This circuit uses only passive components but produces a nice sound on a speaker. It can be used in systems of warnings, alarms, calls, etc.
The relay operates on this circuit as a vibrator, although this is not an intended purpose for this type of component.
The sound frequency is determined by the electrical and mechanical characteristics of the relay. We can modify its behavior by connecting a capacitor of 10 to 100 nF between terminals 1 and 2 in the diagram.
The circuit is supplied with 6 or 12 V depending on the relay used. The loudspeaker is of any type 4 or 8 ohms and its purpose and amplify the current variations in the relay, producing sound.
By replacing the pressure switch with a manipulator we can set up an experimental telegraph or even train telegraphy.
In figure 1 we have the diagram of the apparatus and in figure 2 its assembly.
Material list
K1- 6 or 12V relay
S1- Pressure switch NA
FTE- 4 or 8 ohm - small speaker
B1-6 or 12 V- batteries, battery or power supply
Miscellaneous: wires, solder, battery holder or power supply.
