PCB Step 3: Make Some Noise

Goal#

Finish the timer circuit, add the amp circuit, and test the speaker.

Components#

  • Timer circuit
    • 100k resistor * 1
    • 100 resistor * 1
    • 10k resistor * 1
    • .1uF ceramic capacitor * 1
    • 4.7uF electrolytic capacitor * 1
    • 10nF ceramic capacitor * 1
    • 1k trimmer potentiometer * 1
    • IC socket * 1
    • 555 timer chip * 1
  • Amp circuit
    • .1uF ceramic capacitor * 1
    • 47nF ceramic capacitor * 1
    • 10 resistor * 1
    • IC socket * 1
    • 220uF electrolytic capacitor * 1
    • 1k trimmer potentiometer * 1
    • 100 resistor * 1
    • speaker * 1
    • 386 amp chip * 1

Steps#

  1. Finish that first timer circuit
    1. Solder the 100k resistor to R2.
    2. Solder a 100 resistor to R3.
    3. Solder the 10k resistor to R4.
    4. Solder a .1uF ceramic capacitor to C1.
    5. Solder the 4.7uF electrolytic capacitor to C2.
    6. Solder the 10nF ceramic capacitor to C3.
    7. Solder a 1k trimmer potentiometer into RV1.
    8. Solder an IC socket into U1.
      • The legs of the socket may be bent from shipping. Make sure they're all straight and intact when inserting into PCB and before soldering. De-soldering a damaged socket is no fun! Do this for all the IC sockets for the rest of the assembly process.
  2. Solder the amp circuit
    1. Solder a .1uF ceramic capacitor to C62.
    2. Solder the 47nF ceramic capacitor to C63.
    3. Solder 10 resistor to R83.
    4. Solder an IC socket into U22.
    5. Solder the 220uF electrolytic capacitor to C64
    6. Solder a 1k trimmer potentiometer into RV21.
    7. Solder a 100 resistor to R82.
    8. Solder the speaker.
      1. Strip about 1/8" of the insulation off wire's ends.
      2. If necessary, solder wires to speaker. The lighter wire goes to + and the darker wire goes to -.
      3. Just like you did for the battery snap, feed wires through the relief hole above SPK, then solder them into place: lighter wire to + and darker to -.
  3. Insert IC chips
    1. Insert the 555 timer chip into its socket at U1, making sure it's in the right orientation: a notch or dimple at the top of the chip should match the notch in the footprint outline on the PCB.
    2. Insert the 386 amp chip into its socket at U22, again making sure its in the right orientation. You'll do this for all chips throughout assembly.

It should look something like this when done#

It should look something like this when done

remember

The components' brands and colors for PCB, LEDs, and wires may look different from yours, and that's okay! What's important is that the part types and values are in the right spots.

Test it#

  1. With the battery attached, turn the power switch on. You should hear a little "boomp" noise from the speaker as it's powered by the amp.
  2. Press S1 again. In addition to the LED being lit, you should now hear an audible tone out of the speaker!
  3. Try adjusting the pot at RV1. Turning it clockwise should make the frequency go up, and vice-versa.
  4. Try the same on the volume pot at RV21. Clockwise should make the sound quieter, and counter-clockwise will be louder.

Troubleshooting#