Serial between two Arduinos?

I want to get one Arduino to talk another Arduino that's about 50 feet away. Can I use serial for this? I know RS232 has a distance of like 100 meters, but this isn't RS232.

How would I wire it up? Just TX on one, to RX on the other?

More specifically I’d like to have a remote Digispark phone home to my main Arduino that’s about 50 feet away. I play on running four wires between them: 5v, ground, TX, and RX. Is that workable?

Sure. Get some CAT5/ethernet cable and connect them up. Start with slower speeds, work up until comm's get unreliable, and then back down.

I have similar small boards available as well, with '328 family or '1284 chip family. User assembly required at the moment. Am working on a reflow oven controller to put chips on myself.

Do I need pull up resistors or anything special? Just RX->TX and TX->RX?

Just Rx to Tx, Tx to Rx, Gnd to Gnd.

For long transmission lines, you should use a slower baud-rate to decrease the transmission-error probability. Or you can get a MAX232 chip for each arduino, and transmit at the at RS-232 voltage levels, to increase signal integrity.

What's considered a "long transition line?" I'm probably going about 50 feet... maybe 75. I planned on use 28800.

28,800, you might be okay. See the chart & discussion midway down this page Having RS232 or RS485 driver would not hurt.

Does using RS232 with max232 needs any code change or special library or just connect the max232 to TX RX GND?? I mean if I already able to send data between two arduinos using TX RX GND but I need longer distance communication.

The MAX232 is just buffering signals, no code changes needed. The chip changes the uC's Tx 0/5V output to ~+10v/-10V to send down the wire, on the receive side the chip changes the +10V/-10V back to 0/5V to drive the uC's Rx pin. So you need a MAX232 on each end, and five 0.1uF caps, or 1uF caps, depending on which driver you get, for each chip to make the +/-10V for the driver.

this is exactly what I know. Thanks for ensuring me :)

I can use RS-485 with max485 the same way as max232. right?

Yes. Be sure to use termination resistors.

Scott Baker:

50ft is the standard "limit" for RS232 (the +/- 10Volt level) granted you can acheive longer distances with slower baud rates and careful routing/shielding. You will not be 100% successful with that length @ 0-5Volt levels (I've read that even 10ft can be troublesome at high baudrates). Definitely go with RS232 or RS485. It's very cheap to implement. Or you can experiment with the 0-5V, but it may get frustrating with intermittant issues.