 0xA1
are control or non-printable bytes, so terminal programs render them as odd
symbols or replacement characters. That does not mean the baud rate is wrong.
For this meter, a repeating 13-byte binary pattern at 9600-8-N-1 is the useful
signal.
The meter sends a repeating 13-byte packet with the following format:
SS 01 RH_HI RH_LO 00 00 T_HI T_LO 01 01 W_HI W_LO 03
The packet contains relative humidity, temperature, and wind speed. Based on our observations, these are the bytes:
| Byte index | Name | Meaning |
|---|---|---|
| 0 | SS |
Status / mode byte; observed as 0x00 and 0x01 |
| 1 | 0x01 |
Constant header byte |
| 2 | RH_HI |
Relative humidity high byte |
| 3 | RH_LO |
Relative humidity low byte |
| 4 | 0x00 |
Constant separator / unknown field |
| 5 | 0x00 |
Constant separator / unknown field |
| 6 | T_HI |
Temperature high byte |
| 7 | T_LO |
Temperature low byte |
| 8 | 0x01 |
Constant separator / unknown field |
| 9 | 0x01 |
Constant separator / unknown field |
| 10 | W_HI |
Wind speed high byte |
| 11 | W_LO |
Wind speed low byte |
| 12 | 0x03 |
Frame terminator |
The most useful way to synchronize is to buffer bytes until you receive 0x03, and then look back 13 bytes and validate the constant positions. For example, the Processing/Java parser checks:
frame[1] == 0x01
frame[2] == 0x01
frame[4] == 0x00
frame[5] == 0x00
frame[8] == 0x01
frame[9] == 0x01
frame[12] == 0x03
This project assumes that the device has been configured to produce metric measurements of relative humidity, temperature, and wind speed; other configurations are not currently supported. All three measurements are encoded as big-endian 16-bit integers.
Relative humidity (%):
RH_percent = uint16_be(RH_HI, RH_LO) / 10.0
Temperature (°C):
temperature_C = int16_be(T_HI, T_LO) / 10.0
Wind speed (m/s):
wind_m_per_s = uint16_be(W_HI, W_LO) / 100.0
In Processing / Java:
int unsigned16(int highByte, int lowByte) {
return ((highByte & 0xff) << 8) | (lowByte & 0xff);
}
int signed16(int highByte, int lowByte) {
int v = unsigned16(highByte, lowByte);
if ((v & 0x8000) != 0) {
v -= 0x10000;
}
return v;
}
float humidityPct = unsigned16(frame[2], frame[3]) / 10.0;
float temperatureC = signed16(frame[6], frame[7]) / 10.0;
float windSpeed = unsigned16(frame[10], frame[11]) / 100.0;Here's an example frame:
01 01 01 92 00 00 00 63 01 01 00 2A 03
Decoded:
RH = 0x0192 / 10 = 40.2 %
temperature = 0x0063 / 10 = 9.9 C
wind = 0x002A / 100 = 0.42 m/s
Another observed frame:
01 01 01 A1 00 00 00 68 01 01 00 55 03
Decoded:
RH = 0x01A1 / 10 = 41.7 %
temperature = 0x0068 / 10 = 10.4 C
wind = 0x0055 / 100 = 0.85 m/s
The first byte can vary with meter state. For example, this frame has SS = 0x00, but decodes the same way:
00 01 01 A6 00 00 00 F3 01 01 00 1C 03
Decoded:
RH = 0x01A6 / 10 = 42.2 %
temperature = 0x00F3 / 10 = 24.3 C
wind = 0x001C / 100 = 0.28 m/s
Wind speed is encoded as a big-endian unsigned 16-bit integer divided by 100.
rawWind = uint16_be(W_HI, W_LO)
displayed wind = rawWind / 100.0
The Processing sketch currently prints both rawWind and the last accepted
frame in hex, which is useful when checking any new range or unit setting.
The Processing/Java sketch is known to work with Processing v.4.5.1, and can be found here:
It automatically scans Serial.list() and prefers ports whose names contain:
usbserial
slab
cp210
The sketch plots wind speed and displays decoded wind speed, temperature, relative humidity, raw integer values, and the latest packet in hex.
Keyboard controls:
r reconnect serial port
m toggle mouse fallback if no serial value has been parsed
This repository also includes two Python command-line programs:
ms6252b_anemometer_python/ms6252b_readings.py— live terminal display of decoded readingsms6252b_anemometer_python/ms6252b_probe.py— raw serial capture / debugging probe
They use only the Python standard library; no pip install step is required.
Only one program can open the serial port at a time. Close Processing, serial monitors, or the other Python script before running one of these.
ms6252b_readings.py is the normal terminal program. It prints wind speed,
temperature, and relative humidity as new packets arrive.
On macOS:
python3 ms6252b_anemometer_python/ms6252b_readings.py /dev/cu.usbserial-0001On Linux / Raspberry Pi:
python3 ms6252b_anemometer_python/ms6252b_readings.py /dev/ttyUSB0Example output:
reading /dev/cu.usbserial-0001 at 9600-8N1; press Ctrl-C to stop
19:24:10 wind= 0.42 m/s temp= 9.9 C RH= 40.2%
19:24:11 wind= 0.85 m/s temp= 10.4 C RH= 41.7%
19:24:12 wind= 1.17 m/s temp= 10.2 C RH= 42.3%
Useful options:
python3 ms6252b_anemometer_python/ms6252b_readings.py /dev/cu.usbserial-0001 --raw
python3 ms6252b_anemometer_python/ms6252b_readings.py /dev/cu.usbserial-0001 --once--raw also prints each decoded 13-byte frame in hex. --once prints the next
valid reading and exits.
You can combine them:
python3 ms6252b_anemometer_python/ms6252b_readings.py /dev/cu.usbserial-0001 --once --rawms6252b_probe.py was used for debugging the serial stream. It captures bytes for a
fixed number of seconds, prints hex dumps, and shows any decoded frames.
On MacOS:
python3 ms6252b_anemometer_python/ms6252b_probe.py /dev/cu.usbserial-0001 --baud 9600 --mode 8N1 --seconds 5On Linux / Raspberry Pi:
python3 ms6252b_anemometer_python/ms6252b_probe.py /dev/ttyUSB0 --baud 9600 --mode 8N1 --seconds 5The probe prints:
- raw bytes as hex
- printable ASCII, mostly for confirming that the stream is not text
- decoded RH / temperature / wind frames
To scan several common UART settings:
python3 ms6252b_anemometer_python/ms6252b_probe.py /dev/cu.usbserial-0001 --scan --seconds 2