Issue
160 November 2003
RF
Made Simple
RESULTS
The
final prototype of the easy-Radio/CH2124 modem station
is shown in Photo 5. Adding the data rate converter
took a bit of the “easy” out of the design, but, as
you can see in Listing 1 and Figure 1, not much of the
simplicity was destroyed, because the code and circuitry
of the data rate converter is minimal.
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(Click
here to enlarge)
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Photo
5—The nine-pin gender changer connects the easy-Radio’s
MAX202 to the iModem evaluation board’s MAX237.
After all of the development and debugging is done,
the easy-Radio, PIC12F675, and CH2124 are the only
components needed (in addition to power and a phone
line) to generate an e-mail using the embedded RF
link. |
| Listing
1—Most of the work is done by the Custom Computer
Services C compiler. The Custom Computer Services
C Compiler Project Wizard generated 99% of the set-up
code. I used two serial streams and wrote only three
itty-bitty lines of C source code to turn the itty-bitty
PIC into a data rate converter. |
|
(Click
here to enlarge)
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Figure
1—I simply inserted the PIC12F675 between the easy-Radio’s
19,200-bps serial data-out line and the MAX202 RS-232
converter IC’s TTL-side transmit pin. The PIC12F675
does no buffering and dumps out the data rate-converted
data as soon as it gets it. Character pacing is
handled by the remote sending easy-Radio, because
it’s going from a faster to a slower data rate. |
As
I worked on this project, I purposely tried to avoid
designing additional support hardware, because the products
I used were supposed to make an RF-challenged (or communications-challenged)
product design engineer’s life easier. I think the point
has been proven, because both products were literally
ripped out of their boxes and thrown into service without
performing any kind of configuration or setup. It cannot
get any less complicated and more embedded than that.
