Photo 1. The development and control system.
Photo 2. There isn’t much to the interface.
run off a 4 MHz clock. Using this clock, instructions will be
processed at 1 MHz, per Microchip’s datasheet. The PC-to-R/C
circuit will receive input on Port B (Figure 5, pins 7 through
13) of the PIC16F84, from the PC’s parallel port. Code for
the PIC is written in C and compiled with the PICC PCM
compiler from CCS, Inc. ( www.ccsinfo.com). The device
programmer used was the PIC16PRO. The PICALL software
was used to burn hex code to the PIC. Both are available from
Amazon Electronics ( www.electronics123.com).
Figure 6 is a schematic of the PC-to-R/C circuit. A list of
parts is given in Table 1. All parts can be purchased from
Digi-Key ( www.digikey.com). The part numbers and prices
are provided. The AC adapter and AC adapter connector are
an optional method of providing 5 VDC power to the circuit.
Free samples of the PIC16F84 can be ordered from Microchip
Port B on the PIC16F84 (pins 7 through 13) connects
to data pins D0 through D7 on the parallel port (pins 2
through 9). The STROBE line of the parallel port (pin 1)
connects to the PIC16F84 at RA0 (pin 17) through a 1K Ω
pullup resistor. The parallel port’s BUSY line (pin 11)
connects to the PIC16F84 at RA1 (pin 18). Line 19 from the
parallel port is grounded. Output is sent to the buddy
box from the PIC16F84 at RA3 (pin 2). The remaining
connections on the PIC16F84 are for the clock, power, and
Part placement is not critical and you can solder or
wirewrap the circuit in an afternoon. Alternately, you can
etch a PCB using the artwork provided in Figure 7. Notice
that the diameters of the leads for the six-pin DIN, 25-pin
connectors, and power adapter jack are larger than typical
pin sizes and require slightly larger drill diameters.
In addition to the circuit, you must write the code. The
overall sequence of operation is as follows: First, a program
running on a PC writes data to the parallel port. This data
reaches the PC-to-R/C circuit, which houses the PIC16F84
Second, a program running on the PIC16F84 transforms
the incoming data into a frame of PWM signals that is
uploaded into the R/C transmitter’s buddy port. Together,
the circuit and code allow a PC-based program to remotely
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SERVO 07.2004 75