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Topic: Isolating VCC in circuit (Read 2 times) previous topic - next topic

retrolefty

#25
Feb 23, 2012, 09:01 am Last Edit: Feb 23, 2012, 09:03 am by retrolefty Reason: 1

By the way, should those series resistors on the TX/RX lines be 1K, or 10K?  Somewhere someone told me to use 10K, but I can't remember anymore where ...  Does it make a lot of difference, such as completely rendering those lines "dead", preventing a reprogram?


The arduino design uses 1k isolation resistors, but I suspect 10k would might work also, but best to stick what has been proven to work over all the baudrates used on FTDI based arduino boards.

http://arduino.cc/en/uploads/Main/arduino-duemilanove-schematic.pdf

Lefty

MarkT

Dont forget decoupling caps BTW
[ I won't respond to messages, use the forum please ]

KirAsh4


Dont forget decoupling caps BTW


Yup.  I didn't put them in the posted schematic because it was 'in it's simplest of simple form', where all I cared about was the VCC lines.  The actual schematic has a lot more stuff in it, decoupling caps from here to the moon and back is just one of those things.  *grin*

Brad Burleson


Basically, if ONLY the external PSU is connected, I don't want (or need) the FTDI IC powered up.


So I'm probably missing something, but I have to ask:

If you don't always want to use the FTDI chip, why don't you simply put an FTDI 6pin header on the board and then use an FTDI cable (or a USB/TTL Serial adapter) when you need it?

I'm probably missing something...

Brad.

PS I like Lefty's idea of using 3 0.1" headers as your on-board switch.  Then if you want a real switch, simply wire one up with a small jumper (w/ female pins).  Of course this takes a bit more enclosure space but it's more flexible.

retrolefty

Quote
I'm probably missing something...


Yes. He wants the board mounted FTDI chip to draw power only if it's actively plugged into the PCs USB buss. It's a current saving thing that some want or need and as the Seeeduino design allows. Using an external USB serial cable or module is another way of accomplishing the same thing.


Lefty

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