Tech Directions - February 2009 - (Page 20) Photo 2 1M Do not attach the switch at this time. 3. Get the 8-pin DIP socket, then, referring to Fig. 1, carefully determine where the 8-pin socket will be inserted into the perfboard. Locate where each individual pin of the 8-pin socket will be inserted. Mark these at the left, next to the PB switch. Referring to the panel layout drawing (Fig. 1), insert the two LEDs. As viewed from the outside of the panel, make sure the flat sides A 5 4 8 1 A 470 470 0.1 μ 20 techdirections ◆ FEBRUARY 2009 1K functional and lab worthy, you will PTT TIMER construct the 555-timer checker that looks like the unit shown in Photo 2. But do not disassemble your protoboard circuit. If there is a wiring error in your newly built 555-timer Fig. 2—Front panel drawing checker, having a unit that works will prove very helpful. Now, let’s get startof the right LED. Solder ed! 3.2 a piece of #24 AWG bare 1. Refer to the panel Drill with #54, 8 places wire between pin 1 of layout drawing (Fig. 1). C the 8-pin DIP socket and Carefully measure and C the push-button switch’s mark the perfboard 0.8 pin closest to the DIP according to the in0.8 socket. Use #24 AWG dicated dimensions. bare wire to connect Double-check your 2.0 A pin 8 to pin 4 and pin 6 measurements, then 0.6 B 1.5 to pin 2 of the 8-pin DIP carefully cut the perf1.05 0.9 1.0 socket. Referring to Fig. board. Place the cut C 3, complete the hookup perfboard on top of the C 0.25 of the timer-checker’s plastic box. It should fit Typical, circuit. nicely. If not, fix it. Use A hole—Drill with #J each B hole—Drill with #54 All numbers 8. Get the battery a piece of medium-grit corner C hole—Drill with #30 are in inches clip. Referring to the sandpaper to smooth schematic diagram (Fig. out any rough edges on Fig. 1—Panel layout drawing 4) and the assembly the perfboard’s edges. 2. Next, carefully be orientated so that its measure and mark the location of the Fig. 3—Wiring diagram two pins are horizontally hole to be drilled in the perfboard positioned. Use your for the push-button switch (PTT) as fingers to snug the hexshown on the front panel drawing nut down. (Fig. 2). Recheck your measurements, 6. Referring to Fig. 2, then carefully drill the hole using a #J insert the 8-pin socket drill bit. If you do not have a #J drill into the perfboard. Make bit, use a drill bit that will allow a Red Blk sure that the indent is 1/4" thread to pass through the hole. 0.25 locations with a pencil. Use a #54 drill bit to drill the eight holes. Insert the 8-pin socket into the perf-board. The socket should fit snugly. Do not mount the 8-pin socket at this time. 4. Determine the locations where the four mounting screws will be inserted through the perfboard and attach to the plastic enclosure. Using a pencil, mark each location. Double-check your measurements. If all is OK, drill the holes using a #30 drill bit. 5. Attach the push-button switch to the perfboard. The push-button switch should of the LEDs (cathodes) are opposing—the left LEDs flat side down and the right LEDs flat side up. 7. Referring to the wiring diagram (Fig. 3), carefully solder the leads of resistors R3 and R4 to pin 3 of the 8pin DIP socket. Solder the other lead of R3 to the cathode of the left LED and the other lead of R4 to the anode 555 Timer Checker Vlo Vhi
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