This message was posted on behalf of Intel Corporation
It's great that you are designing your custom board for Edison! I'll do my best to try to help you with the DCIN doubts.
This is what the DCIN description in the Edison Hardware Guide says:
"DCIN is a signal that indicates whether the Intel® Edison device is being powered from a battery or from an external power source. DCIN also sets the voltage level required on VSYS in order to boot. When DCIN is floating or tied to ground, the voltage on VSYS MUST rise from 2.5 to 3.5 V in 100 ms, otherwise the boot is aborted. When the boot is aborted, power must be cycled below 2.5 V. If DCIN is connected to VSYS, the Intel® Edison device will start to boot when VSYS is above 2.5 V for 100 ms."
So, the main purpose of the DCIN pin is to specify the voltage level the Edison will require to boot. The expansion boards for Edison have this pin connected to VSYS, so that would be my recommendation for you as well, connect the DCIN pin to VSYS in your design. Then, you will only have to power the Edison with a voltage in the range of 3.15V to 4.5V without any worries about the DCIN pin. That voltage could be supplied by the battery or the DC power supply.
Here you have the schematics of the Edison expansion boards in case you want to check them and also, the Edison Hardware Guide which describes the DCIN functionality:
- Schematics for the Intel® Edison Board for Arduino*
- Schematics for the Intel® Edison Breakout Board
- Hardware Guide for the Intel® Edison Compute Module
Additionally, I find your design description very similar to the battery block from SparkFun. I recommend you to take a look at its schematic: https://cdn.sparkfun.com/datasheets/Dev/Edison/SFE_Battery_Block.pdf. You will see that there is a little circuit that allows the Edison to be powered from a rechargeable battery and also from a DC power supply, in this case a USB power supply. I believe you will find it very useful and you could adapt it to your specific requirements.
I hope I have clarified your doubts.
Have a nice day!