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Xport-to-PIC printed circuit board

  
This page details a printed circuit board I designed to interface an Xport to a 28-pin PIC microcontroller. I've tested it with the 18F252, but presumably it will work with any 28-pin PIC with the same pin assignments. The board is designed as a module for integrating the Xport with sensors and simple actuators through the PIC.

The PIC onboard is connected to a 24-pin connector so that all of its I/O pins, and ground and 5V, can be connected to external devices. It's also connected to the Xport's RX, TX, configurable I/O, and reset pins via two sets of jumper terminals. There is also a connector to allow for in-circuit serial programming of the PIC.

In addition to the PIC, the board also has a MAX3323 3.3V TTL-to-RS-232 converter, to connect the Xport to an RS-232 serial port. The MAX3323 both inverts the TTL serial signals and adjusts the voltages to RS-232 levels.

Here's a schematic of the board. The image is large. Following are images of the top of the board and the bottom:

Top of board

Bottom of board

And here's a picture of a finished board:

The jumpers are as follows:

Jumper
Function
JP1 Connects Xport and PIC serial ports, in the following sequence (upper to lower in the photo above):
Xport pin: PIC pin:
RX RC6
TX RC7
JP2 Connects PIC I/O pins to external devices, as follows upper to lower and left to right, as in photo above):
RA0 RA1 RA2 RA3 RA4 RA5 RC0 RC1 RC2 RC3 RC4 Ground
RB7 RB6 RB5 RB4 RB3 RB2 RB1 RB0 RC7 RC6 RC5 +5V
JP3
Connects PIC pins to Xprt I/O and reset pins, in the following sequence (upper to lower):
Xport pin: PIC pin:
CP3 RC3
CP2 RC2
CP1 RC1
reset RC0
JP4

Connects Pic to In-Circuit serial programmer. Pins used (left to right) are:

+5V ground reset RB7 RB6 RB3

If you're looking to fabricate a version of this board yourself, the gerber files are here. I made the original document in Eagle CAD, and orderd my boards from Advanced Circuits. You can also get boards made cheap by Sparkfun (tell them I sent you).

I got the components for my board from Newark and Digikey; here are the part numbers:

Part Value Part No. Comments
C1 10uF Digikey P828-ND Any polarized 10uF capacitor will do.
C2 1.0uF Digikey 478-1836-ND Any polarized 1.0uF capacitor will do.
C3 1.0uF Digikey 478-1836-ND Any polarized 1.0uF capacitor will do.
C4 10uF Digikey P828-ND Any polarized 10uF capacitor will do.
C5 22pF Digikey 399-1890-ND Any 22pF capacitor will do.
C6 22pF Digikey 399-1890-ND Any 22pF capacitor will do.
C7 0.1uF Digikey 399-2127-ND Any 0.1uF capacitor will do.
C8 0.1uF Digikey 399-2127-ND Any 0.1uF capacitor will do.
C9 0.1uF Digikey 399-2127-ND Any 0.1uF capacitor will do.
C10 0.1uF Digikey 399-2127-ND Any 0.1uF capacitor will do.
C11 0.1uF Digikey 399-2127-ND Any 0.1uF capacitor will do.
C12 0.1uF Digikey 399-2127-ND Any 0.1uF capacitor will do.
C13 0.1uF Digikey 399-2127-ND Any 0.1uF capacitor will do.
D1 1N5226B-T Newark38C7685
Digikey 1N5226BDICT-ND		 These limit the input voltages on the input pins to 3.3V. DO-35 package
D2 1N5226B-T Newark38C7685
Digikey 1N5226BDICT-ND		 These limit the input voltages on the input pins to 3.3V. DO-35 package
D3 1N5226B-T Newark38C7685
Digikey 1N5226BDICT-ND		 These limit the input voltages on the input pins to 3.3V. DO-35 package
D4 1N5226B-T Newark38C7685
Digikey 1N5226BDICT-ND		 These limit the input voltages on the input pins to 3.3V. DO-35 package
D5 1N5226B-T Newark38C7685
Digikey 1N5226BDICT-ND		 These limit the input voltages on the input pins to 3.3V. DO-35 package
D6 1N5817 Newark 48F6702
Digikey,1N5817DICT-ND		 This keeps the 3.3V regulator from overheating. DO-41 package
IC1 MIC29150-5.0BT Newark 83F5901 Make sure to use the BT model for this part. There is a BU model, which is a surface mount part that doesn't match this board.
IC2 MIC2915033-BU Newark 83F5900 Make sure to use the the BU model, which is a surface-mount (TO-263) package. The two different packages help differentiate the 5V regulator from the 3.3V regulator.
J1 Pin Headers Digikey A1920-ND These are just male straight or right-angle pin headers, 0.1-inch spacing. Get them from any electronics retailer.
J2 Pin Headers Digikey 929974-01-36-ND (Buy 2, one for each row) I usually use female pin headers on my boards for this connector, but you can use male if you prefer. Get them from any electronics retailer.
J3 Pin Headers Digikey A1920-ND These are just male straight or right-angle pin headers, 0.1-inch spacing. Get them from any electronics retailer.
J4 Pin Headers Digikey A1920-ND These are just male straight or right-angle pin headers, 0.1-inch spacing. Get them from any electronics retailer.
J1, 2, 4 Jumper connectors Digikey S9000-ND (buy 10) These are shorting blocks that connect the jumper pins.
Q1 Clock crystal Digikey X195-ND I use a 20MHz clock, but you can use any clock that fits.
R1 10K Newark 84N2322
Digikey 10KQBK-ND 		these go with the zener diodes. 0207/10 package
R2 10K Newark 84N2322
Digikey 10KQBK-ND 		these go with the zener diodes. 0207/10 package
R3 10K Newark 84N2322
Digikey 10KQBK-ND 		these go with the zener diodes. 0207/10 package
R4 10K Newark 84N2322
Digikey 10KQBK-ND 		these go with the zener diodes. 0207/10 package
R5 10K Newark 84N2322
Digikey 10KQBK-ND 		these go with the zener diodes. 0207/10 package
U1 PIC Microchip PIC18F252/I-P Use any 28-pin DIP model PIC
U1 28-pin DIP socket Digikey ED5328-ND This allows you to remove the PIC instead of soldering it directly to the board.
U2 X-PORT Symmetry XP1002000-03 I get mine from Symmetry, but you can also get them from GridConnect (thanks to Jeff Gray for the link)
U3 MAX3323 Maxim MAX3323-EEPE Maxim will sample these for free in small quantities
U3 16-pin DIP socket Digikey ED5316-ND This allows you to remove the MAX3323 instead of soldering it directly to the board.
X1 DB9 Serial connector Digikey A2100-ND Female serial connector
X2 DC power jack Digikey CP-202A-ND This is a 2.1mm ID, 5.5mm OD jack, wired so that the center is positive. 8 - 15V DC input, at least 500 mA.

As always, I recommend soldering the passive components first (resistors, diodes, connectors, capacitors) and the active components last. The only exception to this is that I usually solder on the voltage regulators and power connector at the start, then connect power and measure for the appropriate voltages across the power and ground connections of the PIC connector, the Xport connector, and the MAX3323.

Once you've got the hardware connected, you're ready to move on to configuration.

Note; I don't warrant this board in any way. use at your own risk. assembled properly, it works fine, but this design is not certified for commercial or industrial use in any way. It is copyright Tom Igoe, 2004