Is 5V necessary?


  • Pybytes Beta

    I was running my WiPy on only the 3.3V input and occasionally getting core dumps. Added power on the 5V input as well and seems to be stable. Is this strictly necessary or do I maybe just have too many peripherals and if so, how could I determine that?


  • Pybytes Beta

    You rock.



  • @BetterAuto I just gave it a try:
    Pololu 7v8FA (which is the adjustable model):
    Vin 4.5 V, Vout set to 3.3 V

    • Quiescent Current w/o load: 50 µA
    • Input Current with a 100µA load: 130 µA
    • Input Current with a 1 mA load: 860 µA

    The input current is lower than the output current, because Vin is higher than Vout and it's a switching regulator.


  • Pybytes Beta

    Ahh, pass-through. Wasn't aware of that.

    I had oopsed and read your comment as 1mA but 0.1mA is within my power budget. Obviously lower is better though.



  • @BetterAuto the Lm3281 is step down only. If the input is too low, it will go into a pass-through mode.
    At .1 mA for the regulator, it will use about 880 mAh alone for standby per year, plus the power needed for the circuitry. A D cell is rated at 5000 mAh, maybe more.


  • Pybytes Beta

    Six months to a year. How is it the LM3281 can output 3.3V with an input of 3V? I thought input voltage had to be higher than output for regulators.



  • @BetterAuto I personally used a module from Pololu, model S7V8F3, which is a step down/step up regulator, which will output 3.3 with an input voltage between 2.7 and 11.8V. https://www.pololu.com/product/2122
    The module (or chip) suits perfectly for your needs of a supply by battery.
    The quiescent current of the module is specified a below 0.1 mA, but that varies with the input voltage & usage. The LM3281 used by Pycom ist specified with a quiescent current of 16 - 30 µA.
    By the way: what do you call "a long time on batteries"?


  • Pybytes Beta

    @robert-hh Humm, hadn't thought of that. And two alkaline cells at a starting voltage of 1.65V could only power it for moments before dropping below 3.3V.

    I want to run a long time on batteries, sleeping most of the time. Is there a recommended regulator (switching or linear) with a low quiescent and high efficiency?

    I can go look at DigiKey, just wondering if there's one people often use and recommend.



  • @BetterAuto WM01 you still need a regulator. 3 D Cells will have a voltage of 4.8V down to ~3 V.


  • Pybytes Beta

    Thanks much. Will use three D cells. And copious deep sleep time :-)



  • @BetterAuto Yes, you cannot supply the WM01 differently. And with WIPy,. LoPy and SiPy, Vin is sufficient, because they have an on-board regulator, which can also be used to drive additional peripherals.


  • Pybytes Beta

    So it sounds like you're saying with this setup 3.3V should be sufficient.



  • @BetterAuto According to the specs, there is not regulator in the WM01. So you have to build the supply circuitry your own and provide 3.3V to the WM01.


  • Pybytes Beta

    Thanks for the info everyone. It probably is my supply, will try a different one. Already using a biggish cap.

    So robert-hh is saying it's better to use Vin. Is that also a recommendation for the W01? I'm building a battery-powered product and want to integrate that chip. I had wanted to use three D cells and avoid using a boost converter.

    In your opinion should I use Vin for this?

    If I switch any of my peripherals to lower powered varieties could 3.3V be made to work?

    Or would you switch to four cells/use a boost?

    Peripherals:

    • External antenna
    • DS3231 RTC, 4.7k pull ups
    • ULN2003 for driving three LEDs and a solenoid
    • ESP8266 for driving a camera, connected via I2C and serial
    • Two L9110S driving two motors
    • Several switches
    • Four voltage dividers to read voltages from the motors, on input pins
    • Future expansion possible with connections to I2C and serial


  • @BetterAuto From the experience of others it's better to supply at the Vin pin. The input voltage may go down to 3.6V, before the internal regulator switches to pass-though. You may still use the 3.3V Pin to supply other devices. It is specified for up to 1.2A.



  • yes,quite necessary..***

    • [bolded text](![link url](image url))***


  • @BetterAuto Perhaps you have a bad/poor 3.3v power supply. I've been doing exactly what you describe with a high-quality digital bench supply, and I've had no problems. Another possibility is that your power supply isn't capable of delivering peak current to the WiPy--WiFi needs peaks of 250mA while transmitting--and if this is the case, you might be able to solve it by adding a significant amount of capacitance (even a small SuperCap).


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