9V input. Output range: 5V-6V over twelve "keys." Designed to be connected to twelve simple switches or buttons and fed into an oscillator's CV input jack.
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Note: This design also features a space (currently unused) for a built-in dual oscillator (SN74LVC2...
Water detector with 4 level stages. Each stage makes the 555 timer to give a supply period for the buzzer. The active buzzer transmits sound with a pause period between 0.5-3 seconds, depending on the level detected.