Can the Photon be powered by the Arduino Mega? The Photon and Mega will be exchanging data thru the tx/rx I hope, but I was wondering if the powering was possible so there is only one power supply to the project.
Sorry for any confusion, new to the Particle world.
Yes power it using 3.3v and ground, but to use tx/rx you will probably need to use a logic converter because the mega tx/rx is 5v while the photon is 3.3v.
So, from what I have read thru in these posts, if I connect Tx on the Mega to the Rx on the Photon and then the Rx to the Tx as well. Then GND from the Mega to the Photon.
I did try connecting the two together, but the nothing lit up on the Photon.
If you want to power the Photon from an Arduino Mega you may want to connect the 5V on the Mega to Vin on the Photon, GND to GND - not sure what the current rating of the 3.3V output of the Mega is, hence I’d rather go with the unregulated 5V.
The RX/TX connections won’t power the device.
However, depending on the one power supply you have, you may still be able to directly power both devices off of that one supply without needing to go through one device into the other.
Hence disclosing what kind of PSU you have may be helpful.
By using something like this?:
yes.
You should go to Vin not VBAT.
Thanks @ScruffR for the heads up. I had been reading all of the above mentioned post and there was a VBAT mentioned and probably subconsciously had the “V” on the brain I guess.
I’m going to connect things up today.
Using the settings advise of above worked just fine. I connected the DFRobot Mega to a computer via the USB cable and the Photon booted.
Now I need to get the App working correctly that will interface with the Photon and I’ll be off.
Thanks for all of the pointers.
The suggested solution is good, but I want to make sure to point out one thing again (@nrobinson2000 already pointed this out, but it's IMPORTANT! 
The TX Data output from your Mega will be at 5 volts, and that's higher than the 3.3v that your photon is running on, so you should put that through a level converter... at a minimum, use a 1k + 2 k resistor divider between MEGA TX output and Photon RX input. Otherwise, you could make your photon serial port "deaf".
The Mega should be able to differentiate the data with a 3.3v TX from the photon, because it's less than 5 volts, but it's more than "no mans land"... but if you are having trouble, get a real 3.3v to 5v level shifter, and put that on both lines.
See 3.3V to 5V level shifter for high speed serial - Project Guidance - Arduino Forum for a discussion on the topic
mega TX ------'\/\/\/`----+-----'\/\/\/`------- ground1k | 2k v to Photon RX
Always better safe than sorry, but just for the records all but A3 & A6 (aka DAC) on the Photon are 5V tolerant.
@Zonker thanks for the tip. Will add them.
In the Frizting sketch I upload in an above post, the smaller breadboard, is there any point in using it as a hub for the 5v and GND wires between all of the connecting devices? There are 4 different 7 segment device going to be connected to the Mega, plus the Photon.
