Powering a 5v device via Electron's LiPo

Powering a 5v device via Electron’s Lipo

Hello, I’m using an Electron to read values from a temperature sensor which requires 3V and an air quality sensor with requires 5V. I’m powering the system with a 3.7 Lipo battery and I’m using a Boost Converter from Adafruit to step up the voltage to 5v to power an air quality sensor which draws about 250mA.

I see three different options to connect the voltage booster, and I wonder which is the best or if there’s any difference at all.

See my drawing.

#1: Boost converter attached to the 3.3v output on the electron in parallel with the 3V temp. sensor
#2: Boost converter attached to the LiPo in parallel with electron
#3: Boost and LiPo attached to the Vin of the electron.


I’d suggest #1.
#3 is out of question since Vin is not powered when there is no VUSB present.
#2 may be problematic when the LiPo is below a save SoC to power the Electron but the directly connected devices still drawing current further depleting the battery.

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Thanks @ScruffR!
My only concerns with #1 is the high power draw on the Electron 3.3v, plus I feel I’m loosing efficiency with respect to #2 since the ~3.7V of the Lipo are first regulated down to 3.3V and then boosted up to 5V. Going with #2 would save one step (~3.7v -> 5v)

If you can accept the potential risk of depleting the LiPo beyond a level where the Electron can safely operate, you can go with #2 (at your own risk).

The 3v3 pin can source up to 800mA ontop of the regular demand of the device itself.

This topic is a bit old but I’m looking for a similar project and trying to figure out the part list needed. The question is about the consumption on the 3v3 out pin when the board is in deep sleep with option#1. I can’t trust myself to figure out the datasheet. Wondering if I should add a mosfet to avoid leakage to this pin when sleeping. I’m looking for 0 battery drain from this pin when not needed and the sensor (https://media.digikey.com/pdf/Data%20Sheets/DFRobot%20PDFs/SEN0208_Web.pdf) use 5ma on idle.
-For Remote Battery operated monitoring project.


@Squid, if you have Version 2 of the JSN-SR04, you can use Mode 3 seen Here .

Mode 3: R27 = 120K. In the serial port mode
After the module is powered on, the module enters standby mode. 
When the RX port receives the 0X55 instruction, the module starts a ranging and outputs one frame from the pin TX with four 8-bit data. 

I’ve used that Sensor with the 3V3 pin on a Battery Powered Photon with no troubles.
I’ve never measured the standby current, but it’s probably higher than using the mosfet as you mentioned.
I suppose you could power the sensor via an Output Pin as well.

I assume this is also true for all the Mesh devices?

Yes, it is.

Thanks for your reply. So this sensor is splash proof and really working on 3v3? About all datasheet from the rev2 state 5V supply, it’s strange how chineese stuff is not accurate. Also there is no IPX information for dust and water protection.

From what I’ve seen, the use of this sensor is a bit hard to figure out, some ppl use longer pulse to make it works.

returning to my question, I would like to know if the sensor will drain current from the 3v3 pin when in deep sleep or it’s good to go and no mosfet need to be added. Remember I need about no leakage from this pin. My mosfet research are a year ago, do you have in mind a N channel fet full open with 3v? Also a simple diagram on how to wire this thing.

I use the JSN-SR04T in my project. It can be powered both 3V3 or 5V. Personally, I didn’t notice any difference between this, but there’s some anecdotal evidence suggesting some found it to be more reliable when powered by 5V? Anyway, I 5V-power it in my project.

The sensor has a quiescent current of approx. 10-15mA. You will need to cut power to it somehow if you want to prevent it from draining your power source.

In my experience, the transducer is decently water and dust proof. I had mine under a running water tap for 10-20s and inside waste containers for months (dust) and they still all worked fine.