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                                                      Bots / The Ultimate Palm Robot/ Mukhar & Johnson / 222880-6 / Chapter 9






                    248     The Ultimate Palm Robot



                    LEDs

                               The first output project we will look at is an extremely simple one. Light
                               Emitting Diodes, or LEDs, can be directly attached to either the SV203 or the
                               BrainStem. (Now these are not exactly the same as death ray lasers, but if you
                               squint your eyes a little, you can pretend they are almost the same.)

                                 We started by connecting an LED to the analog output ports of the SV203
                               and the BrainStem controller. Later in this chapter, in the section “Using Digital
                               Components with the BrainStem,” we’ll connect the LEDs to the digital output
                               ports of the BrainStem.
                                 We used simple colored LEDs available from various sources. The ones we
                               used are from Radio Shack, part numbers 276-022 and 276-041.
                                 LEDs have two leads—one known as the anode and one known as the cathode.
                               If you look at the LEDs, you’ll see that one lead is shorter than the other. The
                               shorterleadisthecathodeandthelongerleadistheanode.Theanodeisattached
                               to the signal, or Vo, line. On both the SV203 and the BrainStem, this is the pin
                               farthest from the edge of the board. The cathode is attached to the GND line of
                               the controller. For both the SV203 and BrainStem, this is the pin closest to the
                               edge of the board.







                                                                                     Anode
                                                                                     Cathode






                                  Using the programming we saw in Chapter 7 and Chapter 8, we can drive
                               the LEDs so that they light up on command. With the SV203, we will use the
                               SVn Mn command. Recall that the SVn command is used to select an output
                               port; the Mn command sets the output port to a particular value from 0 to 255.
                               The value 255 will cause the LED to light. For example, this line of BASIC code
                               will cause an LED connected to output port 4 to light:


                               print #5, "SV4M255"










           P:\010Comp\Bots\880-6\ch09.vp
           Monday, May 12, 2003 4:33:45 PM
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