Ok, the project I'm currently working on requires that I communicate
with a PC using a PIC. I could go the standard Max232 chip to 9-Pin
Din route but one of my friends suggested using an FT232RL UART to USB
chip instead. The main advantage to this would be to power the entire
board off the USB power supply.However, as I understand it USB can
only take 100mA from the computer before having to actively request
more power which I don't have time to mess around with. So my question
is this, does anybody know approximately how much current I can expect
a PIC16F877A to use if I am using the UART and powering a couple of
other pins to output values to something else?

Thanks in advance for any help anyone can give

N...@googlemail.com wrote:
> Ok, the project I'm currently working on requires that I communicate
> with a PC using a PIC. I could go the standard Max232 chip to 9-Pin
> Din route but one of my friends suggested using an FT232RL UART to USB
> chip instead. The main advantage to this would be to power the entire
> board off the USB power supply.However, as I understand it USB can
> only take 100mA from the computer before having to actively request
> more power which I don't have time to mess around with. So my question
> is this, does anybody know approximately how much current I can expect
> a PIC16F877A to use if I am using the UART and powering a couple of
> other pins to output values to something else?
> 
> Thanks in advance for any help anyone can give

This board works fine from USB power and a PIC16F877a:
http://www.sparkfun.com/commerce/product_info.php?products_id=22#

Now, what else do you have connected to the 877 is another matter.

donald

N...@googlemail.com wrote:
> Ok, the project I'm currently working on requires that I communicate
> with a PC using a PIC. I could go the standard Max232 chip to 9-Pin
> Din route but one of my friends suggested using an FT232RL UART to USB
> chip instead. The main advantage to this would be to power the entire
> board off the USB power supply.However, as I understand it USB can
> only take 100mA from the computer before having to actively request
> more power which I don't have time to mess around with. So my question
> is this, does anybody know approximately how much current I can expect
> a PIC16F877A to use if I am using the UART and powering a couple of
> other pins to output values to something else?
> 
> Thanks in advance for any help anyone can give

Did you look at the data sheet for the processor?  Microchip usually 
goes into excruciatingly fine detail about power consumption.

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

On Feb 11, 8:55 am, NobodysHe...@googlemail.com wrote:
> Ok, the project I'm currently working on requires that I communicate
> with a PC using a PIC. I could go the standard Max232 chip to 9-Pin
> Din route but one of my friends suggested using an FT232RL UART to USB
> chip instead. The main advantage to this would be to power the entire
> board off the USB power supply.However, as I understand it USB can
> only take 100mA from the computer before having to actively request
> more power which I don't have time to mess around with. So my question
> is this, does anybody know approximately how much current I can expect
> a PIC16F877A to use if I am using the UART and powering a couple of
> other pins to output values to something else?
>
> Thanks in advance for any help anyone can give

General rule of thumb is 5 to 10 mA for the basic uC (PIC, AVR, etc)
and adding 5mA per LED.  100mA is plenty of current.

On 2008-02-11, N...@googlemail.com <N...@googlemail.com> wrote:
> Din route but one of my friends suggested using an FT232RL UART to USB
> chip instead. The main advantage to this would be to power the entire
> board off the USB power supply.

If your alternative is self-powered and rs232, you still have the option
of self-powered w/USB.

> only take 100mA from the computer before having to actively request
> more power

You can easily set this value on the FT232R using MPROG, which is the
FTDI setup utility.  Then you can have the 500mA max if you want.

-- 
Ben Jackson AD7GD
<b...@ben.com>
http://www.ben.com/