Now it’s time to
mount the components on
both sides of the PCB. The
LED PCB is shown in
Figure 31. The side with
the text “ImagesCo.” is the
top side of the board.
Mount and solder the
components as described
next. Depending on which
color cube you select, the
resistors R1, R2-R4, and
R5-R16 will have different
values. For the RED cube,
the value is 220 ohms. For the YELLOW and GREEN cubes, the value is
180 ohms. For the BLUE cube, the value is 150 ohms.
On the top side of the PCB:
1. Mount resistors R1 (150/180/220 ohms), R5–R16 (150/180/220
ohms), R21–24 ( 4.7K ohms), and D1 (tin wire jumper in its place) on the
top side (see Figure 32).
2. Mount resistors R2–R4 (150/180/220 ohms).
On the bottom side of the PCB:
3. Mount and solder R17–R20 (220 ohms) and crystal X1 ( 16 MHz).
4. Place the DIP 40-pin socket on the bottom side.
5. Place the capacitors C3 and C4 ( 22 pf).
6. Place capacitor C5 (0.1 µF).
7. Mount transistors Q1–Q4 ( BC 369) on the bottom side. The
flat side of the transistor faces in toward the PCB. The curve/arc of
the TO-92 transistor package faces outward from the PCB. Figure 33
shows a close-up of the transistors.
8. Mount the tactile switches S2–S5 onto the bottom side.
9. Mount the slide SPDT switch S1 onto the bottom side. The
footprint is smaller than the switch lead pitch, so you will have to
bend the outer leads slightly inwards using needlenose pliers.
10. Mount electrolytic capacitor C2 ( 47 µF/50V).
11. Mount electrolytic capacitor C1 (1,000 µF/16V).
12. Mount regulator U1 (7805) onto the bottom side. Bend the
regulator inwards from the bottom side completely so that it touches
the PCB. Cut the extra (unwanted) leads from the top side, and then
solder the leads from the top side.
13. The 10-pin header P2 is optional and doesn’t have to be
mounted. The DC barrel jack P1 should be soldered after the LED
matrix is mounted on the top side.
14. Insert the programmed PIC16F877A into the 40-pin DIP
socket with the correct
polarity on the bottom
side of the PCB. You can
use a pin straightener for
easier insertion into the IC socket (see Figure 34).
15. Mount the four L brackets on the bottom side of the PCB with four
small snap rivets. With the correct orientation, align the hole on the small arm
of the L bracket to that of the mounting hole on the bottom side of the PCB.
Place the small pop rivet from the top side into the mounting hole and press it
until the rivet head touches the PCB. This will secure the L bracket into its
place (see Figure 35).
Figure 31. Top view PCB.
Figure 32. Top view PCB (populated
Figure 33. Bottom view PCB; close-up shows
the transistor orientation.
Figure 34. Bottom view PCB, populated.
Figure 35. Close-up of the L bracket, held with a plastic push rivet.