document SDM120 connection
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README.md
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README.md
@ -84,6 +84,27 @@ Connections 3xPZEM-004T <-> board:
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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.
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SDM120
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------
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This 1-phase 2-wire electricity meter provides an RS-485 interface using the ModBus RTU protocol.
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For the 3-phase 4-wire power distribution installation I used 3 meters, one per phase.
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They can be connected to the same RS-485 bus once individual addresses have been set.
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The used meter IDs (aka. slave address) are hard coded in `main.c`
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A UART to RS-485 converter is used to be able to communicate with the meters.
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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.
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Connections 3xSDM120 <-> board:
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- VCC; +5V
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- GND; ground
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- DI; PB10, USART3_TX
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- DE; PB1 (shared with RE since one is active low while the other is active high)
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- RE; PB1 (shared with DE since one is active low while the other is active high)
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- RO; PB11, USART3_RX
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ESP8266
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-------
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