Cut off power to connected hardware (Electron)

Hello Particle Community!

I’ve got a particle electron in deep sleep mode with a 4-20mA current loop receiver attached via I2C. The problem is that the attached hardware is still powered:

Is there someway to cut the power in software or do i have to use some sort of hardware setup for this?
How would i do this?

Thanks in advance,
Michael

In deep sleep all GPIOs (but WKP) will go to High-Z state and Vin/3v3/Li+ will still be powered as if the device was not in deep sleep.
So in order to cut power to external circuitry you need to power this via some kind of switch (e.g. FET) that - by default - cuts the connection between your Vin/3v3/Li+ supply and only reapplies power when a respective GPIO pin is activated.

Since you are using the Electron in a 3rd party board, you may need to contact the creator of that board whether or not there is any means to do that already. If not, you may be stuck with at least some permanent current draw caused by the “main board”.

But visiting the creators forum you may find these threads
https://forum.ncd.io/content/Turn-power-draw-Particle-Electron-IC2-battery-only-shield
https://forum.ncd.io/content/Power-Connection-PR35-17-board

Well apparently it didn’t work out after all, and they withdrew the board from purchase :frowning:

I’ve been looking at MOSFETs for the job like you said, but i don’t have the slightest idea what kind could be used for this purpose? do you have any guidelines to what kind of specs i should be looking for? - or even a link to something?

Thanks in advance,
Michael

From a HW perspective, a load switch would be a good way to remove power from the sub-system. Here is a link to an application note on load switches for reference.

2 Likes

Nice document @dmfische ! - especially for a FET rookie like myself.

I found these:
https://www.diodes.com/assets/Datasheets/AP2280.pdf (P-channel)
https://www.diodes.com/assets/Datasheets/AP2281.pdf (P-channel)
https://www.diodes.com/assets/Datasheets/AP22800.pdf (N-channel)

Could these potentially work?

thanks

Michael

Thanks. From a quick glance of the three datasheets, I think that these could all work. As a disclaimer of not knowing the full/precise setup, think I would personally go with either of the P-channel load switches for a variety of reasons (lower Iq, simpler design).

However I suggest that you look into load switch IC development kits as a first step. This could be easily integrated into your setup and you could test the design (HW+FW) prior to going to a custom PCB.

I don’t seem to be able to find anything when searching for load switch IC development kits on google.
It would be nice with a breadboard friendly load switch so that I could test as you said, but I can’t find anything.

Either I’m searching wrong or I’m missing something?

An example or link would be very much appreciated if possible :wink:

I’m gonna read up on MOSFETs until tomorrow, as I don’t really understand how they work.
Maybe i have better luck searching for what i need, when I actually understand what FETs do and how they work.

Thanks

Not a problem. :slight_smile: Here is one dev kit I found on google:

https://www.mouser.com/ProductDetail/ON-Semiconductor/NCP334FCT2GEVB/?qs=664zcAxDQ0kGEu4zcteYxQ%3D%3D&gclid=EAIaIQobChMI6e-1-5f72QIVRLXACh0VRAXAEAQYBCABEgKe-PD_BwE

I found a through hole option for you, so should be easy to wire up.

https://www.mouser.com/ProductDetail/Texas-Instruments/TPS2034P?qs=sGAEpiMZZMuCmTIBzycWfArOWgm%2bsETdZ0e9s6J5THw%3D

There is an example circuit in the data sheet. The EN pin will go to a GPIO pin of your choice, and just add a resistor to from EN to GND. Something in the neighborhood of 4.7 - 10k should be good.

A N-Channel fet can do the same thing, but as you said if your not that familiar with them, this would be another way to go.

Here is a little tutorial on transistors & fets to get you started.

I’ve used these successfully.

That is a cool product, cant believe it’s that cheap. It does not say what the drive current is for the LED and OPTO though. I am curious how much that is as it does not state what opto they are using.

Thank you for all your links!
VERY much appreciated :wink:

I will have a closer look at them and figure out what to buy.
when I get it to work I’ll post an update on what I did.

EDIT:
I’ve bought the Gravity MOSFET Power Controller (DFR0457) and the Power Switch IC (TPS2034P) that @seulater and @RWB mentioned.
(btw a nice explanation video @seulater! I learned a lot)

I want the Power Management IC Development Tool (NCP334FCT2GEVB) that @dmfische mentioned to test out as well, but the price is a wee too spicy for me atm for these tests :frowning:

I also bought “Switching Voltage Regulators 3.3/5/AdjV-Out Step Up DC/DC Converter” to step up the 3v3 to 5v.
link: https://www.mouser.dk/ProductDetail/Maxim-Integrated/MAX756CPA%2B?qs=sGAEpiMZZMtitjHzVIkrqc6gsJXSSM1sceqmv5cxfao%3D

I’m gonna post a result when I get the items and set it up.

1 Like