PoE module (ID 3848) and Arduino Ethernet shield

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nemecben
 
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PoE module (ID 3848) and Arduino Ethernet shield

Post by nemecben »

Hello,
I ordered the 3848 PoE module that fits nicely on the Arduino Ethernet shield. It's been working, but the RTD-100 and Thermocouple sensors seem a bit off. I checked board voltage and it's consistently low; round 4.7 or so. The POE module output is solid at 5.0v I'm no Electrical Engineer, but if I read the schematics correctly the output of the POEE module is connected to the Arduino VIN (through the Ethernet shield to the power headder). Then the Arduino's on board regulator does it's best to put 5v on the +5v bus but cannot do that with only 5v on the VIN bus. I can think of two options:
1) hack the POE to Ethernet Shield header connection so that the POE module output goes to the arduino +5V bus
2) convince the POE module to output maybe 6v using the cryptically documented P2, pin3. The Chinese data sheet just shows NC, but the Ethernet Shield 2 schematic shows a voltage divider between vout (R5) and gnd (R7) feeding pin 3. The low side resistor (R7) is not populated so pin3 is just tied to the POE vout. Before I let the smoke out of stuff I'd like to know if anyone else used the voltage divider to bias the POE module to output just a little higher voltage so that the arduino onboard regulator can output 5v. Alternatively, in my simple mind it seems I could open both R5 and R7 then attach the POE p2 pin3 to the arduino +5v bus. I think that would cause the POE output to regulate up until the +5V can get to 5v.

Thanks!

Ethernet Shield2 schematic:
https://www.arduino.cc/en/uploads/Main/ ... V2-sch.pdf

POE module info from arduino.cc, maybe a different POE module than sold here?
https://www.arduino.cc/en/uploads/Main/ ... asheet.pdf

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adafruit_support_mike
 
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Re: PoE module (ID 3848) and Arduino Ethernet shield

Post by adafruit_support_mike »

nemecben wrote:1) hack the POE to Ethernet Shield header connection so that the POE module output goes to the arduino +5V bus
That's the way to go, assuming you're getting 5V from the PoE module.

The Vin pin connects to the input side of the LT1117 voltage regulator, which needs at least 1.5V of headroom to operate: it needs at least 6.5V.

If you have an external power source less than 6.5V, you can connect it directly to an Arduino's 5V pin. The board's built-in power selection circuit will keep bad things from happening.

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