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Heatpump Monitor Build

Please note: 100k / 10k blue resistors look very similar! When assembling be sure to use select the 10k resistor for the ACAC voltage divider input.

The heatpump monitor comes as a component kit with all the resistors, capacitors, connectors, IC's and other parts required to complete the build. The full Bill of Materials can be found here

Packaged Kit


Core kit components


MBUS Reader kit components


Resistor reference

The following resistors are included in the kit.

Quantity Resistance Colour code Function
8 470k (5%) Yellow-purple-yellow CT + ACAC Voltage dividers
1 120k (blue, 1%) Brown-red-black-orange ACAC voltage divider top
1 10k (blue, 1%) Brown-black-black-red ACAC voltage divider bottom
3 10k (5%) Brown-black-orange Mixed use
1 4.7k (5%) Yellow-purple-red DS18B20 Temperature sensing
1 100k (5%) Brown-black-yellow Pulse counting dropdown
1 100R (5%) Brown-black-brown LED current limiting resistor
1 5.6k (5%) Green-blue-red Serial 5V to 3.3V level converter
3 22R (1%) CT burden resistors OPTION 1 (1%)
3 100R (1%) CT burden resistors OPTION 2 (1%)

MBUS Reader kit resistors:

1 220k (5%) Red-red-yellow MBUS Reader
1 33k (5%) Orange-orange-orange MBUS Reader
1 39k (5%) Orange-purple-orange MBUS Reader
1 22k (5%) Red-red-orange MBUS Reader
1 3k3 (5%) Orange-orange-red MBUS Reader
1 82R (5%) Grey-red-black MBUS Reader
2 1k (5%) Brown-black-red MBUS Reader

Component values including resistor resistance and capacitor capacitance are printed on the PCB. See resistor color code graphic here to help with matching the resistors images/resistor-color-chart.jpg.

Several of the resistors only have a reference name printed, the following are all part of the CT sensor and ACAC sensor biasing circuits and are all 470k resistors (470k (yellow-purple-yellow) was historically choosen to increase battery lifespan in battery powered nodes - lower values down to around 10k could be choosen instead here for a more stable biasing voltage):

VDT: Voltage Divider Top (for AC-AC Voltage sensor)
VDB: Voltage Divider Bottom (for AC-AC Voltage sensor)
VDT1: Voltage Divider Top 1 (for CT sensor 1)
VDB1: Voltage Divider Bottom 1 (for CT sensor 1)
VDT2: Voltage Divider Top 2 (for CT sensor 2)
VDB2: Voltage Divider Bottom 2 (for CT sensor 2)
VDT3: Voltage Divider Top 3 (for CT sensor 3)
VDB3: Voltage Divider Bottom 3 (for CT sensor 3)

CT Burden resistors:

The included burden resistor is 100 Ohms, this provides a AC power measurement range of 0 - 5.4 kW. A smaller burden resistor can be used instead for larger measurement range at lower resolution, 22 Ohms would provide 0 - 24 kW range. See Building Blocks guide CT sensors - interfacing with arduino

Example calculation:

Max Power = (((VREF ÷ 2) ÷ Burden resistance) × CT turns) × 230V ÷ sqrt(2)
Max Power = (((3.3V ÷ 2) ÷ 100R) × 2000 turns) × 230V ÷ sqrt(2) 
Copy into calculator: (((3.3÷2)÷100)×2000)×230÷sqrt(2) 

Burden resistor PCB name reference:

BUR1: Burden resistor 1 (for CT sensor 1)
BUR2: Burden resistor 2 (for CT sensor 2)
BUR3: Burden resistor 3 (for CT sensor 3)

Capacitors: C11, C13, C12, C19 all 10uF

The following image can also be used as a reference of component locations.


Tip 1: It is usually easier to start by soldering the lower profile components first such as the resistors and to build up to the taller components.

Tip 2: Test that the ATmega328 part works first before soldering in the ESP8266 module so that any issues with the ATmega328 part can be isolated before adding the ESP WIFI part.

Check that the power supply voltages are all as expected before inserting the ATmega328 in the 28pin holder.

ESP8266 Supply capacitor: An additional 10uF may be required across the supply to the ESP8266 module. The ground is top-left and 3.3v top-right. Adding this capacitor solved an issue with the unit resetting regularly - indicating a power supply issue.

ESP CH_PD and GPIO15 Solder jumpers Both of these solder jumpers need to be connected with a small blob of solder for the ESP module to work.

Build Guide Images

Voltage check

At this point with the voltage regulator soldered in, mini USB and capacitors its possible to check that the board is producing 3.3V from the 5.0V USB supply. Use a multimeter and connect across GND and 3.3V on one of the DS18B20 temperature sensor inputs. Check that the voltage regulator is not getting warm.

Arduino Upload check

This is also a good point to check that its possible to upload firmware to the ATmega328 microcontroller. Place the ATmega328 in the 28pin chip holder temporarily and try uploading the Arduino ATmega328 firmware, follow the instructions below in the Uploading the ATmega328 Firmware.

Once happy that the components so far are all soldered correctly and that the board voltages are still correct and that its still possible to upload code to the Arduino ATmega328, the next step is to solder in the radio module and ESP8266 Wifi module.

Start by placing a small blob of solder on one of the pads on the board. Then place the module on the board and adjust into position heating up the soldered pad so that a holding connection is made at this one point. Triple check the positioning of the modules before soldering the rest of the pads.

MBUS resistor and transistor reference:

Finished article:

Optional enclosure kit:

Uploading Firware

The Heatpump monitor has two microcontrollers. Firmware for these must be loaded separately:

Uploading the ATmega328 Firmware

The default heatpump monitor firmware can be found here:

Use a USB to UART programmer connected to the 6-way UART header closest to the ATmega328 to upload this firmware using the Arduino IDE. Be sure to select "Uno" as the board type in the Arduino IDE.

If you're using the cable sold through the OpenEnergyMonitor Shop, the drivers for Windows and Mac can be downloaded here:

The Heatpump Monitor repository contains all the Arduino libraries required to compile the heatpump monitor firmware. Once the Ardunio IDE is installed it can be configured to use these libraries by going to: File > Preferences and setting the sketchbook location to HeatpumpMonitor/Firmware/Arduino (including the full path to your HeatpumpMonitor folder on your system).

Uploading the ESP8266 Firmware: EmonESP

The EmonESP ESP8266 Firmware and upload guide can be found here:

GPIO0 Jumper: Place a jumper across the GPIO0 header just left of the ESP8266 module to place the ESP8266 module in bootloader mode. Power cycle the board to reset the ESP8266 module. Once the firmware is uploaded remove the GPIO0 jumper so that the ESP8266 starts up without going into bootloader mode at the next power cycle.

TX Jumper: Place the second jumper across the TX header to link the Atmega micro to the ESP8266 module. Required for sending data on to emoncms via WIFI.

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