bells, buzzers, and whistles

[Al Skierkiewicz]

I suggested the LM386 since it is designed for low impedance loads. A speaker connected across one of the digital outputs will likely exceed the current rating on the driver trying to sink current with an 8 ohm load. A 1mmf/16v electrolytic cap in series with the input should handle most frequencies you send it. The chip is self biased for single polarity power and can operate down to 4 volts.
If you are using one of the piezo devices, a simple single transistor driver should work fine.

[Gdeaver]

Do you remember Monty Python's "The Meaning of Life" movie. The pregnant woman in the delivery room and the machine that goes "PING". You should have your own machine that goes "PING". I like machines that go "PING". They intimidate non-techies.

[Ether]

Originally Posted by Al Skierkiewicz

A speaker connected across one of the digital outputs will likely exceed the current rating on the driver trying to sink current with an 8 ohm load.

Yeah, it might not be able to source enough current to an 8 ohm load to be as loud as you might want.

It shouldn't hurt the transceiver though. RS-232 drivers and receivers must be able to withstand indefinite short circuit to ground or to any voltage level up to ±25 volts.

[Al Skierkiewicz]

The 9403 module is limited to 2 ma per output. Which transceiver are you referring to?

[Ether]

I was referring to the RTS pin on the cRIO's RS232 port.

On the PCs I have tested here, I can connect a small speaker directly to the RS232 port's RTS pin and -- by toggling the RTS line at an appropriate frequency -- get a sound loud enough to grab your attention from across a large room.