CHESTER Current

This article describes the core functionality, hardware description, default configuration, example JSON message, and channel calibration of the catalog application CHESTER Current.

caution

Some of the basics are not provided, as they are common for all CHESTER catalog applications. Please see:

Getting started on how to connect device to Cloud.
Common functionality to know how LED, button and network configuration works.
Platform Management on how to work with the interactive console.

Application Overview

The application primarily targets non-invasive current measuring using the so-called DC Current "Transformer" (DCCT). It can measure up to 4 channels of both AC and DC currents. The current probes are clips around the measured line, which convert the magnetic flux (proportional to the electrical current) to a differential output voltage.

tip

The current probes require a 5 V power supply (generated using the boost converter on CHESTER-K1) during the measurement cycle. The boost converter and the power rails to each channel are software-controlled, so CHESTER Current can operate as a low-power device powered by the battery. Of course, the measurement interval plays a key role in the battery lifespan.

Apart from the current measurements, the device can be configured (on demand) to measure up to 4 voltage channels (in single-ended mode). It can combine both current and voltage measurements (the total number of channels never exceeds number 4).

Application Variants

CHESTER Current can be ordered in one of these variants:

CHESTER Current

The catalog CHESTER Current hardware consists of the following ordering codes:

CHESTER-M-CGLS - Standard mainboard
CHESTER-K1-C1-C2-C3-C4 - 4x Diff. Input + 5 V Boost
CHESTER-E2-LP - Enclosure with SMA pigtail

See Ordering Codes for more details.

Firmware build shield options: ctr_k1 ctr_lte

CHESTER Current Z

The catalog CHESTER Current Z hardware consists of the following ordering codes:

CHESTER-M-CGLS - Standard mainboard
CHESTER-K1-C1-C2-C3-C4 - 4x Diff. Input + 5 V Boost
CHESTER-Z1 - Backup module
CHESTER-E2-LP - Enclosure with SMA pigtail

See Ordering Codes for more details.

Firmware build shield options: ctr_k1 ctr_lte ctr_z

CHESTER Current 1W

The catalog application CHESTER Current 1W supports multiple external DS18B20 1-Wire temperature sensors.

The hardware of this application consists of the following ordering codes:

CHESTER-M-CGLS - Standard mainboard
CHESTER-K1-C1-C2-C3-C4 - 4x Diff. Input + 5 V Boost
CHESTER-E2-LP - Enclosure with SMA pigtail

See Ordering Codes for more details.

Firmware build shield options: ctr_ds18b20 ctr_k1 ctr_lte

Probes

You can choose up to 4 current probes with the following current ranges:

Maximum current 10 A
Maximum current 100 A
Maximum current 300 A
Maximum current 1.000 A
Maximum current 1.500 A

caution

The current range is specified for the DC. If you design your system for the AC, you have to multiply the maximum expected AC by the coefficient of 1.42 (square root of two) to see if the current probe fits within the limit.

Application Behavior

For the wiring diagram to CHESTER Current, please follow the terminal block description of the CHESTER-K1 extension module. The extension module CHESTER-K1 use both slots A and B. So you use the corresponding terminals A1 to A8 and B1 to B8.

Analog

The analog readings are sampled periodically (parameter channel-interval-sample). These readings are stored as a buffer of samples.
The collected samples are aggregated periodically (parameter channel-interval-aggreg). The minimum, maximum, average, and median aggregates are computed from the buffered samples. These aggregated results are referred to as measurements.
Each measurement has an associated timestamp. The buffer measurements are transferred as time-series data regularly (parameter interval-report).

Backup

CHESTER Current Z (equipped with CHESTER-Z1) can also report information on the backup battery and external DC power state.

The current battery voltage and external DC voltage are sent in every report.
When the DC power input changes, the timestamp of the change event is stored altogether with the connected/disconnected state, this information is buffered, and the buffer of the events is sent (at the latest) with the regular report (parameter interval-report).
Optionally, DC power input changes to the connected (parameter backup-report-connected) or disconnected (parameter backup-report-disconnected) states can be reported immediately or with a configurable delay (parameter event-report-delay) to allow capturing multiple consequent input changes.
The maximum number of reports per hour is configurable (parameter event-report-rate). The event throttling limits communication bandwidth and preserves the battery lifespan.

caution

The next report interval is calculated at the beginning of the transmission cycle as the interval-report parameter (specified in seconds) ±20 % spread. This spread is intentionally random to avoid transmission aliasing for multiple devices operating in the same place (e.g., powered from a local DC line). If such a spread was not implemented, the device transmission could synchronously overlap.

