Introduction.
We have completed the development of a 4-channel 8-bit analog to
digital converter which may
be easily interfaced with either a Basic Stamp 1 or Basic Stamp 2. It
consists simply of a single
programmed Microchip PIC12C671 8-pin DIP.
It may also be interfaced with a PC com port or similar using a DS275
RS232 transceiver which is
also packaged in an 8-pin DIP.
Description of Operation.
Normally, the PIC is in a sleep mode. A momentary logic zero on the
/GO input causes the PIC
to reset, pause for 250 msecs, perform an A/D conversion on each of the
four input channels,
sending the result at 9600 baud on output SER, and the PIC returns to its
sleep mode.
The results of the four measurements are returned to the Stamp or PC in
hexadecimal format;
FE 3C 22 1D
Note that the quantities are separated with a single space. The line
is terminated with a new line
consisting of a carriage return and line feed ($0D, $0A).
BASIC Stamp Interface.
Thus, in the case of the Basic Stamp, the interface is simply one of
winking a lead low and then
reading the result.
OUT1=0 ' bring the /GO lead momentarily low OUT1=1 SERIN 0, 84, 1000, TM_OUT, [HEX Q_0, HEX Q_1, HEX Q_2, HEX Q_3]
This design provides the enthusiast with a great deal of power with
minimal effort; a single 8-pin
DIP and three lines of code.
PC Serial Interface.
In interfacing with a PC, a DS275 transceiver is required. This is an
8-pin DIP that converts
RS232 levels to TTL and TTL to RS232. Unlike the MAX232 no external
capacitors are
required.
To initiate a measurement sequence, the PC need only send any character
which pulls the /GO
input low and the data is returned in the above format.
Note that the voltage on any of the channels may be calculated as;
V_CH = Q / 256 * V_ref
where V_ref is the +5.0 Volt supply.
Pricing.
Stamp Evaluation Kit ($10.00). Includes two programmed 4-channel A/D
PICs, logic probe and
documentation.
PC Evaluation Kit ($16.00). This is the same as the Stamp Evaluation
Kit plus two DS275
Transceivers.
Additional Programmed PICs - $3.50
DS275 Only - $3.00