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Topic: Getting +5V output from Sparkfuns FTDI BOB (Read 859 times) previous topic - next topic

Makkan

I know this is the wrong forum for this question. But since it's quite related and you guys are awesome I hope you folks won't mind.

The question in question:
I recently bought this FTDI breakout board from sparkfun.
http://www.sparkfun.com/commerce/product_info.php?products_id=718
And according to their site you are supposed to get 3.3 V output from the 3V3 pinout. Well that's no problem I do get that. But I want to use 5V. For this there is some sort of solder jumper that I'm supposed to do something with. The problem is I don't have a clue what to do. I can't find any information on their site, atleast that I understand. In their comment section on the product page someone else asked how exactly one was supposed to handle this solder jumper but so far there hasn't been any replies.

Also there is a pin called VCC that I measure +5V. But from the FTDI spec sheet this pin is not an output pin so I dare not use it.

To make this question even more legit I can tell you that my project involves an arduino, a radio transmitter, a radio receiver and a the afformentioned break out board.  8-)


retrolefty

#1
Jun 12, 2009, 09:39 am Last Edit: Jun 12, 2009, 09:41 am by retrolefty Reason: 1
Yes, I also have that Spark fun module and have done the 5volt I/O mod. First what the mod does. As delivered the digital output pins of the FTDI chip goes from 0vdc for a low to 3.3vdc for a high. If you need or want full 5vdc logic voltage ouput from those logic pins then you need to do the mod.

The mod:

As shipped there is a connection path between pins 4 (VCCIO) and pin 17 (3.3v) on the FTDI chip (not the pin numbers of the module). If you cut the trace connection between 17 and 4 (called SJ2 on the drawing) and then solder a wire from pin 4 and any convient point that has +5vdc you have completed the mod. The FTDI chip will then do a full +5vdc logic swing on it's output pins rather then a +3.3vdc swing.

I did it by cutting the connecting trace pad, SJ2 and wiring a jumper from pins JP1 pin 4 (VCC) and JP2 pin 4 (vccio).

There is a link on Spark fun product page showing the schematic drawing of the module:

http://www.sparkfun.com/datasheets/BreakoutBoards/FT232RL-Breakout-Schematic.pdf

PS: Good module, gives you all the options that the FTDI can do and I like the mini USB connector small size.

Lefty


Makkan

Ok, I was hoping to get just +5V to use as a supply to the radio receiver. Is that possible witout doing that whole mod thing? Although it should be fairly easy to do what you just described. Infact on a breadboard it would be really easy (except for the fact that they put the text on the underside, hmm I should make some sort of break out label).

And what is that pin? VCC, from what I can understand "common collector" would be the input pin if I were to draw power from an external source other than the USB-connection.

I picked it up because Tom Igoe uses it (the previous version) extensively in the book "Making things talk" And I've already had some fun talking wirelessly with my arduino. That is until I "let the magic smoke out" of my radio receiver.

retrolefty

#3
Jun 12, 2009, 11:17 am Last Edit: Jun 12, 2009, 11:20 am by retrolefty Reason: 1
The VCC pin (JP1-4) is just the symbol for +5vdc power voltage that comes from the USB connector. You are limited to how much current you can draw from this pin, the schematic shows a 500ma fuse. You are free to use this voltage to power anything you want externally to the module as long as it doesn't exceed the current limit. The mod I described is only required if you need 5vdc logic level outputs and is not required if what you are wiring to can except 3.3v logic signals. There is also +3.3vdc power voltage avalible at the module, JP1-5, That you can use to power things externally to the module, but I think it has a very low current capacity of say 50ma or so.

Lefty


Makkan

Ah ok!
Thats even better than I hoped. That radio receiver I have shouldn't draw anywhere near 500 mA.

But just to be sure: Should I read the schematic as follows. VBUS voltage output goes through the 500 mA Fuse (F1) and to chip VCC (pin 20 on the chip). This pin is broken out to VCC (JP1-4) on the break out board. Which means it doesen't go through the chip it's just connected to it. I.e anything drawin power from this pin will draw power from USB and not from the chip.

retrolefty


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