has this been tested with POE hats or any other existing hats?

I originally installed a 3 relay contactor hat, but quickly grew out of that. I had to upgrade the power supply (Mean Well MDR-60-5) to 60 watts which powers the Pi (bypassing the micro USB port), 16 relay contactors (not all used), 8 sensors, and 4 3.3v step down regulators. The Pi is not a very good power source, especially 3.3v. All the gear is mounted on C45 DIN rails to avoid breadboards. All wire junctions are screw down like the this hat. Also the LEDs were very helpful in debugging. The code and it's relationship to the GPIO is quite complex. Latency and hysteresis were an ongoing challenge. I wouldn't cover the LEDs with another hat.

According to diagram, the posts appear to be one way (diode) from the gpio head. can i send signal back to the pi from this breakout?

The diode is a led. Set the GPIO pin of your choice to output and the led will show the state of the output of that GPIO pin. Set the GPIO pin of your choice to input and the led will show the state of whatever is input to that GPIO pin.

What are the length and width of the connector that fits onto the 40-pin header? I want to see if it will fit through the slot in the top of my case.

This is not the answer I was looking for. I would like to see if I can use this breakout box with the cover installed on my Raspberry Pi case. It has a slot 55 mm long X 8 mm wide. Will the header connector fit through this slot?

ASIN	B08RDYDG6X
Best Sellers Rank	#107,448 in Computers & Accessories ( See Top 100 in Computers & Accessories ) #929 in Motherboards
Brand Name	HCDC
Colour	blue, red
Connector Type	Screw
Current Rating	3 Amps
Customer Reviews	4.7 out of 5 stars 318 Reviews
Item Dimensions W x H	6.5W x 2.8H Centimeters
Item Pitch	3.5 Millimeters
Manufacturer	Xiken Electronic Technology Co., Ltd.
Material	Koper, Nylon
Material Type	Koper, Nylon
Model Number	HD040
Mounting Type	PCB Mount
Number Of Contacts	20
Number Of Poles	40
Number of Positions	40
Pitch	3.5 Millimeters
Voltage	3.3 Volts

RPi GPIO Status LED & Terminal Block Breakout Board HAT for Raspberry Pi A+ 3A+ B+ 2B 3B 3B+ 4B

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