Interfacing separate 3v circuit with 5v microcontroller

I'm working on a project that involves using a microcontroller's 5V output to make a connection between two points on a separate circuit (with it's own power source).

I'm using an Arduino, which is operating at 5V. I'm going to connect it to a wireless garage door opener and/or a remote (unlock/lock) for my car. The problem is that the circuits for both of these devices are operating at 3V, and the Arduino is at 5.

How would I take a 5v logic signal (0V for "off", 5V for "on") and use it to imitate button presses on these remotes? I've already "broken out" all the connections I want to make with wires connected to the remote circuits. What I'm trying to accomplish with the Arduino is the equivalent to touching the wires together to short them and complete the circuit.

What would be the best/easiest way to do this?

I'd really appreciate any help.

Trey

 

What you want is a buffer that has TTL thresholds and can work from Vcc in the range 1.65V to 5.5 Volts. It so happens there is a family of such chips from ON Semiconductor, Fairchild, and TI that does exactly what you want.

http://www.onsemi.com/pub_link/Collateral/MC74VHC1GT50-D.PDF
http://www.fairchildsemi.com/ds/NC/NC7WZ125.pdf
http://focus.ti.com/lit/ds/symlink/sn74lvc1g14.pdf

Only the one from ON Semi has true TTL thresholds. I thought the other two companies had similar products but I couldn't find them quickly.

 

or you can use simple transistors as a "buffer" ....



B. Morse

 

Thanks for the quick responses, those both sound like good ideas.

I think I'll try the transistors when I get home, since I already have some on hand. I tried briefly to set something similar up earlier, but I didn't fully understand how to set up the circuit. Your diagrams are helpful. I'll report back with results, and I'll be sure to post my project when it's finished.

Trey