Interfacing the RTX-12 Modem to a BASIC Stamp
Wireless Communication for Microcontrollers using HT Radios
The Tigertronics (www.tigertronics.com
) RTX-12 Radio Modem and a set of 2-meter handheld radio transceivers offer a functional solution for long-range data transmission between microcontrollers. With 5W power on standard 2-meter handheld radios it is quite·
easy to send data several miles or many more depending on antennas and line-of-sight, and whether or not repeaters are used. In this project we were able to send and receive valid data packets at a distance of three miles using 5W radios and HT antennas.
You must have an Amatuer Radio License (available through www.arrl.org
) to try this project, though you could also attempt the same using the Family Radio Service radios if they have mic/speaker connections.
This example uses the BASIC Stamp, though it may be substituted with any microcontroller. The example includes two sets of programs: a simple version that lacks error checking and a more complete example with checksums.
The reason I am experimenting with this project is because I plan on porting it to the Propeller for use in my outdoor robots for telemetry. Specifically, this platform: http://forums.parallax.com/showthread.php?p=654636
- (2) RTX-12OEM Radio Modems (Tigertronics #RTX-12OEM)
- (2) BASIC Stamp 2 Modules (Parallax #BS2-IC)
- (2) Super Carrier Boards (Parallax #27130) or other project area
- (2) Amateur Handheld Transceivers (Yaesu #VX-6R used in this example though a variety of HT models are suitable)
- (2) Radio Adapter Cables (Yausu #CT-91 for the above radio)
Use the same schematic for transmitter and receiver. The receiver BASIC Stamp will be connected to your PC for DEBUG.·
Below are some general suggestions about the hardware setup:
Example PBASIC Programs
- Two duplicate setups are required to run the sample programs; the schematic is the same for the transmitter and receiver. The receiver will remain connected to the PC via serial or USB cable to display data from the transmitter.·
- Tigertronics offers a ribbon cable to easily connect to their RTX-12. We suggest you purchase this cable since connecting to the RTX-12’s individual pins can be difficult without it. Tigertronics provides only one end of this cable terminated with the connector. You will need to locate some female 2x5 IDC connectors to wire the cable to your microcontroller.
- 2-meter HT radio manufacturers have vendor-specific cables to connect the mic and speaker port. The mic is commonly a 2.5mm cable and the speaker is 3.5mm. These are often joined for a single connection to the radio.
- You will need to make a cable to connect the radio’s mic and speaker cable to the microcontroller project board. These are both mono cables, available from RadioShack and other electronic suppliers.
- Critical attention should be paid to wiring. Diagnosing problems between the modem, radio and BASIC Stamp can be quite tedious if mistakes are made to the wiring.
- Tune both of your radios to the ARRL’s 2-meter “miscellaneous and experimental modes” of 145.50-145.80 (MHz). Set your radios to the lowest power mode necessary for transmitting and receiving.
The RTX-12 Simple Transmit.BS2 and RTX Simple Receive.BS2 programs have no checksums or other error checking built into them. They are only provided to check your setup. To test them, program one setup as a transmitter and disconnect. Program the other setup as a receiver and leave it connected to the PC. Press "reset" on the transmitter and the receiver should display the following in the DEBUG window:
The RTX-12 Transmit.BS2 and RTX-12 Receive.BS2 programs have a 16-bit checksum to verify data integrity. These programs are documented for ease of use. You can simply change the data in the EEPROM to send different strings or values.
Resources and Downloads
- RTX-12OEM modem documentation from Tigertronics web site www.tigertronics.com
- American Radio Relay League web site www.arrl.org for licensing and band plan
- Example BASIC Stamp 2 Source code (in this post, zipped)
-·Full demo source code RTX-12 Transmit.bs2 and RTX-12 Receive.bs2
-·Simple demo source code RTX-12 Simple Transmit.bs2 and Simple Receive.bs2
- Amateur radio equipment reviews on eHam.net http://www.eham.net/reviews/
Chris Savage helped significantly by writing the complete code example and debugging the hardware. John Olson from Tigerbotics provided a quick review of my project for accuracy, too. Jim Ewald (IT Guy) on the forums is an experienced·
ham operator and was most helpful in the tests we conducted at Parallax. Jim recently set up a ham station and antenna on the roof of our building so you'll probably see more radio projects from us in the future.
Post Edited (Ken Gracey (Parallax)) : 10/23/2008 4:33:04 PM GMT