Tech Directions - December 2007 - (Page 17)

teries, then place a piece of folded cardboard between them. This will keep the batteries from moving around inside of the box with the lid in place. Place the perfboard on top of the box. Insert the four mounting screws through the mounting holes of the perfboard and tighten the screws. You can spiff up the appearance of the op-amp checker by applying labels to indicate what the instrument is, identify the panel parts, and indicate the location of pin 1 of the 8-pin DIP socket. This will make the op-amp checker more functional and professional looking. You can use labels with adhesive backs, your word processor, scissors, and a razor knife to create these decals. Clear tape over white paper with hand-printed letters also works quite well. Using the Op-Amp Checker Whether using the op-amp checker constructed on your protoboard or the one in the enclosure, the testing procedure will be the same. Get a good 8-pin op-amp. Make sure that the op-amp’s leads are straight. Insert the op-amp in the 8-pin DIP socket. (Pin 1 of the opamp must be inserted into the correct location or it will not work.) Once the op-amp is correctly inserted in the 8-pin DIP socket, the two LEDs should toggle when you press the PTT switch. The most common problem experienced in using the op-amp checker is a bent pin on an op-amp, which is produced when the user is not careful while attempting to insert the op-amp into the 8-pin DIP socket. Gather several different types of op-amps and test them. When testing different types of op-amps, you will note a difference in the LED’s toggle rate. This is because each opamp type most likely has a different slew rate. For example, an LM741 op-amp will have a flash rate that is slower than an LM301 op-amp. An LM318 op-amp will toggle quite rapidly because of its high slew rate. A good rule of thumb: The higher the slew rate, the greater the op-amps’ bandwidth. You’ll find that the batteries will last a very long time. The unit does not turn on until the user plugs an op-amp into the test socket and pushes the PTT switch. Conclusion Whether you are a student or an instructor, this handy op-amp checker can be of great use to you. It will allow you to check and/or test op-amps at the proto-board stage, and, with a little experience, you will be able to estimate slew rates. This can be handy if you need an amplifier circuit to have a wide bandwidth. Note that only op-amps having an 8-pin standard pin-out will work in your op-amp checker. Many devices are housed in an 8-pin package (e.g., timers, comparators, dual op-amps, consumer devices). And be careful— IC chips can get hot and burn your fingers. Happy checking! And if you discover anything interesting, let me know via e-mail. www.techdirections.com ELECTRICITY/ELECTRONICS 17 http://www.testequipmentdepot.com http://www.testequipmentdepot.com http://www.techdirections.com

Table of Contents Feed for the Digital Edition of Tech Directions - December 2007

Tech Directions - December 2007 Technically Speaking Contents Direct from Washington The News Report Technology Today Technology's Past Mastering Computers Is This Op-Amp Any Good? Lab-Built Checker Removes All Doubt Here Comes the Sun! Residential Solar Systems Add Up to Savings Pinhole Cameras—For Science, Art, and Fun! Poster Project Maps Out Design Process Gifts for Geeks E-gallery More than Fun

Tech Directions - December 2007

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