Triggering power on a 5V unit from a 3V unit

Hello again,
I have a microcontroller that works at 3V controlling a RFID reader that works at 5V. I would like to enable one of the pins of the microcontroller to trigger the RFID reader to start. I was thinking of using a relay, but knowing that the microprocessor only outputs around 5mA, 3V once that pin is set HIGH, it might not work. Any ideas?

EDIT: Looking at the datasheet, I might be able to get out around 5-15mA of current through those 3V ports.

In case you're wondering what devices I'm talking about:

IRIS Mote (datasheet) (scroll to page 23/53 to table 6-3 for current specifications):
https://www.google.ca/url?sa=t&rct=j&q=mpr-mib_series_users_manual&source=web&cd=2&ved=0CC4QFjAB&url=http%3A%2F%2Fwww-db.ics.uci.edu%2Fpages%2Fresearch%2Fquasar%2FMPR-MIB%2520Series%2520User%2520Manual%25207430-0021-06_A.pdf&ei=VOdwT7aAIIHG2wWiuMjyAQ&usg=AFQjCNEpjoRF5dupr_NkfYFTJxLEfDOBeA&cad=rja

RFID Reader (datasheet):
**broken link removed**

Also, I could try and trigger one of these ports to work through an current meter so i could really measure how much current passes through these ports. For now, all I know for sure is that they can be set to 3V.

How about an Opamp?

You're right! One way I could do it is with a Schmitt trigger!
Thanks!

I've decided to use MOSFET relays to do this job. They seemengly have very low voltage triggering (~1.15V) and low input current (~10mA). Does anyone have an idea of any good, popular MOSFET relays that will trigger from ~2.5V down and with at most 10-15mA of current?

Thank you!

EDIT: The relays I found were from OMRON: G3VM-21LR1.

Why don't you use n-ch MOSFET open drain switch, where MOSFET drain is connected to 5Volts through a resistance of your requirement? 3V uP pin is loaded to gate of MOSFET and Drain may be used to switch the RFID.