What is the difference between V_out and 3.3?

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  • The Espruino Pico has two pins that seem to output voltage: V_out seems to output 4.8V, and 3.3 seems to output 3.3V (big surprise). What is the 4.8V for, and if I have a 5V or 3.3V tolerant device, can I power it off of either of these pins (connecting ground pin to - of course)?

    Also, it isn't entirely clear to me, and I don't think I can safely test this with a multimeter like the above, but what is V_IN for? Does it need to be a steady voltage or would a battery work?

  • EDITED after next post - #4 - from Narvey

    When USB connected, PICO's V_out is the power from the USB connection provided power of 5.xV going thru Diode D1 and is connected with the input for the onboard 3.3V regulator. If not connected, that is the pin that you can use to power PICO with 3.5..16V. See schema at https://github.com/espruino/EspruinoBoarĀ­d/raw/master/Pico/pdf/schematic_1v3.pdf as linked from https://www.espruino.com/Pico home page under Information section.

    The 3.3V output is the Espruino PICO onboard +power rail as regulated supplied by the onboard voltage regulator. It can drive up to 250mA... and gets warmer the higher the supply voltage is (as fed in on Vout). Therefore, if you have loads to drive, have an extra supply for the drivers that drive your loads and use Espruino only to supply control signals to the load drivers (BJT/MOSFET transistors,...).

    TL;DR[EDITED]: Connecting the Battery on J5 / BAT_IN will power V_out / V_BAT thru the onboard MOSFET Q1. MOSFET Q1 an Diode D1 build a protection circuit for the case that power is provided thru USB and connected Battery, and - with closed jumper - pin B0 can control powerflow to J5, the usual battery connection: batter can be charged, or - more exciting - if battery is put on BAT_out (see considerations below) , the MOSFET can drive loads that are connected to J5 (the usual BAT_in / battery connection.

    TL;DR[origin - still applicable]: The Diode D1 is there to prevent power going thru USB 'back' to your laptop (or whatever is USB connected) when you power PICO simultaneously thru Vout. There is though some caveat to that, because if your supplying voltage on V_ is lower than USB's 5V (more precise: lower than 4.8V), current will most likely / could flow and put load on the Diode D1 and USB power source with undesired (side) effects. Therefore, not to co-power is always safe. For simplicity and most of the time, I use the readily available USB battery banks to feed my PICO (and other USB) powered Espruino to run into issues (Note Espruino-Wifi does not have this protection like the PICO Diode D1 and must never be co-powered!)

  • I think @allObjects covered this nicely, but the naming on the pinout page at https://www.espruino.com/Pico#pinout makes this less confusing than the board's markings...

    • V_IN / BAT_IN is where you'd connect a battery - the Pico will use the battery power when USB is disconnected, and when USB is connected it'll use that.
    • V_out / VBAT is the output voltage. It's USB power (minus the diode voltage drop) when USB is connected, or when it's disconnected it is the battery power from V_IN / BAT_IN
  • It seems like @allObjects is saying connect the battery to V_out (a.k.a. VBAT), and @Gordon is saying connect it to V_in (a.k.a. BAT_IN) in order for the board to be able to handle any voltage between 3.7V and 16V. BAT_IN makes the most sense, so that is what I'm trying. I stacked up 2 CR2032 batteries to total 6.3V (approx.), and the red light constantly shines (which is what I got when I didn't have enough voltage, e.g. a single CR2032). What could that light mean this time?

  • and the red light constantly shines

    Were you holding down the Pico's button when applying power? It might just be in bootloader mode

  • @Narvey, you're absolutely correct... (and @Gordon was just a bit too nice not to point this out). Battery on BAT_IN in goes thru the MOSFET Q1 which allows a co-powering and even charges the battery (with closed P$1/P$2 solder bridge as described in schema) by pin B0. The other - very noteworthy - application of the MOSFET Q1 is driving a load connected to BAT_IN and Pico power is supplied thru USB or Bat_out.

  • solder bridge as described in schema

    Where? Can you point to this schema @allObjects?

    So to be absolutely clear I connect the battery (of any voltage between 3.7 and 16V) to GND and VBAT (right next to GND on the bottom of the pico diagram)? Someone should also update that page.

  • Sat 2021.01.30

    Hi @Narvey,

    re: 'Where? Can you point to this schema @allObjects?'

    I believe the reference is ao shorthand for 'schematic'. See first link in post #2. Seek the upper right hand side and view the horizontal double arrow gap next to label 'BO_Bat', and/or reference the notes below the table beneath heading 'Power, and the FET/B0 Jumper' on page:


    re: 'So to be absolutely clear I connect the battery'

    re: 'Someone should also update that page'

    Not needed. See your reference to @Gordons #3 post in your #4 post referencing the correct BAT_IN as you pointed out. @allObjects corrected the fubar in post #6

    See the same diagram in the link you posted in #7 beneath heading 'Pinout' and the note: 'VBAT is the battery voltage output'

    So, to power the Pico by battery would require using BAT_IN and GND

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What is the difference between V_out and 3.3?

Posted by Avatar for Narvey @Narvey