Nuts and Volts - January 2009

■ FIGURE 8

■ FIGURE 9

but you should tighten everything.)

■ FIGURE 10

Testing

residue and examine the board for missing or bad solder connections; fix any bad ones.

The final step in construction is to add the two “legs.” For the Proto Buddy to be level with the SBB, two aluminum, male/female, 4-40 threaded hex standoffs are required: one in each of the two corner holes on the PCB board as shown in Figure 8. Note the nylon screw used to prevent scratching when the Proto Buddy sits on a table. (The hardware in Figure 8 is shown loose,

■ FIGURE 11

Mount the Proto Buddy to a

■ TABLE 1 solderless breadboard by inserting the three sets of mounting pins into the contact strip on the edge of the SBB (refer to Figure 4). Connect a 9V battery to the terminal block (also shown in Figure 4). Cut six four inch pieces from a roll of 22 guage solid insulated hook-up wire. Strip off about 1/4 inch of insulation from both ends of each piece. Insert one end of a wire into the pin jack connected to the positive (+) side of the battery and connect the other end to one of the LED pin jacks marked with ‘j.’ Use another piece of wire to connect one of the S1 pin jacks to the L1 pin jack marked with ‘C.’ Use another piece of wire to connect one of the S2 pin jacks to the L2 pin jack marked with ‘C.’ Use two pieces of wire to connect the other pin jacks of S1 and S2 to a single connector strip on the SBB. Use a piece of wire to connect the same connector strip to the pin jack that goes to the negative (-) side of the battery.

Figure 9 shows the circuit you just built. As you operate S1, L1 should go on and off. Likewise, as you operate S2, L2 should go on and off. Once you verify the circuit works, rewire it to use S3 and S4 instead of S1 and S2.

Build a Digital Circuit

We will build a circuit called a latch using two transistors. Inputs are the two pushbutton switches and outputs are the two LEDs. Figure 10 is a schematic while Figure 11 shows the wiring. Q1 and Q2 are NPN transistors such as PN2222 or 2N3904. Almost any NPN will do. You can find datasheets on the Internet.