Hey guys,
Could you please help me to find the best way to get 5V to my circuit. I'm using the Seeed XIAO SAMD21 and that's what the input power has to be.
I would like to use my LiPo 3.7V battery to get 5V and consumn as less current as possible. The maximum current when it send data using LoRaWAN protocol through the LoRa-E5 is about a couple of hundreds of uA.
I was thinking of a small module, but I also saw I can use transistors. I'm a bit lost. I need your help.
Thanks a lot.
Laurent
Switch mode converters tend to use a lot of current, relativly speaking.
Two other options;
Use a low IQ 3.3V voltage regulator fed from the LiPo, and connect it direct to the 3.3V supply of the XIAO.
Connect the LiPo direct to the '5V' input.
Try both, take measurements and see what works.
You can get a XIAO SAMD21 down to circa 10uA sleep mode for a LoRaWAN node, so battery life can be into the years.
I don't think you can boost with just transistors. Anyway, I think a module is what you want. I usually use an MT3608-based module, but there are lots of different ones around. If you also need a charger, you might look at a J5019 module, which combines both functions. You would use a protected battery with most of these modules.
You don't have to power that board with 5volt.
That SAMD21 board seems to have a very low power LDO, with low dropout voltage.
I don't see why you can't power it directly with the 3.7volt battery on the 5volt pin.
When the battery drops to 3.5volt, the board should still receive a stable 3.3volt.
You can 'steal' maybe about 100mA from the 3.3volt pin to power the LoRa.
Leo..
I calculate about 60mA (22dbm).
Leo..
I believe you are on the correct track with a Boost Converter, granted it will take a bit of current so a careful choice needs to be made. A linear regulator will not work, the battery does this: " The lipo battery has a capacity of 70mAh at 3.7V, the voltage can range from 4.2V when fully charged to 3.0V when completely discharged . The battery includes protection circuitry to protect the battery from overcharging or completely discharging." **All linear regulators need an overhead so they can regulate. **They do not boost voltage. I have seen these available from China for maybe $3.00US or less, only problem is the delivery time. Good Luck.
The best solution is a SEPIC converter. The china boost converter I have can be set to 3.3V, with 4.2V in, they are not perfect. There is no need for a regulator.
?
I said that a boost converter wouldn't be needed.
Boosting a LiPo to 5volt and then dropping down to 3.3volt is only wasting power.
Leo..
That is not what I said, I added a line to clarify the answer.
What is the idle current of your proposed SEPIC converter.
Because that could be the deal breaker during sleep.
The linear regulator inside the Seeeduino has an idle current of 1uA.
Leo..
No, first try using the Li battery to power the SAMD21 directly as shown here. A boost converter followed by an LDO linear regulator is a considerable waste of power. So is a SEPIC converter.
The maximum current when it send data using LoRaWAN protocol through the LoRa-E5 is about a couple of hundreds of uA.
As stated above, the current is MUCH higher than that.
Works for me.
Switching converters become interresting with voltage differences of more than 1volt, and when no extreme sleep modes are used. Very good low-power buck converters (Pololu) can already do better with 0.5volt difference, but you could still be facing high idle currents during sleep.
Leo..
Thanks to all of you. Interesting conversation.
Unfortunatly, I can't check everything right as I'm at work and outside of my "lab".
But I understand I clearly underestimated this small XIAO and it seems I can directly power it on the 5V with my LiPo Battery.
Yesterday, I tried a few things and when I plugged the 5V with a USB cable, I checked the 3V3 output and it was not stable at all. I will try again with the LiPo and see how things going.
If I do that, can I recharge the battery if I plug the XIAO with the USB-C or I will have to unsolder it each time?
For the ESP32, I need to do a deep sleep. But it seems it is not necessary for the XIAO, right?
Your question in the first post was about the SAMD21, and you said;
"and consumn as less current as possible"
So yes it is necessary to use sleep mode on the XIAO SAMD21.
Remember that LoRaWAN nodes are mostly powerd off, only waking up to send data every 5 minutes or so.
Yes, but not at all safely. You need a charge controller.
If you want a self contained, well designed, reliable system with a battery that can be automatically recharged in that way, I strongly recommend the Adafruit Feather rechargeable series with LoRa.
Yes I guess. Thanks
ok, got it. I tried to find info on this XIAO module. Not too much info. I'm trying to find a way to put it into sleep mode (standby mode actually if I'm not wrong). I found the RTCZero library but still have problem using it. I'm not giving up but just in case, is there another one?
The RTCZero library works very well indeed for the Seeed XIAO SAMD21, why would you need another one ?
That's what I thought. I used the "SleepRTCAlarm" example but I just need to play around so it wakes up every 2h, and not at a certain time.
Thanks again @srnet
Its not difficult to add two hours to the current time and set the alarm for that.
However the ArduinoLowPower library supports the SAMD21 and uses its RTC to allow this type of deep sleep;
LowPower.sleep(seconds * 1000);
I found this LowPower library a few minutes ago but didn't have a chance to test it. Thanks for letting me know.
Actually, I just found this alternative with the RTCZero library using:
rtc.setAlarmSeconds(20);
rtc.enableAlarm(rtc.MATCH_SS);
It will run the loop each time it matches the seconds.
Now, I'm facing another problem. Ihave actually 9mA during the standby mode! I have my 2 sensors controlled by a 2N3906 transistor (controlled by the XIAO on pin 8), and the LoRa-E5 powered with the 3V3 output of the XIAO. I'm measuring the current through my battery which is then plugged to the VIN of the XIAO.
Maybe the LowPower library will help?!