2 Application questions about mesh products

[TomEldredge]

1. Can a xenon run application code without being connected to the cloud and without trying to connect to the cloud? I need to use the SPI, CPU and the I2c and later connect to the cloud when the mesh products become stable and when Blue tooth range is adequate, but I would like to begin hardware design using the mesh devices for the future.

2. Mesh device charging circuit. The mesh products can run with the Li battery, but the Li will have to be charged when not connected to the PC. Do you apply the external charging voltage to the USB pin? Do PC’s usually have diode protection on the USB to prevent conflicts with other external charging voltages? Presently we use the Electron and I think we charge through the VM pin. No such pin on mesh devices.

[ScruffR]

@TomEldredge

Can a xenon run application code without being connected to the cloud and without trying to connect to the cloud?

Yes, when using a non-AUTOMATIC SYSTEM_MODE

@TomEldredge

Mesh device charging circuit. The mesh products can run with the Li battery, but the Li will have to be charged when not connected to the PC. Do you apply the external charging voltage to the USB pin? Do PC’s usually have diode protection on the USB to prevent conflicts with other external charging voltages?

You can connect a USB charger or supply 5V to the VUSB pin.
The docs do feature a block diagram that shows the input power block
https://docs.particle.io/datasheets/mesh/xenon-datasheet/#block-diagram

@TomEldredge

Presently we use the Electron and I think we charge through the VM pin

What is the VM pin? Do you mean Vin?
On mesh devices VUSB is the same thing as on Gen1&2 devices Vin but there is no protection diode between USB and Vin to prevent back-feeding into the USB port.

There are some posts that address the potential back-feeding and possible workarounds (if needed)

Power to boron / xenon

Unlike the Electron/Photon on mesh devices there is no protection diode between the USB connector and VUSB. So when supplying power both ways you need to be extra careful (others even suggest to keep it mutually exclusive) but grounding EN does not mitigate the potential danger for your USB port in case of back-feeding via VUSB in any way. What you can do is to manufacture a custom USB cable which disconnects the USB Vcc line. I’ve 3D printed myself a little insulator inlay for the USB-A conn…

[Mapoint]

Hi ScruffR
I purchase 3.7V lipo battery with 2 pin JST connector and it fits It is 600mAh far less than 1800mAh that is sold by Particle.io store I looked up the datasheet on xenon and it says the USB port must provide 500mAh however Nothing in connection to wattage requirements for Xenon to power on using the Lipo Battery. I wonder where is the sweet spot for Xenon to power on Somewhere between 3.7V x 1.8AH = 6.66W and 3.7V x 0.5Ah = 1.85W

[ScruffR]

Ah (Amper x Hour) is not the same as A (Ampere).

@Mapoint

3.7V x 0.5Ah = 1.85W

Actually no, it would be 1.85Wh - you can't just drop a unit.

A 600mAh battery can typically still drive the same amount of current, just not as long as a 1800mAh batter.
When you have a 1A load on your battery the smaller one will drive that for 36 minutes while the larger one will last you 108 minutes.

@Mapoint

datasheet on xenon and it says the USB port must provide 500mAh however Nothing in connection to wattage requirements for Xenon to power

Actually it does - just not as wattage but as current draw.

Multiply that with the 3.3V the system runs on to get the wattage.
When we allow for some safety margin with 10mA that would give you

3.3V * 0.010A = 0.033 VA = 0.033W

Or in or in terms of battery life time (for the sake of safety margin and ease of estamation take 3.7V instead of 3.3V)

600mAh / 10mA = 60h

(see how the units don't just disappear)