Default Configuration

This is the default configuration (printed using the app config show command):

app config interval-report 900
app config event-report-delay 1
app config event-report-rate 30
app config backup-report-connected true
app config backup-report-disconnected true
app config channel-interval-sample 60
app config channel-interval-aggreg 300
app config channel-active 1 false
app config channel-active 2 false
app config channel-active 3 false
app config channel-active 4 false
app config channel-differential 1 false
app config channel-differential 2 false
app config channel-differential 3 false
app config channel-differential 4 false
app config channel-calib-x0 1 0
app config channel-calib-x0 2 0
app config channel-calib-x0 3 0
app config channel-calib-x0 4 0
app config channel-calib-y0 1 0
app config channel-calib-y0 2 0
app config channel-calib-y0 3 0
app config channel-calib-y0 4 0
app config channel-calib-x1 1 0
app config channel-calib-x1 2 0
app config channel-calib-x1 3 0
app config channel-calib-x1 4 0
app config channel-calib-y1 1 0
app config channel-calib-y1 2 0
app config channel-calib-y1 3 0
app config channel-calib-y1 4 0
app config channel-calib-mode 1 rms
app config channel-calib-mode 2 rms
app config channel-calib-mode 3 rms
app config channel-calib-mode 4 rms
app config w1-therm-interval-sample 60
app config w1-therm-interval-aggreg 300

Specific Commands

info

You can easily explore the whole command tree structure - start with the help command.

Commands

Command to trigger sample immediately (and store the result in the sample buffer):

sample

Command to send data immediately (and flush the aggregated measurements):

send

Reporting

Use this command to set report interval (in seconds):

app config interval-report <value>

Backup

Use this command to configure a short delay (in seconds) between the backup event and its reporting:

app config event-report-delay <value>

tip

This feature is useful in systems where another change may arrive shortly after the first one.

Use this command to limit the number of asynchronous backup event reports in a one-hour window:

app config event-report-rate <value>

tip

This feature helps to conserve power in the battery-operated device and optimizes the amount of transferred data. The regular (periodic) reports set by the parameter interval-report are not counted to this limit.

Use these commands to enable/disable reporting of the backup module power input connect/disconnect events:

app config backup-report-connected <true/false>
app config backup-report-disconnected <true/false>

Analog Channels

Command to enable/disable channel n (index 1-4):

app config channel-active <n> <true/false>

Command to switch between single-ended/differential modes on the channel n (index 1-4):

app config channel-differential <n> <true/false>

Command to set calibration point X0 (input) on the channel n (index 1-4):

app config channel-calib-x0 <n> <value>

Command to set calibration point Y0 (output) on the channel n (index 1-4):

app config channel-calib-y0 <n> <value>

Command to set calibration point X1 (input) on the channel n (index 1-4):

app config channel-calib-x1 <n> <value>

Command to set calibration point Y1 (output) on the channel n (index 1-4):

app config channel-calib-y1 <n> <value>

Command to set calibration mode on the channel n (index 1-4):

app config channel-calib-mode <n> <avg/rms>

Mode	Description	Use Case
`avg`	Mean (average) value	DC signals, slow-changing values
`rms`	Root Mean Square	AC signals, current transformers

Channel Commands

The following shell commands allow interactive calibration and reading of channels:

Command	Description
`channel <n> read`	Read raw and calibrated values
`channel <n> calib set-0 <value>`	Set calibration point 0
`channel <n> calib set-1 <value>`	Set calibration point 1
`channel <n> calib show`	Show calibration parameters
`channel <n> calib reset`	Reset calibration to defaults
`channel <n> calib mode [avg\|rms]`	Get/set calibration mode

Where <n> is channel number 1-4.

1-Wire Thermometer

Command to set 1-Wire thermometer sample interval in seconds:

app config w1-therm-interval-sample <1-86400>

Command to set 1-Wire thermometer aggregate interval in seconds:

app config w1-therm-interval-aggreg <1-86400>

Firmware

The latest firmware is available in Catalog Applications Firmware chapter.

