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I have a coffee machine that has one button. When this button is pressed, the coffee machine will do its thing and automatically shut off after a certain period of time.

I need to use a signal from an Arduino paired with a relay to turn this coffee machine on automatically. I don't have too much experience doing things like this so I need some advice. My instinct is to short out the button in the machine and just turn it on/off with the relay. Would this make sense?

Obviously since coffee machines differ, I'm not asking for the exact process. I would like some advice as to how I would go about doing this on any coffee machine (what to look for, etc). Also, I'd like to know what my other options are.

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I think the answer made by @Ecnerwal makes the most sense. It is much neater than the hobby servo thing hot melt glued in place near the push button. The button is likely a simple momentary close thing so if you wired two small wires, one to each side of the switch you could bring those over to a small jack on the back or side of the coffee maker. Drill a small hole through the plastic housing of the maker and you end up with a coffee maker that looks almost unmodified. Then you can connect to it with an off the shelf cable that was compatible with the jack that (continued) – Michael Karas Mar 7 '14 at 4:16
(continued from above) you had selected. This could be a 1/8" miniature phone jack for example and then you use a low cost audio extension cable over to your Arduino. – Michael Karas Mar 7 '14 at 4:18
@MichaelKaras If it's an electronic K-cup sort of thing, yes. If it's a kettle with a mechanical latching shut-off, maybe not. I would not put a voltage connected to the mains through a 1/8" phone jack unless I was trying to kill someone. – Spehro Pefhany Mar 7 '14 at 4:19
Actually I'd put the small relay inside the Coffee pot enclosure too and then bring the relay coil contacts out the jack. Obviously it all depends upon the type of mechanism and coffee brewer involved. – Michael Karas Mar 7 '14 at 4:25
@MichaelKaras That sounds reasonable. – Spehro Pefhany Mar 7 '14 at 4:43

If you get in far enough to short out the button, you're in far enough to bring the button contacts out as wires, so you can use a much smaller relay to momentarily close them, just as you do when you push the button. That leaves the heavy power handling where it belongs, in the appliance that was designed to do that. Just close the switch for 1/2 second or so and let the coffee machine do its thing.

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oh this makes much more sense. I will look into this. thank you – Byron S Mar 7 '14 at 2:58

If you want to go even further (or maybe not as far) as Ecnerwal suggests, you could use an RC servo to push the button and keep everything you're doing low voltage, and everything that is mains voltage inside the appliance.

enter image description here

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Yup, that works too, and no modifications needed to the coffeepot. Cue George Carlin on the Coffee Freak that flips out when the coffee urn breaks... youtube.com/watch?v=kTuPwkkhtrc – Ecnerwal Mar 7 '14 at 3:16
This would definitely simplify things. Only problem is that I need to build this thing on saturday and I would need to find a local store that sells this due to shipping taking too long. I doubt I can find a store. – Byron S Mar 7 '14 at 3:17
No hobby shops nearby? – Spehro Pefhany Mar 7 '14 at 3:20
@ChrisStratton A valid criticism, also a lot less available. I'll change the photo and link to a bog-standard traditional type which should be more appropriate (and far more available). – Spehro Pefhany Mar 7 '14 at 14:13

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