Help Several rfm « Jee Labs Talk

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Help Several rfm

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tyran

Hello can I use several rfm12 at the same time? (yes I know only b provides grouping)
The idea is a robot passing through and connecting to several receivers then listening theirs response (one at a time of course)...

The problem with the rfm12b is the logic level because of the robot and sensors that receive for example output from an opamp so I wanted to keep the 5V there.

But If I choose the rfm12b can the outputs of the transceivers connect directly to my uC? And on the other way around (controller->transceiver) I would use a resistor voltage divider.

Appreciate any help :)
Thanks :P

Posted 04/01/2010 08:32:09
kellerza

If you want to connect serial busses (SPI for rf12) I'd suggest bidirectional level shifters

A bi-directional level shifter can easily be done with a FET (I use a BS170, TO-92 package), which mounts easily on a port expander board.

FET bi-directional level shifter:
Connect the Gate-PIN to the lower voltage supply/v+/3.3V
Connect the Source-PIN to the lower voltage data pin
Connect the Drain-PIN to the higher voltage data pin
Both circuits must share ground and you need pull-ups on both sides

To send data, you have to change mode to output and set value to 1/0

To receive data with pullups, set the mode to input and set the pin to 1 (activates pullup)

These FETs are cheap and quite versatile, connecting it up differently you can easily switch higher voltage/current outputs. Gate on uC, Source on GND, Drain on Load, load connected to higher voltage (5V/12V etc)

Posted 04/01/2010 10:38:15
jcw

Fascinating stuff - I also found this article: http://www.rocketnumbernine.com/2009/04/10/5v-33v-bidirectional-level-converter/

Posted 04/01/2010 17:06:08
kellerza

Neat, http://www.rocketnumbernine.com/2009/06/13/bidirectional-level-converter-pcb/ could almost be a 3.3V to 5V level shifting "AnyVoltage" JeePlug :)

Posted 04/01/2010 20:42:48