Request for Feedback: Gateway Shield Power Supply


#1

The gateway shield has been re-spun to include feedback from users, mainly that it include breakouts for both the Core/Photon and the BLE module itself.

However, we wanted to try and gather some feedback on the power supply. Here is a quick rundown of the current configuration:

  • There is a USB Micro connector on-board
  • This connector is hooked to an LDO, the same used on the Particle Core, capable of outputting 500mA. This can power both the Particle board in the socket as well as the BLE module, as long as it draws less then 500mA total
  • At the same time, the Particle device in the socket can provide 3V3 to the board which will power the BLE module

The thought is that the on-board power supply can power the BLE module for debugging or whatever when there is no Particle board in the socket. Also, if a Spark Core or Photon is on the socket, the on-board power supply can power both the Particle board and the BLE module.

But we are asking, what if there is a higher powered board, aka the Electron, in the socket? The on-board system can’t power it. However, power can be supplied to the Electron itself and the gateway shield will use the 3V3 of the Electron to power the BLE module. It will work fine, you will just need to hook power to the Electron.

Is this design acceptable? The idea is that it doesn’t make sense, from a cost and complexity standpoint, to try and power any possible device in the socket. Adding it to work for the Core/Photon is negligible. So is ok to power the board from the Electron if you choose to use one?

Feedback welcome!


#2

I haven’t been following along too much here, but will try to provide my thought. Generally, in designs that I’ve done and worked with, if power comes into the board, it should power everything on the board without added work. Now there could be configuration jumpers or switches to route power as needed. But any extra wires or supplies should be eliminated.

I guess I haven’t looked at the Electron enough, it sounds like it could be a power draw because of the cellular aspect. You know, I read about the Fono from Adafruit over this past weekend. I saw that they devices uses a LiPo and LiPo circuit to provide that needed boost power for the modular aspect. Perhaps the voltage regulation circuit on the gateway shield uses a Lipo/USB/power regulator. When the Electron is used, one much attach an added LiPo (if the same scheme workout) and when using Core or Photo just the USB power is sufficient.

-Tim


#3

@eric, IMO there are different power scenarios:

  1. All devices powered from the on-board USB/LDO
  2. Core/Photon/Electron powered via their USB connector (to do DFU/Serial)
  3. Bluz powered by Core/Photon/Electron and/or on-board supply (extra ?)

The question is how is firmware developed and flashed - OTA only, USB/DFU? How much 3.3v power is available after powering the Bluz (100ma - ??). The gateway board should be able to handle the above.

In scenarios 1 & 2, a Particle device is required for power. There is a possibility to disable the Photon/Electron(?) onboard supply from the Bluz for very low power operation. In that case, the Bluz is SOL. For LiPo operation, a proper charger/regulator is needed but if the gateway is expected to always be plugged in, the LDO is fine. Perhaps what’s needed is some use cases and then figure out how to best power the gateway! :smile:


#4

Good point about use cases. I had been assuming all along that people would simply power the device from a constant source and not use batteries. The gateway is really meant to be a central hub for other battery powered devices, but perhaps people could see using it with an Electron off battery power?

The USB/LDO is there if you wanted to power it without a Particle board. Really, can’t think of a decent use case for it, but wanted the option for people to power it standalone. For example, if someone just wants a local BLE network of devices that report to a central hub, they can use the gateway without a Particle board. Since this gateway isn’t really breadboardable, I wanted an easy way to power it.

The on-board BLE module can be programmed through the Particle board. Once you plug in a Core/Photon/Electron (with the proper sketch), the BLE module will connect to the cloud through them. So you can program it OTA. There is on-board SWD that can be used for programming, but don’t imagine many people will do that. Unlike the bluz board itself that has a JTAG shield, that wasn’t an option here so I just put it on the board.

Power of the BLE module is nearly negligible compared to the Particle board, it will draw around 10-20mA.

I agree with @Swieter about having everything on the board run from its power supply without extra added work. However, the Electron can draw up to 2A (I believe), and who is to say that there isn’t some higher powered version of it in the future? So to some degree, we can’t plan for everything.


#5

@eric, I think keeping things simple is first and foremost. So, the board is meant as a gateway and therefore really needs a Particle device to operate. That way, OTA to Bluz is supported. For power, I agree that the board should supply everything but if a Particle device is required, then it could supply the Bluz. This latter configuration is not my favorite. I do not believe the Electron will ever draw 2Amps, more like 800ma to 1000ma tops. With that in mind, I think you have to consider a few things when designing the gateway:

  1. If battery operation is supported, then there should be onboard USB and charging/monitoring. Alternatively, this could be done by stacking the new Particle power shield and have it provide power to the Bluz. This may be an issue when using the Electron.
  2. You may want to consider a VBAT supercap or battery for the onboard Particle RTC (what about Bluz?)
  3. If battery operation is not supported (onboard) then the onboard LTO should provide enough power for the worst case Particle device (Electron).

UPDATE: So it looks like the 2G Electron needs 2.2A peak current but 3G only needs 800ma peak as I thought.


#6

I would be very curious to hear if anyone wants to use the gateway with a battery. For WiFi, I don’t see it making a lot of sense. For cellular, I could see it being practical, but does anyone actually plan to use it this way?

I don’t want to overdesign this gateway shield when the fine folks at Particle are already solving a lot of these problems. In the end, I was imagining the on-board USB/LDO to only be needed if you were debugging or using it without Particle. For everything else, you could use the Particle power supply or power shields (which will work fine with the gateway) to get the desired result.

But if, as you suggest, the gateway shield should just always be used with a Particle device, then perhaps I should just remove the USB/LDO altogether. I just didn’t want people using their Core/Photons as very expensive power supplies :smile:


#7

@eric, I would keep the onboard USB/LDO. I have a situation where I could be using the gateway and a (12V) battery but it would be easy to provide an off-board step-down and simply provide the board with 5v via USB. Perhaps a couple of screw terminals into the LDO would be handy for that. That way power can be externally provided within the operating voltages of the LDO.