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I have a water detection circuit that uses 3/4's of a 4066 (SW1-3) as a 3-level sensor and the 4th to power the coil of a 12v relay which will provide power to a water pump if the water level is at least at the minimum level. The sensor works and powers 3 LED's to visually indicate water level. However, the switch to the relay powers the coil which then stays on even after the sensor is unshorted. And, while the coil is attached, the current apparently bleeds over to SW2 so that the LED attached to that switch also comes on. The connection to the relay coil is: GND > Pin 11, Pin 10 > relay coil, relay coil > +12V. Pin 12 is the trigger for the switch. My guess is that I need to do something to bleed off the coil when there is no current applied but I have no idea what needs to be done there. Any suggestions would be greatfully appreciated. Thanks

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  • \$\begingroup\$ What current is used to drive the relay? And did you check the 4066 datasheet for maximum (current) ratings? \$\endgroup\$ – jippie Nov 25 '12 at 8:20
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I think you are pushing the 4066 far beyond its limits by powering a relay coil from it. The chip heats up to a point that the other switches fail too ("current apparently bleeds over to SW2"). If the chip still functions after you manually 'reset' it by removing power to it, I think you are just plain lucky.

The solution will be that you power your relay with a separate transistor (and flyback diode). A bit like this answer

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