Ethernet remote device controller sensor circuit

The main purpose is to show here the circuit diagram and explain the software. We use a UDP application to send commands to the microcontroller. Those commands will then cause the microcontroller to switch on or off the relay. It think it will be possible to even implement TCP. The current UDP software is less than 3k bytes and that is not even half of the memory on an Atmega88. TCP would then allow us to control the device via a web browser. I have however not tried it yet.
Ethernet remote device controller sensor circuit - schematic

Here is the circuit diagram. Most of it is very straight forward and standard for the ENC28J60. The polarity of LED-B is important as it determines the duplex operation of the chip. Standard Half-duplex is what makes most sense for a device which will send and receive only rather little traffic. A relay can be connected to connector CONN3. Note the diode D1. It is not useless and it is not the wrong way round in the circuit diagram even though it looks like that. It is there for those who plan to connect a small 6V relay on that output. It protects the whole circuit against the possibly very high voltages which can be induced by the coil of a relay.

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