XBee and Sensor Printed Circuit Board

After finishing the Building Wireless Sensor Networks book, I have to look at the output of the circuits and realize that you cant deploy a solder-less breadboard. (Laugh) It doesn’t look very professional to ship someone a rats nest of wiring. So I bought a copy of Eagle CAD PCB Design Software and created a printed circuit board(PCB). Check it out:

Uploaded this design to OSH Park PCB Manufacturer. As you can see from the pictures, they use a distinctive purple solder mask. At about $5 a square inch, three copies of this board cost ~$45 dollars and about two weeks to get the boards back.

There are four PCB’s on this one board. Three temperature sensor PCB’s and one main PCB holding a 3.3V Voltage Regulator and an XBee. On the main PCB I pulled out the RSSI and ON pins through LED’s that can be enabled by a jumper. Pulled out the RX/TX and CTS/RTS wires for future expansion. And provided VCC and 3.3V pins for testing and for powering the board if needed without using a wall plug.

My plan is to have this one XBee board read three temperature sensors.  This will replace the three XBee boards each reading a single temperature sensor that I currently have. I’m rewriting the BWSN Chapter 8 “More to Love” Processing sketch to read these three analog values and upload to Xively.

So what went right:

* (MAJOR) Wrestled with Eagle CAD to create my first PCB.

* (MINOR) Ordered the correct matching Molex male/female and crimps to have a polarized connectors for the voltage and data pins from the XBee board to the Temperature sensor. You may not think this is important but having a connector that only allows a certain orientation to be plugged in saves time and effort in troubleshooting.

What went wrong:

* (MAJOR ISSUE) Used the wrong Voltage regulator part in Eagle CAD. The one I originally used on this board was center grounded:

Pin 1(VOUT) Pin 2(GND) Pin 3(VIN)

But the LD1117V33 voltage regulator in To-220 package I’m using is Pin 1 grounded:

Pin 1(GND) Pin 2(VOUT) Pin 3(VIN)

Dang. So a small hardware mod when connecting this to the board and its all fixed! But it’s kind of frustrating to solder the part onto the board, test and find that you aren’t getting 3.3v out.

Overlooked Label* (MINOR) Forgot to add (Plus)+ and (Gnd)- text on the PCB silkscren pins for the VCC and 3.3V taps I placed on the board.

Crowded Text* (MINOR) Need to move the 3.3V-GND-DATA labels on the PCB silkscreen out from the pins so that the Molex connector doesn’t completely obscure the text.

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