You've put your money into parts, you don't want to fry them by hooking them up to a cheap power supply circuit, do you? I didn't think so. That's why there are a few more components to the power supply than would be necessary with a lab power supply.
First, the 11DQ10 diode keeps negative voltages away, the metal oxide varistor dissipates surges on the power line, and the P6KE18CA also limits the voltage to a range the regulator can handle. The regulator is a LM2940CT-5.0, which is pin compatible with the 7805, but was designed for automotive use. It can withstand voltages of 40-60 volts (load dump, which happens when you disconnect the battery or the alternator goes bad), negative voltages, etc. You can economize on some of these parts, but I'd rather not take a risk and be on the safe side. If you have comments on the power supply design, I'd really like to hear them!
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