owonb35
Bluetooth Client for Owon B35 Multimeter for newer (post mid 2017) multimeters with the Semic CS7729CN-001 chip.
Older multimeters that use the Fortune Semiconductor FS9922 chip should use inflex/owon-b35.
The Owon B35 series of multimeters use Bluetooth Low Energy (BLE) to transmit readings to remote monitors such as smartphone apps. This Linux client allows to to caputure measurement data to you computer to record in a file or display on charting software such as gnuplot or KST.
Requirements
This client requires the Gattlib BLE library to be installed. Compiled packages are available to install without needing to compile.
Installation
Either download the compiled binary or the source code to compile your own.
Compiling is a simple make.
Usage
The client is designed to be a simple receiver of measurement data that outputs in formats that can be piped into other tools for processing or display.
owonb35 [-s|-S|-t|-T|-d] [-c|-j] [-n|-u|-m|-b|-k|-M] [-x] [-r] [-q] [-h|-V] [<device_address>]
Measurement collection
owonb35 -R <seconds per measurement> <number of measurements> [<device_address>]
Start offline measurement recording
Client for Owon B35/B35+/B35T+ digital multimeters using bluetooth.
-i Interactive remote control
-s Timestamp measurements in elapsed seconds from first reading
-S Timestamp measurements in Unix epoch seconds
-t Timestamp measurements in elapsed milliseconds from first reading
-T Timestamp measurements in Javascript epoch milliseconds
-d Timestamp measurements with ISO date/time
-c Comma separated values (CSV) output
-j JSON output
-n Scale measurements to nano units
-u Scale measurements to micro units
-m Scale measurements to milli units
-b Scale measurements to base units
-k Scale measurements to kilo units
-M Scale measurements to mega units
-x Output measurement value without units or type for use with feedgnuplot
-R Start offline measurement recording
-r Download offline measurement recording
-q Quiet - no status output
-h Display this help and exit
-V Display version and exit
<device_address> Address of Owon multimeter to connect
otherwise will connect to first meter found if not specified
Interactive controls:
s - Select
a - Auto
r - Range
l - Backlight
h - Hold
b - Turn off Bluetooth
d - Delta (Relative)
f - Fequency Hz/Duty
m - Min/Max
n - Normal display
You can provide an optional Bluetooth address for the specific multimeter to connect to or the client will otherwise scan for devices and connect to the first multimeter it finds. Scanning and connection can be a bit flaky at times. Note that only one client can connect to the multimeter at a time.
Measurments can be optionally timestamped in actual time or elapsed time since the first measurement was received. Timestamps can be in seconds, milliseconds, or date-time. Note that the multimeter transmits measurements approximately every 600ms.
Output format defaults to space seperated values but can also be output in Comma Seperated Values (CSV) or JSON formats. By default, the measurement unit is output but this can be disabled for feeding applications that can only handle numeric data.
By default, measurements are output in the same scale and resolution as displayed by the multimeter. When using autoranging, this can result in the measurement scale and resolution changing when the multimeter changes ranges. To avoid this, you can optionally lock the measurement scale. However, as the multimeter autoranges, it will change the resolution of the measurement value.
Interactive Mode
Specifying the -i option allows you to interactively control the multimeter remotely from the client. Using these controls, you can change the measurement range, switch between some functions, display min/max/relative/hold values, and turn the backligh on. The interactive controls correspond to the multimeter front panel buttons.
Offline Recording
The client can be used to initiate offline recording using the -R option. With this command, specify the measurement interval in seconds per measurement, and the number of measurements to record. The multimeter has the capacity to store up to 10,000 measurements.
Offline recorded measurements are downloaded using the -r option. Recorded measurements are replayed and output in the same way as realtime measurements. Timestamp, format and scale options can be used to control the measurement output.
Interfacing
The client is designed to inteface into other tools using the normal Unix pipe and redirection mechanisms.
