TAP-28 - A “throw away” PIC board - TAP-28 Building

Written by Jon Chandler

Published on 11 February 2010

Page 6 of 14

TAP-28 Building

For a given application, some components on the TAP-28 board may not be needed. For a board dedicated to a particular project, this will further reduce its cost. The blocks below indicate the function of various components.

The Microprocessor
U1 C1, C2 C3 R1 Y1	28 pin microprocessors with a pinout similar to the PIC18F242 may be used on this board. A socket may be used if desired. A 20 MHz crystal is the usual choice, with C1 and C2 being 22 pF. C3 is a bypass capacitor of 0.1 µF. R1 pulls /MCLR high. This is the minimum compliment of parts to use the TAP-28.

Power
J10 J11	The TAP-28 board requires a regulated 5V (or possibly lower) power supply. J10 may be installed to use a USB cable for power. *Note: If the underside of J10 is conductive, insulate the area above J11 with electrical tape to prevent shorts.* Alternatively, a terminal block may be soldered in the J11 position or leads from a power supply connected to the J11 position.

ICSP
J3 S3 (optional)	ICSP is the simplest way to program the TAP-28. J3 is pinned out for use with the PICkit and many other ICSP programmers. S3 is optional to reset the microprocessor by pulling /MCLR low.

The LEDs
LED1, LED2 LED3, LED4 R3, R4, R5, R6	LEDs 1 -4 are T1 3mm LEDs. *The anode(+) side should be installed toward the edge of the board.* The resistors are current limiting resistors for the LEDs. Shorting JMP1, JMP2, JMP3 and JMP4 with solder connects the LEDs to the circuit.

The Switches
S1, S2 R7, R8	S1 and S2 may be used as desired for program control and input. R7 and R8 are pullup resistors for these switches. Shorting JMP5 and JMP6 with solder connects the switches to the circuit.

UART Connector
J9 R12	The UART connector may be used for TTL-level serial communications or for general purpose use and it connected to the PIC’s hardware USART. The pinout matches the PICkit 2 UART tool. R12 is a pullup resistor connected to Port B1 and pin 1 which may be useful for handshaking. Short JMP10 to connect it to the circuit.

J1 & J2
J1 J2	J1 and J2 are normally female headers used to connect a daughter board to the TAP-28. They are also useful to make jumper connections to a solderless breadboard from the TAP-28. All port pins are available on J1 & J2.

3 Pin Jacks
J4, J5, J6, J7 C4	These jacks may be used for analog input (J4, J5), PWM output (J6, J7), servos or general I/O. C4 is recommended if servos are connected to prevent voltage transients.

I2C/SPI
J9 R9 R10 R11	J9 is connected to the PIC’s Master Synchronous Serial Port (MSSP) module for I2C and SPI communications. R9 and R10 for pullup resistors for the I2C SCL and SDA lines. R11 is a pullup resistor which may be used for an interrupt line. This connector may also be used as 4 general purpose I/O pins. The pullup resistors are connected to the circuit by the adjacent solder jumpers.

Parts List

The following typical values are suggested but personal preferences and the application may dictate other values.

Part	Value	Comments
C1, C2	22 pF, 5%, 50V	Ceramic disk, 0.1" lead spacing
C3	0.1 uF, 20%, 50V	Ceramic disk, 0.1" lead spacing
C4	10 uF, 20V	Tantalum or electrolytic, 0.2" lead spacing
R1, R7, R8, R11, R12	10k, 5%, 1/8w
R3, R4, R5, R6	301, 5%, 1/8 w	depends on LED parameters
R9, R10	4k7, 5%, 1/8w	I2C pullup
J1, J2	15 pin female header	0.1" lead spacing
J3, J8, J9	Molex 22-23-61 6 pin hdr	0.1" lead spacing. Standard header pins may be used.
J4, J5, J6	3 pin header	0.1" lead spacing
J10	USB B, full size	pinout appears to be universal
J11	Terminal block	0.2" spacing, optional if J10 not used
LED1, LED2, LED3, LED4	LED, T1 3mm	Color as desired. Max current is 20 mA
S1, S2, S3	Tactile switch	6 mm SPST mom, Omron B3F-10XX series or similar
U1	PIC 18F2420 or similar	28 pin PIC 18F series, 18F242, 18F252, 18F2420 or similar (0.3" wide DIP)
Y1	20 MHz	20.000 MHz HC49/US (low profile)

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