RF Data Modems

[JasonS]

I was wondering if there is anyone who has ever attached the RS-422 radio modems we have gotten in the kit for the past three years, directly to a Basic Stamp? I am working on a research project that requires two robots to communicate and my team (go HeatWave!) has some old modems that I'm gonna borrow. Specifically, I would like to attach the modems to two BS2SX chips (the same ones the RC uses) in order for them to communicate. If anyone has any information on how I might be able to do this, or even pin outs for the Screamer RS-422 would be very helpful.
Thanks a lot!

Jason Schuler

[rbayer]

NO! The Basic Stamps (all variations including SX) only support 232. If you want to use the 422 modems, you will need to convert the 232 signal from the stamp to a valid 422. From what I've heard this can be done very easily but is somewhat expensive. Anyway, if you get regular 232 wireless modems (like the debugging ones), it should work just fine.

The commands you will need are:
shiftin/shiftout (syncronous I/O)
serin/serout (async I/O)

Note that any pins on the stamp can carry a 232 signal and any of the pins can be used for clocking.

--Rob

[JasonS]

Actually I think you can just use a 232 to 422 converter (part # DS75176B, $1.06ea. I believe) to allow the stamp to talk with the modems. You are right though, the stamp cannot talk directly with the modem...sorry, I should have clarified that. I would like to use the 422s because I have them and it would cost me virtually nothing, whereas the 232 modems would cost significantly more than I have. Thanks!

[rbayer]

That should work. Somebody in a previous thread had said $80 so I was a bit skeptical about the cost-effectiveness of your plan. Anyway, if you can get them for $1.06 I see no reason why it wouldn't work just fine.

[Sean Conway]

Originally posted by JasonS
Actually I think you can just use a 232 to 422 converter (part # DS75176B, $1.06ea. I believe) to allow the stamp to talk with the modems.

I'm not familiar enough with the stamp to be sure of it's architecture, but I thought I'd post this anyway.

The DS75176B is a line transceiver, which converts from ttl levels (+5v) to line levels (+15v/-10v). It is an IC which must be connected to the stamp, not a module of any sort.

It requires logic lines other than the serial i/o to control it. Make sure you know what you're doing before you connect anything up, else the stamps may go poof.

Hope this helps.

[Dave Flowerday]

In a pinch, we made an RS232 to RS422 converter for use with the radio modems from a MAX232 and MAX488. From Digikey, the MAX488 is $2.81and the MAX232CPE is $3.31. Assuming the Stamp uses TTL levels on it's data lines, you'd just need the MAX488. However, it's not as simple as just building the converter and replacing a serial cable with the modems. The Screamer422 modems that are provided as part of the FIRST kit only support one of Ewave's data modes, which is called RM2000 and was specifically designed for the robotics competition. What that translates into is that the Screamer422 modems will only transmit data 26 bytes at a time. So, depending on what you're using them for they may or may not work. Also note that these models don't pass RTS/CTS or any other control lines, just the TX and RX data.

[Dave Flowerday]

Originally posted by JasonS
If anyone has any information on how I might be able to do this, or even pin outs for the Screamer RS-422 would be very helpful.

By the way, you can get the data sheets including the pinouts on the Screamer422 from http://www.electrowave.com.