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DRINK_AID_FOR_THE_BLIND

2014-11-05 07:31  
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DRINK_AID_FOR_THE_BLIND
The circuit is an audio oscillator based around IC1, a 555 astable that drives a piezo disk directly. Transistor TRI acts as a switch and will enable the audio oscillator when the two probes detect liquid. By using two sets of probes formed at different lengths (see inset diagram), the audio alarm will activate when enough milk, then enough water, has been added. The circuit is powered by a small 12-V battery (e.g., MN21 type), which should give many years of continuous service because the quiescent current is virtually nil. The device was housed in a small circular plastic box, approximately 4 cm in diameter. The probes were formed from sheathed, thick solid-core copper wires protruding from either side so that the container could clip onto the side of the cup.