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document SDM120 connection

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King Kévin 2017-01-22 16:05:55 +01:00
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README.md
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@ -84,6 +84,27 @@ Connections 3xPZEM-004T <-> board:
Note: when connecting multiple meters one the same UART bus only keep one of the pull-up resistors (across all meters) on the TX pin (on the opto-coupler output), else the low level is not low enough for the micro-controller to correctly decode the signal.
SDM120
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This 1-phase 2-wire electricity meter provides an RS-485 interface using the ModBus RTU protocol.
For the 3-phase 4-wire power distribution installation I used 3 meters, one per phase.
They can be connected to the same RS-485 bus once individual addresses have been set.
The used meter IDs (aka. slave address) are hard coded in `main.c`
A UART to RS-485 converter is used to be able to communicate with the meters.
The SDM120 ModBus protocol document provide by Eastron specify the commands and registers, but the timing (important) is specified in the SDM630 ModBus protocol document.
Connections 3xSDM120 <-> board:
- VCC; +5V
- GND; ground
- DI; PB10, USART3_TX
- DE; PB1 (shared with RE since one is active low while the other is active high)
- RE; PB1 (shared with DE since one is active low while the other is active high)
- RO; PB11, USART3_RX
ESP8266
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