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Powering BS1 USB without USB Connection? — Parallax Forums

Powering BS1 USB without USB Connection?

Bill ChennaultBill Chennault Posts: 1,198
edited 2011-01-21 14:43 in BASIC Stamp
All--

Is it possible to power the BS1 USB without a USB connection? +5vdc on VDD and -5VDC on VSS?

Thanks!

--Bill

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2011-01-20 20:49
    Yes, but you probably mean +5V and 0V attached to Vdd and Vss respectively.

    You might have problems with the +5V feeding back into the FT232R USB to Serial adapter chip. I know on the Prop that can cause problems with Reset, but, on the BS2, the Reset line is usually capacitively coupled which avoids the problem. I haven't seen a schematic for the BS1USB, so I can't tell for sure.
  • Bill ChennaultBill Chennault Posts: 1,198
    edited 2011-01-20 21:06
    Mike--
    You might have problems with the +5V feeding back into the FT232R USB to Serial adapter chip.
    Forgive my ignorance, please. Are these issues avoided by not having a USB connection at the same time power is supplied via Vdd and Vss?

    EDIT: Changed Vcc to Vdd.

    --Bill
  • Mike GreenMike Green Posts: 23,101
    edited 2011-01-20 22:47
    Normally the FT232 chip gets its power from the USB cable and passes it on to the Stamp. When there's no USB cable, there's no power, so the chip is off. If you provide +5V to the BS1USB, it goes back into the FT232 chip through the output pin and "sneaks" through pathways in the chip to provide power to it. Sometimes this "sneak" power path doesn't work normally and the DTR line, which is used for the BS1's reset, doesn't work right. This is true for the Propeller. I'm not sure if it works the same way with the BS1USB.
  • bsnutbsnut Posts: 521
    edited 2011-01-21 00:41
    Could a diode shove this problem with the 5+ feeding back?
  • Mike GreenMike Green Posts: 23,101
    edited 2011-01-21 09:11
    A diode could, but there are two problems:

    1) Where would you put it and how would you connect it? The BS1USB board is very crowded and very small

    2) A diode has a drop across it of around 0.6V. In a 5V circuit, that would drop the voltage to 4.3V. USB doesn't always supply 5V, so the voltage available to the BS1 might often be less than 4.3 which would cause the BS1 to reset.
  • bsnutbsnut Posts: 521
    edited 2011-01-21 14:28
    I see your point Mike and the last post was done on my phone at work
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-01-21 14:43
    Take a look at these products:

    -Phil
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