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Re: Serial port power draw.

From: Doug Sutherland <>
Date: Sat, 3 Mar 2001 17:34:20 -0800

James,

I still think that DS275 is a better alternative. It has two 5 volt input 
pins and uses an internal voltage doubler and inverter to generate the +/- 
10 volts for RS232 compatibility (instead of external capacitors). 

> Does that mean I will need to power the MAX232 off of something 
> other than the serial port?

I'm a bit confused by this. Are you planning to power the PIC off some 
other serial port? If not I say skip all that nonsense and just use 5 
volts from a regulator, for both the PIC and MAX232. The number of 
circuit diagrams in the MAX232 data sheets ismind boggling. For  simple 
RS232 conversion to connect the PIC to a PC, all you need to connect 
on the MAX232 is 5 volts and GND, TTL in and out, and RS232 in and out. 
You usually also need to add a bunch of capacitors to generate the 10 
volts, although there are some versions of MAX232 that don't require 
this. The DS275 is much simpler. It's designed to do exactly what you 
are doing in a simple and small form factor. The venerable MAX232 is a 
lot more flexible, but flexibility always costs in one way or another. 
I bet the DS275 draws less power too. Check out the data sheet ...

  -- Doug

  Does a max232 draw more power,
> where it would exceed the spec of no more than 5mA?  A 16c71 draws about
> 2mA;  I can't expect that the MAX232 would draw more than 3, am I wrong?
> Am I missing some other crucial point here?
> 
> 
> 
> James Davidheiser
> Drexel University
> Department of Physics
> 
> "Tell a man that there are 400 billion stars and he'll believe you"
> "Say a bench has wet paint and he has to touch it"
> 
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