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Electrical Design

Explained

This design uses the Texas Instruments TS721 circuit for the M-bus to TTL conversion. From here, the 3.3V TTL signal is taken to the ESP-12 / ESP8266 for further processing and reporting over WiFi to MQTT. Really, this hardware is agnostic to what you choose to report to, the HAN library will help you decode the serial signal into readable meter values.

An addition to this design is using a DS18B20 as a temperature sensor. Just a little added value in monitoring the temperature of your fuse box.

There is an on-board programming option for the ESP. In order to do programming, my experience is that you'll be better off disconnecting the RX/TX from the TSS721, so there's two jumpers for this.

Other than this, it's all about software. You can find the Arduino code to decode the HAN data and report the values over WiFi to an MQTT server.

Schematics

Schematics

PCB

PCB

Layers

Top Copper Bottom Copper Silk Combined
Top Copper Layer Bottom Copper Layer Silk Layer Combined Layer

Source Code

The full KiCad source for these design files are here in this folder. Download this repository, start KiCad, chose open project and select HAN_ESP_TSS721.pro to get going.

Component list

Name Value Part Comments
C1 220uF / 16V UVR1C221MED1TA Electrolytic Capacitor
C2 100nF / 63V R82EC3100AA70J Metal Film Capasitor
C3 100nF / 63V R82EC3100AA70J Metal Film Capasitor
C4 220uF / 16V UVR1C221MED1TA Electrolytic Capacitor
C5 220uF / 16V UVR1C221MED1TA Electrolytic Capacitor
C6 100nF / 63V R82EC3100AA70J Metal Film Capasitor
R1 22k CF14JT22K0 0.25W resistor
R2 470R CF14JT470R 0.25W resistor
R3 10k CF14JT10K0 0.25W resistor
R4 10k CF14JT10K0 0.25W resistor
R5 10k CF14JT10K0 0.25W resistor
R6 10k CF14JT10K0 0.25W resistor
R7 10k CF14JT10K0 0.25W resistor
R8 220R CF14JT220R 0.25W resistor
R9 220R CF14JT220R 0.25W resistor
R10 22k CF14JT22K0 0.25W resistor
R11 4k7 CF14JT4K70 0.25W resistor
U1 TSS721 TSS721AD M-bus tranciever
U2 ESP12-E ESP12 ESP8266 SMT MODULE (Check e-bay for this one)
U3 LM1117-3.3 LD1117AS33TR 3.3V Voltage regulator
U4 DS18B20 DS18B20 Maxim Temp Sensor
Q1 BSS84 BSS84PH6433XTMA1 P-FET transistor
J1 RJ45 54601-908WPLF RJ45 port
J2 uUSB 10118194-0001LF USB micro socket
J3 6-pin female header 4320-01074-0 6-pin female header
JP1 XG8S-0241 Jumper header
JP2 XG8S-0241 Jumper header
SW1 Tactile Switch 1825910-6 Tactile Button
SW2 Tactile Switch 1825910-6 Tactile Button
NONAME STC02SYAN Unless you have these lying in your drawer, you'll need two

Complete shoppingcart, ready to order: http://www.digikey.no/short/jj1vhv