Here's a universal 555 frequency generator with four frequency ranges that might be handy for building any projects that deal with frequencies. JP3 is a button used to switch the device on and off. The power supply (anything from 4-12V) is connected onto JP4. JP2 serves as the output for the signal with an attenuator, if we don't need the full strength (voltage) of the signal, only, say 3V of 5V. We can set the output value by R2. JP1 gives the full strength of the signal, with a current depending on the 555 type you use. R3 is used to set the frequency within a range chosen by the DIP switch S1. You can set which range of frequencies you want to use with a DIP switch. With it you enable or disable a capacitor which is hooked up into the datasheet circuit of the 555 chip.

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