Firmware v3.5.1

Variant	Version	Link
CHESTER Current	v3.5.1	Download
CHESTER Current Z	v3.5.1	Download

Example JSON Message

LTE
LoRaWAN

{
  "message": {
    "version": 1,
    "sequence": 42,
    "timestamp": 1738627200
  },
  "system": {
    "uptime": 86400,
    "voltage_rest": 3.65,
    "voltage_load": 3.42,
    "current_load": 28
  },
  "network": {
    "parameter": {
      "eest": 7,
      "ecl": 0,
      "rsrp": -89,
      "rsrq": -10,
      "snr": 12,
      "plmn": 23003,
      "cid": 1234567,
      "band": 20,
      "earfcn": 6300
    }
  },
  "thermometer": {
    "temperature": 23.45
  },
  "accelerometer": {
    "accel_x": 0.012,
    "accel_y": -0.008,
    "accel_z": 1.002,
    "orientation": 2
  },
  "analog_channels": [
    {
      "channel": 1,
      "raw_rms": {
        "measurements": [
          { "timestamp": 1738627200, "period": 300 },
          { "min": 70.12, "max": 72.45, "avg": 71.28, "mdn": 71.30 },
          { "min": 69.88, "max": 73.01, "avg": 71.45, "mdn": 71.42 }
        ]
      },
      "raw_mean": {
        "measurements": [
          { "timestamp": 1738627200, "period": 300 },
          { "min": 49.50, "max": 51.20, "avg": 50.35, "mdn": 50.32 },
          { "min": 49.22, "max": 51.55, "avg": 50.38, "mdn": 50.40 }
        ]
      },
      "calibration": {
        "mode": 1,
        "measurements": [
          { "timestamp": 1738627200, "period": 300 },
          { "min": 9.85, "max": 10.18, "avg": 10.01, "mdn": 10.02 },
          { "min": 9.82, "max": 10.25, "avg": 10.03, "mdn": 10.04 }
        ]
      }
    }
  ]
}

info

The payload structure for analog channels has changed in v3.5.1:

raw_rms - Contains RMS measurements in mV
raw_mean - Contains mean (average) measurements in mV
calibration - Contains calibrated values based on the selected mode (0=avg, 1=rms)

CHESTER Current supports binary LoRaWAN payload encoding. Example with battery + thermometer + channel 1 active:

Header: 0x25 0x00 (bits: BATT=1, ACCEL=0, THERM=1, W1=0, BACKUP=0, CH1=1)

Raw bytes (hex):

25 00 45 0E 5A 0D 1C 29 09 00 47 00 48 E4 49

Decoded:

Offset	Bytes	Field	Value
0-1	`25 00`	Header	0x0025 (BATT + THERM + CH1)
2-3	`45 0E`	voltage_rest	3653 mV
4-5	`5A 0D`	voltage_load	3418 mV
6	`1C`	current_load	28 mA
7-8	`29 09`	temperature	23.45 °C (2345 / 100)
9-10	`00 47`	ch1_rms	71.5 mV (float16)
11-12	`00 48`	ch1_mean	50.3 mV (float16)
13-14	`E4 49`	ch1_calib	10.02 A (float16)

Total: 15 bytes

Channel Calibration

danger

When upgrading firmware from v1.x.x to version v2.0.0 and newer - it is necessary to backup configuration. In the case of using CHESTER Current also calibration data.

caution

The following section is provided only for reference. Usually, the CHESTER Current devices are ordered altogether with the current probes, and HARDWARIO does the channel calibration for their customers in such a case.

Calibration System Overview

The calibration system uses two-point linear interpolation to convert raw mV readings to calibrated values (e.g., Amps, Watts, or any physical unit).

tip

Linear interpolation is defined by this formula for output calculation:

calibrated = (y0 × (x1 - raw) + y1 × (raw - x0)) / (x1 - x0)

Where:

x0, x1 = Raw mV values at calibration points
y0, y1 = Real physical values at calibration points
raw = Current raw mV reading

Configuration Parameters

Parameter	Type	Range	Default	Description
`channel-active-1..4`	bool	true/false	false	Enable channel
`channel-differential-1..4`	bool	true/false	true	Differential mode
`channel-calib-x0-1..4`	float	-10000..10000	0	Raw mV at point 0
`channel-calib-x1-1..4`	float	-10000..10000	0	Raw mV at point 1
`channel-calib-y0-1..4`	float	-10000..10000	0	Real value at point 0
`channel-calib-y1-1..4`	float	-10000..10000	0	Real value at point 1
`channel-calib-mode-1..4`	enum	avg/rms	rms	Calibration mode

Calibration Procedure

Prerequisites

Connect the current sensor (e.g., CT clamp) to the CHESTER-K1 channel
Connect to CHESTER via RTT shell or USB console
Have a reference measurement device ready (multimeter, clamp meter)

Step-by-Step Calibration

1. Enable the Channel

app config channel-active-1 true

2. Set Calibration Mode

Choose rms for AC current transformers or avg for DC sensors:

channel 1 calib mode rms

3. Verify Raw Reading

Read the current raw mV value:

channel 1 read

Output example:

Channel 1: avg=0.5 rms=1.2 mV (mode=rms, no calibration)

4. Calibration Point 0 (Zero/Low Point)

Apply a known low current (e.g., 0 A) and set the calibration:

channel 1 calib set-0 0

This captures the current raw mV reading as x0 and sets y0 = 0.

