Electronic Project
555 Two-Tone Alarm

2-tone diagram

This project is designed to support the Hila demonstration speaker project.

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2-tone step1

With the 555 IC mounted find pin 1 and then connect a wire from pin 2 to pin 6.
Notice the black mark I added to indicate the row that pin 1 is located in.


Connect a 1k (brown-black-red) resistor from pin 2 to pin 7.


Connect a 1 uF capacitor from pin 1 to pin 2.
Note that the "-" side of the capacitor connects to pin 1.


Connect a wire from pin 4 to pin 8.


Connect a 100 uF capacitor from pin 3 to an unused row.
Note the "+" lead of the capacitor is connected to pin 3.


Construct a 7 cm X 18 cm base out of soft wood (pine is fine).
Tack tow thin strips of aluminum to the base.
One strip along the bottom , the other 7 cm from the bottom.
Aluminum can be cut from disposable cookie sheets.
Note the two wires that are ready to be attached.


Complete tacking the two strips in place.
Note the two wires are captured by the tacks.

Two "keys" are in place. The keys are made of aluminum 1.5 cm X 3 cm.
Two resistors, 470 Ohm and 1000 Ohm, are laid in place.


Complete tacking the keys and resistors in place.
Note the resistors are captured by the tacks.
Bend the "keys" up slightly so they don't touch the bottom metal strip.


Use double sided tape to secure the circuit board in place.
Note orientation and location.


Close up showing short wire from aluminum connected to pin 8 and longer wire connected to pin 7.
Red mark indicates row that pin 8 is located in.


Use double-sided tape to secure battery to base as shown.
Black lead (-) from battery connects to pin 1.
Red lead (+) from battery connects to pin 8.


The two wires from the demonstration speaker connect to pin 1 and to the unused row
with the 100 uF capacitor "-" connection.
Look at the image above to clarify connection.


The complete unit.  Pressing the keys produces a tone on the speaker.
The tone is quiet. put your head close to the speaker.
Holding 1 key while pressing the other off and on will create a two-tone alarm sound.

Any speaker will work with this project.


Moving the red (+) wire to an unused row shuts the power off and saves the battery.
Make sure you have plugged into an unused row!  You could damage your circuit.


To turn your circuit on, move the red (+) wire back to pin 8.