Files
Measurement values can be written directly to file using redirects:
Write timestamped measurements in CSV format - owonb35 -c -d > measurements.txt
The tee command can be used to write measurement values to a file and also pipe them to another application.
owonb35 | tee measurements.txt | next_tool
gnuplot
gnuplot is a very flexible plotting program. The client can feed measurements to gnuplot in realtime using feedgnuplot.
owonb35 -s -x -b | feedgnuplot --domain --lines --stream --ymin 0 --ylabel 'Volts' --xlabel 'Seconds' --exit
It is best to lock the measurement unit and scale to prevent them jumping around if the multimeter autoranges during measurement. feedgnuplot doesn't handle non-numeric data in its input, so the output of measurement units need to be disabled. It also cannot handle measurements with less than one second resolution, which means that it can only display elapsed timestamps. Data written to file and loaded into gnuplot can display actual timestamps.
MQTT
MQTT is a publish/subscribe messaging system frequently used in Internet of Things networks. It allows clients to publish data onto a network for other clients to subscribe to. Data is usually published as single values or in JSON format.
Single value - omonb35 -x -b | mosquitto_pub -t voltage -l
JSON format - omonb35 -T -b -j | mosquitto_pub -t measurement -l
Protocol
The multimeter uses the Bluetooth Low Energy Generic Attributes (BLE GATT) to transmit measurements.
Realtime Measurements
Measurement data is output as a BLE notification with a 0xfff4 UUID. The packet consists of three uint16_t numbers.
The first number encodes the function, scale, and decimal places.
Overload 1 1 1
Decimal--------------------------------------
| |
DCmV 1 1 1 1 0 0 0 0 0 0 0 1 1 x x x f0 18
DCV 1 1 1 1 0 0 0 0 0 0 1 0 0 x x x f0 20
ACmV 1 1 1 1 0 0 0 0 0 1 0 1 1 x x x f0 58
ACV 1 1 1 1 0 0 0 0 0 1 1 0 0 x x x f0 60
DCuA 1 1 1 1 0 0 0 0 1 0 0 1 0 x x x f0 90
DCmA 1 1 1 1 0 0 0 0 1 0 0 1 1 x x x f0 98
DCA 1 1 1 1 0 0 0 0 1 0 1 0 0 x x x f0 a0
ACuA 1 1 1 1 0 0 0 0 1 1 0 1 0 x x x f0 d0
ACmA 1 1 1 1 0 0 0 0 1 1 0 1 1 x x x f0 d8
ACA 1 1 1 1 0 0 0 0 1 1 1 0 0 x x x f0 e0
Ohm 1 1 1 1 0 0 0 1 0 0 1 0 0 x x x f1 20
kOhm 1 1 1 1 0 0 0 1 0 0 1 0 1 x x x f1 28
MOhm 1 1 1 1 0 0 0 1 0 0 1 1 0 x x x f1 30
nF 1 1 1 1 0 0 0 1 0 1 0 0 1 x x x f1 48
uF 1 1 1 1 0 0 0 1 0 1 0 1 0 x x x f1 50
Hz 1 1 1 1 0 0 0 1 1 0 1 0 0 x x x f1 a0
Duty 1 1 1 1 0 0 0 1 1 1 1 0 0 x x x f1 e0
TempC 1 1 1 1 0 0 1 0 0 0 1 0 0 x x x f2 20
TempF 1 1 1 1 0 0 1 0 0 1 1 0 0 x x x f2 60
Diode 1 1 1 1 0 0 1 0 1 0 1 0 0 x x x f2 a0
Continuity 1 1 1 1 0 0 1 0 1 1 1 0 0 x x x f2 e0
hFE 1 1 1 1 0 0 1 1 0 0 1 0 0 x x x f3 20
+------+---+--------+-----+-----+
F 0 Function Scale Decimal
Function
0 0 0 0 - DCV
0 0 0 1 - ACV
0 0 1 0 - DCA
0 0 1 1 - ACA
0 1 0 0 - Ohm
0 1 0 1 - Cap
0 1 1 0 - Hz
0 1 1 1 - Duty
1 0 0 0 - TempC
1 0 0 1 - TempF
1 0 1 0 - Diode
1 0 1 1 - Continuity
1 1 0 0 - hFE
Scale
0 0 1 - nano (n)
0 1 0 - micro (u)
0 1 1 - milli (m)
1 0 0 - Unit
1 0 1 - kilo (k)
1 1 0 - mega (M)
Decimal Places
0 0 0 - 0
0 0 1 - 1
0 1 0 - 2
0 1 1 - 3
1 0 0 - 4
1 0 1 - 5
1 1 1 - Overload
The second number bit encodes the reading type.
