Good Morning!
I have built a 12V battery powered solar circuit to water our garden while we are away on vacation. It consists of a 555 set up as a one shot, triggered by a 2n7000 mosfet. It will hold open a solenoid valve long enough to fill a 5 gallon pail from a storage tank. The pail then gravity drains into drip tubes.
I can trigger it with switch contacts easy enough, and it works well. Here's the rub... I don't want a digital arduino type set-up. And I cannot use an op-amp because of the need to pull down to the ground rail from a single supply. The mosfet would never turn off. I cannot use a bjt transistor because of the analog solar voltage. No sharp turn on.
I cannot use a relay because of the variable solar panel voltage output being too high for a 5-10 volt coil, and a 12volt coil would retrigger when clouds go by.
The only two solutions I can come up with is a 7805 voltage regulator powering the relay coil, or use a 556 dual timer to use the second timer as a comparator and it would sink current when low, shutting off the mosfet.
Does anybody have any better ideas?
Thanks
Mike
I have built a 12V battery powered solar circuit to water our garden while we are away on vacation. It consists of a 555 set up as a one shot, triggered by a 2n7000 mosfet. It will hold open a solenoid valve long enough to fill a 5 gallon pail from a storage tank. The pail then gravity drains into drip tubes.
I can trigger it with switch contacts easy enough, and it works well. Here's the rub... I don't want a digital arduino type set-up. And I cannot use an op-amp because of the need to pull down to the ground rail from a single supply. The mosfet would never turn off. I cannot use a bjt transistor because of the analog solar voltage. No sharp turn on.
I cannot use a relay because of the variable solar panel voltage output being too high for a 5-10 volt coil, and a 12volt coil would retrigger when clouds go by.
The only two solutions I can come up with is a 7805 voltage regulator powering the relay coil, or use a 556 dual timer to use the second timer as a comparator and it would sink current when low, shutting off the mosfet.
Does anybody have any better ideas?
Thanks
Mike
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