please help

[blindpanda]

I'm a newbie just incase you couldnt tell.. anyway. Okay, so I just bought a moisture detector kit. It runs fine, got it all soldered together, perfect. I took two leads coming from the low moisture LED. I have a 12V pump I want to run off these leads (I do have the 12v battery also), but obviously the LED is something like 2V. So i've been looking around, and I've found ideas, and here I'll go with them. Keep in mind, I'm open to makeshift type setups.

1) A put a CDS right near the low moisture LED. I don't know the details of this, but it would have to be something like 12V resistance closed and no resistance open? This is very makeshift, and I don't even know what CDS I would use, once again I'm a newbie.

2) A relay. I have no clue what they do, I know how they work, but I don't know what the SPDT and RFQX2 or whatever that stuff means. It seems to be the better option, but I'm clueless to it.

3) A solenoid and a push button switch. Sadly enough for me, I can't find a solenoid that is 2V.


Please feel very free to ask me any questions, I need help. I know some electronics, but not alot. I can follow a schematic, so that could be helpfull.

I know this entire post shows my ignorance toward the subject, but low money is forcing me to make this instead of buy.

THANKS A TON!!! in advance.


Products I bought:
https://www.goldmine-elec-products.com/prodinfo.asp?number=G15563
https://www.goldmine-elec-products.com/prodinfo.asp?number=C4744
https://www.goldmine-elec-products.com/prodinfo.asp?number=G15565&variation=&aitem=1&mitem=16

 

[RadioRon]

My favorite approach would be to use the current that would normally have gone through the LED and put that into a transistor switch instead. LEDs are often setup to pass about 20 mA through them (this is determined by the value of the resistor that is probably wired in series with the LED). This current could be used to drive a transistor switch instead. I guess we should sketch a bit of a schematic to show how this hookup would work, but its pretty easy.

 

[blindpanda]

If you don't mind, a quick paint schematic would be great. Thanks a ton for your help. I get what you are saying completely, just want to make sure I do this right.

 

[RadioRon]

Here are some alternatives depending on how the LED is wired in your sensor. If the LED and resistor are connected like shown at A or B then use that schematic to the right of that. Ditto for C or D.

As you will see, this is a simple circuit that suffers from needing a fancy power resistor. It would be better to use a P Channel MOSFET as the pass transistor, but I didn't have the time to work on that. Perhaps someone else could recommend one. Such a thing could avoid the need for a 6 Watt resistor.

 

[Optikon]

I vote for that Q1 to drive the coil of a relay. Less losses & fewer parts.