Hold-----------------------\ 01/05 Autorange
Delta--------------------\ | 02/06 Autorange
Autorange--------------\ | | 04
Low Battery----------\ | | |
Min----------------\ | | | | 10
Max--------------\ | | | | | 20
| | | | | |
00000000 X X X X X X X X
8 4 2 1 8 4 2 1
The third number is the measurement digits as a signed magnitude binary number (msb is sign bit). It is converted to the floating point measurement value by using the number of decimal places as specified in the first number.
Interactive Commands
Interactive commands are sent by writing a uint16_t number to UUID 0xfff3.
0x0101 Select
0x0002 Auto
0x0102 Range
0x0003 Backlight
0x0103 Hold
0x0004 Bluetooth Off
0x0104 Relative
0x0105 Hz/Duty
0x0006 Normal
0x0106 Min/Max
Offline Recording
Starting
Offline recording is initiated by writing the current date and time, and then the measurement interval and count to UUID 0xfff1. Year of date is split into uint8_t numbers for century and decade/year.
Measurement interval and count are uint32_t numbers. The maximum number of measurements that can be recorded in 10,000.
2a:44:41:54:65:14:12:04:0e:11:07:1b:00:00:00:00
* D A T e [C][Y] [M][D][H][M][S]
2a:52:45:43:4f:72:64:2c:40:16:40:00:10:27:00:00
* R E C O r d , [Sec/Rding] [Count ]
Once recording has started, the multimeter will disconnect.
Downloading
The number of bytes of offline measurement record data available is obtained by the writing the following command and then reading the result from UUID 0xfff1.
2a:52:45:41:44:6c:65:6e:3f:00:00:00:00:00:00:00
* R E A D l e n ?
The result will be a buffer contain a uint32_t number of bytes available. This number represents the length of data plus a length counter. The number of measurements available is the (number of bytes/2) - 1.
The downloading of offline measurement data is trigger by writing the following command to UUID 0xfff1.
2a:52:45:41:44:31:3f:00:00:00:00:00:00:00:00:00
* R E A D 1 ?
The multimeter sends offline measurement record data using notifications with UUID 0xfff4. Data is sent in 20 byte packets. Int1 and Int3 correspond to the first and third numbers sent in the realtime measurement data above.
Start marker
ff:ff: ff:ff: ff:ff: ff:ff: ff:ff: ff:ff: ff:ff: ff:ff: ff:ff: ff:ff
Header packet
14:12: 04:0e: 0e:17: 18:00: 02:00 :00:00 :2a:00: 00:00: 19:f0: 09:0e
[C][Y] [M][D] [H][M] [S] [Interval ] [Byte count ] [Int1] [Int3]
Data packets
09:0e: 0a:0e: 0a:0e: 0a:0e: 0a:0e: 0b:0e: 0b:0e: 0b:0e: 0b:0e: 0b:0e
[Int3] [Int3] [Int3] [Int3] [Int3] [Int3] [Int3] [Int3] [Int3] [Int3]
More data packets as required......
Finish Marker
ff:ff: ff:ff: ff:ff: ff:ff: ff:ff: ff:ff: ff:ff: ff:ff: ff:ff: ff:ff
Once the data is downloaded, the mutimeter returns to sending realtime measurement data.