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Can I supply my BOE with 5volts to Vdd (X1,pin19) and if so do I need to tie Vin to ground? — Parallax Forums

Can I supply my BOE with 5volts to Vdd (X1,pin19) and if so do I need to tie Vin to ground?

connolly113connolly113 Posts: 8
in BASIC Stamp
Can I supply my BOE (usb style) with 5volts to Vdd (X1,pin19) and if so do I need to tie Vin to ground?

Comments

  • davejamesdavejames Posts: 4,045
    edited 2019-10-22 14:59
    connolly113 wrote: »
    Can I supply my BOE (usb style) with 5volts to Vdd (X1,pin19) and if so do I need to tie Vin to ground?
    ...hmmmmm, I would say "no" to both questions.

    If you haven't already, take a look at the BOE schematic. The output of VR1 becomes "VDD", ok - great. You could connect +5V to X1-19 and leave VR1-"VIN" unconnected. But the issue is (according to the schematic), VDD doesn't connect with the BS2; VIN does and uses the BS2 on-board regulator to produce +5V for the module's circuitry.

    So, unless the schematic is boogered, I'd say no.

    Now if you have an ohmmeter, pull the BS2 out of its socket and check to see if VDD on the schematic is connected to VDD on the socket pin 21. If it is, then "yes" to powering the BS2 as questioned (still leave VIN unconnected).

    Caution may be required should you wish to power other current-hungry circuits from VDD as noise, spikes, and voltage droop would cause havoc with the BS2.

    Hoping other, more seasoned Forumistas chime in,

    Dave
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    BS2-IC-Schematic-Rev-J_0.pdf
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    28850-BOE-USB-Schematic-D.pdf
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  • GenetixGenetix Posts: 1,742
    connolly113,

    What do you plan to use for 5V?

    Your 5V source MUST BE REGULATED and if you use Vdd for power then YOU CAN NOT USE Vin.

    It's safest to use a higher voltage, say 6V from batteries, through Vin since the BOE contains a 5V regulator.
  • connolly113connolly113 Posts: 8
    Thanks Dave for replying. You are right, I took out the stamp and the two Vdd's are not connected. It seems unusual to have two disconnected nodes on the same circuit with the same label.
  • connolly113connolly113 Posts: 8
    Genetix,
    I will use 6volts as you said, thks for the reply
  • Peter JakackiPeter Jakacki Posts: 10,193
    edited 2019-10-23 01:21
    If anybody said they were "supplying 5V" then I would assume in this day and age that this is +5V regulated from either a 5V charger or a USB battery pack. So yes, you can connect +5V to VDD, but no, never short the Vin of the regulator as that would force short-circuit current back through the regulator depending upon the type.

    Edit: you can short VDD to VIN though when supplying +5V directly.
  • davejamesdavejames Posts: 4,045
    connolly113 wrote: »
    Thanks Dave for replying. You are right, I took out the stamp and the two Vdd's are not connected. It seems unusual to have two disconnected nodes on the same circuit with the same label.

    Hey - you're welcome.

    Yeah, it's strange that the schematic would be so...but...there ya go. Always best to "ohm-out" when in doubt!

    :thumb:
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