birt barcode tool A CONSTRUCTION TECHNIQUES in Font

Create QR Code in Font A CONSTRUCTION TECHNIQUES

After building the circuit, you ll need to make sure that it works. While running a program that configures the port as an old RCX type Light Sensor, check that the voltage across C1 is between 9V and 6V. You can add a potentiometer, as in Figure A-4, to input a known voltage.

Using a voltmeter and a program that reads the Raw sensor value, you can create a plot like Figure A-5. The lower end of the voltage range has a flat region because the LM324 cannot output a value less than about 0.6V.

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Figure A-5. Voltage input versus Raw value plot You could just leave the circuit on the breadboard for as long as you needed it, but it s better to commit it permanently to a PCB. It will be more compact and much more reliable because it keeps parts from accidentally being pulled out of the breadboard.

The Global Specialties Experimenter PCB or the Radio Shack 276-170 (see Figure A-6) match the layout of the electronic breadboard exactly, as can be seen in the bottom view in Figure A-7. It has the same row and column markings as the breadboard, so it should be easy to transfer the parts from the breadboard to the PCB. The only problem with the PCB is that it s way too long. That means that one Experimenter PCB could be the source for several sensors.

Figure A-7. Bottom view of the PCB Cutting the PCB is a lot easier than you might think: you need only a straight-edge ruler and a sharp knife, as shown in Figure A-8. You score the board by creating a shallow groove in the top and bottom of the board along a column of holes where you want to cut the board. Once the board has been scored, it will snap by bending it at the groove.

Figure A-8. Scoring the PC board Start by laying the straight-edge ruler along the column of holes where you want to cut the PCB. Take a sharp knife and run it along the straight edge of the entire width of the board. The knife will bump along from hole to hole. At first, don t use very much pressure. Keep running the knife along exactly the same path over and over until a groove develops. It usually takes about ten passes. Repeat the process on the bottom side of the board. Bracing your thumbs at the groove, as shown in Figure A-9, gently bend the board down on both sides with your fingers. It should snap with only a reasonable amount of force. If it doesn t snap, continue to cut at the grooves to make them a little deeper and try again. You ll be left with a small PCB that s just the right size for your project.

As you cut away other small PCBs, you ll notice that the printed column numbers no longer match the solderless breadboard. The original painted numbers are easily scratched off, and you can re-mark them with permanent marker.

Soldering the parts to the PCB is probably the scariest part. It requires a certain amount of skill, but after a few connections you ll find that it really isn t that difficult. Making good solder connections requires following a few basic rules: The soldering iron should be a 25-to-40-watt pencil type with a 1/8"-to-3/16" chisel- or coneshaped tip. Always wait at least five minutes for the soldering iron to come up to temperature. The solder should be rosin core 60/40 tin/lead content with .062" diameter. Never use acid core or the type used for plumbing.

Caution Lead is a poison and has been proven to cause health problems, especially for young children. Never