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This question already has an answer here:

I have an espresso machine that I tore down, reassembled with fewer components then modified it to fit a specific setup -- kind of DIY project.

The machine has an autofill circuit. After I removed the controller and SSR, the machine does not have an autofill circuit, which is fine when I turn on the pump to refill manually. The only problem is checking the water level to find out when I need to refill the boiler. I fitted a sight glass for that purpose, but I still need another aid to notify me whether the water level is OK or not, mainly in case someone else is using it.

I want to add a small buzzer/LED which is activated only when the water level drops below a certain point, OR just a LED which lights up so long as the water level is fine.

There is a water level probe. The boiler is grounded so if there is water touching it there will be a circuit/current through the probe, and if water is below the tip then there is no circuit (this is my understanding, so please correct me if it is not correct.)

There are buzzer/LED gadgets that can be bought cheap, but I want to know how it would work with the water level probe? I tried connecting the probe to a LED then to one of electric current poles; I thought it should light up when there is water touching the probe, but it does not seem to work, or maybe it is just the wrong way to do it. :)

Any help is appreciated.

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marked as duplicate by Trevor_G, brhans, Community Jan 24 '18 at 3:01

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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    \$\begingroup\$ Let me summarize what I think I read: You re-assembled a machine, with some parts left over. (I've been there!) You appear to have lots of good mechanical knowledge (because of your changes) but not so much electronic (because you just removed the controller and SSR, choosing instead to move towards an almost entirely mechanical means to get the same/similar desired result.) So you are now trying to approach what remains to you with the simplest electronics possible, so to keep it in your range of skillsets? Is that about it? (I'm not complaining. Just trying to make sure I have it right.) \$\endgroup\$ – jonk Jan 23 '18 at 19:37
  • \$\begingroup\$ Why does this sound like an accident waiting to happen..... and one your insurance company will walk away from.... \$\endgroup\$ – Trevor_G Jan 23 '18 at 19:56
  • \$\begingroup\$ I strongly suggest you make that sensor remove the power to the boiler.... \$\endgroup\$ – Trevor_G Jan 23 '18 at 20:05
  • \$\begingroup\$ If you want water to conduct well enough to light an LED, it had better be salty - at least as salty as seawater. If that isn't how you like your coffee, you will need another approach - perhaps a very sensitive amplifier between probe and LED. Hence the transistor in the linked Q&A. \$\endgroup\$ – Brian Drummond Jan 23 '18 at 20:07
  • \$\begingroup\$ @jonk, YES! if a complicated solution is necessary, then let it be:) \$\endgroup\$ – user1824971 Jan 23 '18 at 20:20

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