RC receiver 5VDC supply port other than J9 in flight core

[Anubhav]

Hi,

I wanted to know, can we give power to RC receiver from port other than J9 in flight core? I am asking this because of unavailability of 3 pin JST connector and we are using custom made RC input cable where 5VDC wire connected to 4 pin JST connector ( instead of 3 pin ) and GND, SBUS wire together in 4 pin JST connector which connects to yellow port in flight core.
So, my question is can we provide 5VDC to RC receiver from 4G LTE modem? If yes, which 4 pin port can we use J4 (upstream), J5 (downstream) or J6 (downstream) in 4G LTE modem?

Thanks!

[Anubhav]

I am sorry for tagging at wrong product this question is related to VOXL-CAM.

[Vinny]

@Anubhav Hi,
Yes, that 5V on J9 is shared on several other connectors.
If you review this page: https://docs.modalai.com/flight-core-datasheets-connectors/
and look for any connector that you are not using that has this description "5VDC" or "5VDC (other pins are 3.3V, input or output if supplied at another pin)" then they are all connected together.
For example, J5, J6, J7, J8, and J10 all have 5V on Pin 1, and DGND on all JST GH connectors on the last pin (i.e.: a 4-pin connector has DGND on pin 4, 6-pin has DGND on Pin 6, so-on).
Let us know if you need anything else.
Thanks!

[Anubhav]

Hi @Vinny,

We have tried giving 5VDC power through flight core J8 port and receiver is getting powered-on but it's not taking any command like arm / disarm or response from throttle.
But when we are connecting to LTE modem 4 pin port J5 or J6 it is taking command also. So, I just wanted to ask, Is it safe if we give 5VDC to receiver through LTE Modem port J5 or J6 port in VOXL-CAM? If yes, then which port J5 or J6?

Thanks!

[Vinny]

Hi @Anubhav , That's very odd that J8 is not working. It's a hard short to the 5V power subsystem that feeds the board. There is no limitation I can see that would prevent that.
I know for Spektrum based receivers, there is a specific 3.3V power sequence and bit-wiggling that occurs for binding (through Flight Core J12), so I'm not sure if your receiver is expecting something similar and does not like the "always on" 5V on M0018 J8 and J9.
The 4G LTE modem M0030 ports J5 and J6 are safe to use. They expose a 500mA limited 5V to those pins. They are USB2 ports @500ma, with USB HS data on pins 2/3, and DGND on Pin 4.
They are turned on sometime after power-on once the hub enumerates with Voxl, so I wonder if that delay ON time is what is helping your receiver bind and communicate properly.
You might be venturing into a Software domain which I am not an expert in, so if just knowing that J5 and J6 are "safe" and this works for you, then great!
If not, we may need to pull in some SW folks to dig deeper.
Thanks!
Vinny