Price - Stock No 242 

Listen to audio for the Three Tone Door Bell 




1. Check your P.C.Board carefully for damage to the tracks. A Circuit Tester or a multimeter will help check that there are no broken tracks.

2. Identify the resistors by their colour bands or with a multimeter. Bend the legs with long-nose pliers to match their holes and push them into place against the surface of the board. Remember that the drawing is looking at the PLAIN side with the tracks away from you. When in place, bend the legs sideways a bit to stop the resistors from falling out.   Solder in place - see Soldering Technique

3. Use care when inserting the IC socket.  Solder in place.

4. Identify the PCB pin locations, insert and solder.

5. The BC 548 must be inserted in the correct orientation.  It
  has a flat on the body.  Mount it with the flat as the drawings show.  Care should be taken when soldering the transistors - excessive use of heat from the soldering iron may permanantly damage these components (a heatsink tool or long nose pliers will dissipate excessive heat). 

6. Solder the positive and negative leads of the battery holder to their respective pins.

7. Cut the fig. 8  wire into two appropriate lengths, one for the speaker, one for the switch.  Strip the insulation approx 5 mm from each end.  Tin the ends of the wire - See Tinning wire .

8.  The Speaker has +ve and -ve terminals, use one length of fig 8 wire to connect the terminals to their respective PCB pins.

9.  Use the second length of fig 8 wire to connect the switch to the chosen trigger.

10.  You will find that the legs of the HK522 are spread a little wide to fit into their sockets.  Take each IC and rest  the  legs  on  a flat  surface.   Gently  push  down  so that row of legs is straightened a little.  Repeat for the other row of legs.  Take the IC and find the locating mark on the top surface and near or at one end.  Check the drawing and push it into its socket the right way round. 

11. Insert batteries and press the switch to test.

Trouble shooting

Troubleshooting  if necessary will involve careful checking of locations and polarity of components. Re-solder all joints and check to make  sure  you  have  not  bridged across  between  any  two adjacent component legs.  The end  of  a  broken  hacksaw  blade  sharpened  on  an  emery wheel is a good tool for cleaning between soldered joints.

Technology Notes

The heart of this kit is the HK522 which is a purpose built Integrated Circuit for melody generation.  The output of this IC is fed to the Base of the BC548 via the 1K resistor.  The BC548 amplifies the sound for output by the speaker.  See - Transistors

View the HK522 Datasheet

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