Output:

Channel 1: avg=0.5 rms=1.2 (using rms), point 0 set (x0=1.20, y0=0.00)

5. Calibration Point 1 (High Point)

Apply a known high current (e.g., 10 A) and set the calibration:

channel 1 calib set-1 10

This captures the current raw mV reading as x1 and sets y1 = 10.

Output:

Channel 1: avg=50.3 rms=71.5 (using rms), point 1 set (x1=71.50, y1=10.00)

6. Verify Calibration

Read the channel to see calibrated output:

channel 1 read

Output:

Channel 1: avg=50.3 rms=71.5 mV (mode=rms, calibrated: 10.00)

7. Show Calibration Parameters

channel 1 calib show

Output:

Channel 1 calibration: x0=1.20 y0=0.00, x1=71.50 y1=10.00, mode=rms

Reset Calibration

To clear calibration and return to raw mV output:

channel 1 calib reset

Legacy Calibration Method

In HARDWARIO, we have a calibration kit for CHESTER Current made of several air-core coils with 10/50/100 turns.

Example Current Calibration (Legacy)

Measure the zero-current offsets and write them for each channel as the x0 parameter

tip
Use the sample command to trigger the measurement.
Let's assume calibration of 100 A current probe and pick the 100-turn coil.
Set the laboratory power supply's current limit to 900 mA, and connect the power supply to the coil.
Clip the current probe around the calibration coil.
Verify the current flowing to the coil using a multimeter connected in series.
Measure the channel, and write the reading as the x1 value.
Set the y1 parameter to the value 90000.

info
The value represents the multiplication of the number of turns on the coil and the power supply's current limit - in this example 90000.
Since we assumed a zero-current offset point, we can keep the x0 parameter set as 0.
Save the configuration data (using the config save command) and verify the applied calibrated values.

Changelog

v3.5.0 — 2025-12-03

Added: New variants — CHESTER Current Z (with CHESTER-Z1 backup module) and CHESTER Current 1W (with external DS18B20 1-Wire temperature sensors)
Added: LoRaWAN support — single firmware binary for both LTE and LoRaWAN; mode selectable via app config mode lte / app config mode lrw
Changed: Cloud v2 protocol adopted (CBOR encoding, new API endpoints); previous Cloud v1 firmware remains separately available

Application Overview​

Application Variants​

CHESTER Current​

CHESTER Current Z​

CHESTER Current 1W​

Probes​

Application Behavior​

Analog​

Backup​

Default Configuration​

Specific Commands​

Commands​

Reporting​

Backup​

Analog Channels​

Channel Commands​

1-Wire Thermometer​

Firmware​

Firmware v3.5.1​

Example JSON Message​

Channel Calibration​

Calibration System Overview​

Configuration Parameters​

Calibration Procedure​

Prerequisites​

Step-by-Step Calibration​

1. Enable the Channel​

2. Set Calibration Mode​

3. Verify Raw Reading​

4. Calibration Point 0 (Zero/Low Point)​

5. Calibration Point 1 (High Point)​

6. Verify Calibration​

7. Show Calibration Parameters​

Reset Calibration​

Legacy Calibration Method​

Example Current Calibration (Legacy)​

Changelog​

v3.5.0 — 2025-12-03​

Application Overview

Application Variants

CHESTER Current

CHESTER Current Z

CHESTER Current 1W

Probes

Application Behavior

Analog

Backup

Default Configuration

Specific Commands

Commands

Reporting

Backup

Analog Channels

Channel Commands

1-Wire Thermometer

Firmware

Firmware v3.5.1

Example JSON Message

Channel Calibration

Calibration System Overview

Configuration Parameters

Calibration Procedure

Prerequisites

Step-by-Step Calibration

1. Enable the Channel

2. Set Calibration Mode

3. Verify Raw Reading

4. Calibration Point 0 (Zero/Low Point)

5. Calibration Point 1 (High Point)

6. Verify Calibration

7. Show Calibration Parameters

Reset Calibration

Legacy Calibration Method

Example Current Calibration (Legacy)

Changelog

v3.5.0 — 2025-12-03