Shop OBEX P1 Docs P2 Docs Learn Events
Getting the power out of USB — Parallax Forums

Getting the power out of USB

inakiinaki Posts: 262
edited 2005-06-09 17:12 in General Discussion
I am working on a project that will connect to a PC using a FTDI USB/Serial port.
The board uses 5V to work so I was thinking on using the power that comes out the USB port.

Is there any ready made FTDI board that provides +5V on the output connector ?

I got·a FTDI mini-board·but the +5V pin is not connected. Of course it·would be·possible to·reach the power pin using an extra·wire.

By the way, is·there an FTDI chip in DIP package· ?··

Comments

  • ForrestForrest Posts: 1,341
    edited 2005-06-08 13:16
    DLPDesign has some FTDI USB to RS232 boards in a DIP footprint www.dlpdesign.com/usb/
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-06-08 14:13
    Hello,

    ·· Also bear in mind that there is a limit to how much power you can safely draw from the USB port.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • Paul BakerPaul Baker Posts: 6,351
    edited 2005-06-08 14:38
    Chris is correct on that point, the FTDI chips support 100ma of current drawn from the line. Not only that but USB specifications state that a USB device may not draw that current until negotiation has completed (it think your can draw ~10ma before negotiation completes). I believe that the FTDI chips will hold the RSTOUT line low until negotiation is complete so a microcontroller operating off of USB power should have RSTOUT tied to the reset pin to prevent the microcontroller from drawing current until it is permissible to do so.
  • inakiinaki Posts: 262
    edited 2005-06-08 18:35
    :-(

    I was thinking to·use about 160mA. I thought I had available all USB·current (500mA)·but did not count on the FTDI itself! It is too bad. My·project looses a lot of interest if I have to·provide it with·a separate power supply.
  • PLJackPLJack Posts: 398
    edited 2005-06-09 16:11
    Anyone know how the USB work/night LED lights work?

    I can't believe that they have an IC negotiating with the USB bus.
    Not for $4.99 retail.
    Bright white LEDs take more that 10ma.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Jack
  • SteveWSteveW Posts: 246
    edited 2005-06-09 17:12
    Those USB lights just take the power regardless. They're not USB compliant, but they work in most ports. (The port isn't obliged to deliver the power, but very few have any power management more cunning than a fuse, or a maximum current limit - I don't think I've ever seen an implementation that applies the pre-configuration limit strictly - maybe we'll see more of that when USB-otg starts to deliver host ports on power-limited battery operated gear. )

    Steve
Sign In or Register to comment.