ironbishop
Posts: 3
Joined: Fri Jul 05, 2019 7:10 am

which sensor to use for a coffee maker

Fri Jul 05, 2019 7:27 am

hi all,
first post here. I wish to add a sensor to a coffee machine, in order to know when I forgot to empty it. Which is the best sensor for this case? I attached a couple of pictures of the inside of the machine.
Attachments
coffee_maker_rest_position.jpg
Machine is empty. Yellow thing is not touching the left thing.
coffee_maker_rest_position.jpg (107.11 KiB) Viewed 453 times
coffee_maker_closed_position.jpg
Machine is full, making coffee. The yellow thing is touching the left thing.
coffee_maker_closed_position.jpg (214.12 KiB) Viewed 453 times

pcmanbob
Posts: 7140
Joined: Fri May 31, 2013 9:28 pm
Location: Mansfield UK

Re: which sensor to use for a coffee maker

Fri Jul 05, 2019 10:39 am

Hi.

I guess you might be able to do it with a micro switch , there are some very small ones out there , but as we have no reference to the size of the parts or space in your picture can't say for sure, as you will need to add a mounting bracket to hold the switch in place.
Last edited by pcmanbob on Fri Jul 05, 2019 10:54 am, edited 1 time in total.
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Andyroo

Re: which sensor to use for a coffee maker

Fri Jul 05, 2019 10:52 am

An other thought is if the machine has a warning light that come one could you either pick up a signal from that or use a light sensor to see the warning light?

ironbishop
Posts: 3
Joined: Fri Jul 05, 2019 7:10 am

Re: which sensor to use for a coffee maker

Fri Jul 05, 2019 11:33 am

There are no lights indicating what I'm trying to monitor. Just an "on/off" one, but it's OK to leave the machine always on.

There is less than a centimeter from the yellow thing to the left thing, in the rest position.

pcmanbob
Posts: 7140
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Location: Mansfield UK

Re: which sensor to use for a coffee maker

Fri Jul 05, 2019 1:09 pm

Well these are some of the smallest micro switches that are readily available

Image

and they are 20x16x5 mm

So I think you are going to struggle to find a switch and mounting to fit in the space you have available.

unless you can mount them in such a way you, that can use a long operating arm to activate the switch.
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ironbishop
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Re: which sensor to use for a coffee maker

Fri Jul 05, 2019 1:40 pm

ok so while I look for a position... what exactly do I need? a (micro) switch? a button? a rele?

pcmanbob
Posts: 7140
Joined: Fri May 31, 2013 9:28 pm
Location: Mansfield UK

Re: which sensor to use for a coffee maker

Fri Jul 05, 2019 1:43 pm

ironbishop wrote:
Fri Jul 05, 2019 1:40 pm
ok so while I look for a position... what exactly do I need? a (micro) switch? a button? a rele?
What you need is a micro switch of the size/type I have shown , you can then connect it to the pi gpio like any other switch.

Edit.. so looking around I did find some ultra mini micro switches at 22.7 x 9.5 x 3.2mm ( body size ) on Ebay.
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JohnsUPS
Posts: 125
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Location: USA

Re: which sensor to use for a coffee maker

Sun Jul 07, 2019 3:00 am

It appears as though an appropriately small micro switch fastened to the "wall" shown on the left side of the picture may do it. The metal actuation arm of the micro switch could be bent to correctly contact the vertical brass (?) cylinder towards the top to maximize the throw of the contacting arm. You could also consider an optical interrupter, but this may be subject to problems if it gets clogged with coffee grounds.

Fastening the switch in place may prove to be the most challenging part. It isn't easy to see how much room you have to work with. Looks like there is already a hole in the plate on the left side, and it might be able to be used to affix a bracket of some sort.

You don't want a relay - wrong item for this application. Also, button switches usually have a very short throw with may limit the movement of the vertical brass cylinder piece and maybe cause unwanted operation unless very carefully mounted. Also, the force of the movement of the brass arm needs to be considered. Seems like a micro switch (like those that were previously pictured) is the best route. Some micro switches have a very light contact force requirement.

Also, make sure that the switch is a sealed type, and will be able to handle any temperature that this cavity may have.

blimpyway
Posts: 185
Joined: Mon Mar 19, 2018 1:18 pm

Re: which sensor to use for a coffee maker

Sun Jul 07, 2019 6:33 am

Assuming the grounds are wet, a simple resistive sensor (as used to test soil humidity) could work. An electrode on the bottom, one closer to the top would drop in resistance when the bin is full.

No moving parts, should consider corrosion - use stainless electrodes, alternating low current

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