Help needed for pressure switch/sensor/plate

Thread Starter

TechGirl

Joined May 23, 2019
10
Hello folks,

I'm fairly new to electronics but the more I read and the more I tinker the more I learn. I would like to build a simple battery operated circuit that uses a pressure switch/sensor/plate but I can't seem to find such a switch when searching sites like this or just general google searches so maybe I'm not searching on the right keywords.

I want it to be small like a regular push button switch and the behavior is that the circuit stays closed while there is pressure and open when there is no pressure. An example would be holding your finger on the switch keeps the light on. The minute you take your finger off the light goes off.

I've seen pressure plates but they are way too big. I wouldn't mind something like that but scaled way down. Just a tiny pad/plate is needed.

Thanks in advance for any help provided!


Karen
 

Yaakov

Joined Jan 27, 2019
1,611
Welcome to AAC.

What you are looking for is generally called a “touch switch” and it is not usually pressure sensitive, but capacitive. It uses the current capacitively coupled in the sensor input to trigger the circuit, like a touch screen.

Look at these: https://www.ebay.com/bhp/touch-sensor

Most provide logic level (3.3V or 5V) output, and wouldn’t be doing the switching directly, you’d have other circuitry to act on the signal as you’d like.

If you really need a pressure sensor, that’s something different. Could you be more specific about the application, it will make it easier to help. The more clearly you explain how you will actually use this, the better our answers.
 

Thread Starter

TechGirl

Joined May 23, 2019
10
... try a search for 'momentary switch'.
Thanks for the speedy reply!

Two questions about these:
1. I'm assuming these types of switches can be kept on for an indefinite amount of time without destroying them?
2. This is pretty close to what I need in so far as behavior goes but I need something flatter. The idea is that the circuit is activated when something is placed on it and presses down on the switch and the circuit is de-activated when the item is removed. Think of a mug being put down on a coaster. The switch would be in the coaster.

Any thoughts? I tried searching "flat momentary switch" but the only thing that comes up are push button switches.

Thanks again!


Karen
 

Thread Starter

TechGirl

Joined May 23, 2019
10
Welcome to AAC.

What you are looking for is generally called a “touch switch” and it is not usually pressure sensitive, but capacitive. It uses the current capacitively coupled in the sensor input to trigger the circuit, like a touch screen.

Look at these: https://www.ebay.com/bhp/touch-sensor

Most provide logic level (3.3V or 5V) output, and wouldn’t be doing the switching directly, you’d have other circuitry to act on the signal as you’d like.

If you really need a pressure sensor, that’s something different. Could you be more specific about the application, it will make it easier to help. The more clearly you explain how you will actually use this, the better our answers.
Thanks for the welcome!! I posted a reply to the momentary switch response that gives a bit more detail. I guess what I'm looking for is more like a pressure plate in so far as it being flat and it activates when pressure is detected. For example... think of a mug of coffee on a coaster. The switch would be in the coaster. I guess it doesn't necessarily have to be pressure activated it just seemed to make sense to be a pressure type switch. When the mug is on the coaster it pushes down on the switch and the switch turns on and warms up the coaster. Take the mug off and the switch turns off. As mentioned a pressure switch seemed to makes sense in this regard because it's automatic in its behavior. I don't think any of the other switch types are meant to be kept in the on position (closed circuit position). Like a push button is meant to be pushed and released. Not held pushed down. :)
 

Yaakov

Joined Jan 27, 2019
1,611
Thanks for the speedy reply!

Two questions about these:
1. I'm assuming these types of switches can be kept on for an indefinite amount of time without destroying them?
2. This is pretty close to what I need in so far as behavior goes but I need something flatter. The idea is that the circuit is activated when something is placed on it and presses down on the switch and the circuit is de-activated when the item is removed. Think of a mug being put down on a coaster. The switch would be in the coaster.

Any thoughts? I tried searching "flat momentary switch" but the only thing that comes up are push button switches.

Thanks again!


Karen
Happy to help.

I will point out that you mentioned a finger in your first question, which is not the same as a mug! Those switches will work with the former but not the latter. So, is it a mug, or something else?

If it is going to be an object and not a body part, I would suggest that fabricating what you need from a microswitch and a platform is the first thing I would think of.

Something like these: https://www.ebay.com/itm/50x-Ultra-Small-Lever-Actuator-Microswitch-SPDT-Miniature-Micro-Switch-2A-125V/173698966843

Now, if the entire thing must be very flat (no base, etc.) you will have to work something else out, so... in order to answer properly, could you explain the whole project?
 

Thread Starter

TechGirl

Joined May 23, 2019
10
Happy to help.

I will point out that you mentioned a finger in your first question, which is not the same as a mug! Those switches will work with the former but not the latter. So, is it a mug, or something else?

If it is going to be an object and not a body part, I would suggest that fabricating what you need from a microswitch and a platform is the first thing I would think of.

Something like these: https://www.ebay.com/itm/50x-Ultra-Small-Lever-Actuator-Microswitch-SPDT-Miniature-Micro-Switch-2A-125V/173698966843

Now, if the entire thing must be very flat (no base, etc.) you will have to work something else out, so... in order to answer properly, could you explain the whole project?
Thanks for this! Why would a finger pushing down and putting pressure on a "switch" be different than a mug putting pressure on it? Isn't pressure the same in this case? I haven't thought out the entire project because I haven't been able to find a switch or sensor or pad that does what I want. LOL It might be something that warms up when you put a mug on it or maybe it lights up when you push down on it or maybe it will play a song. Whatever the project is I envision it as a base of some sort and when you touch it (press down on it) or put something on it then it will do something. :)
 

djsfantasi

Joined Apr 11, 2010
5,848
Thanks for this! Why would a finger pushing down and putting pressure on a "switch" be different than a mug putting pressure on it? Isn't pressure the same in this case? I haven't thought out the entire project because I haven't been able to find a switch or sensor or pad that does what I want. LOL It might be something that warms up when you put a mug on it or maybe it lights up when you push down on it or maybe it will play a song. Whatever the project is I envision it as a base of some sort and when you touch it (press down on it) or put something on it then it will do something. :)
A mug may not press hard enough to depress a push button. That would be the difference.

Search for microswitches. Some even come with a lever attached to increase the force and area so as to activate the switch.

Here’s another suggestion. Microswitches are used as sensors, such as when a door is closed or as limit switches.

Here’s an article on microswitches.
 

SamR

Joined Mar 19, 2019
1,509
I've seen pressure plates but they are way too big
The microswicth is what is typically used. And it is big. Look at membrane switches. Such as those used on numeric keypads. They are not typically used for what you are asking, but you might find some ideas. To wit: "In a non-tactile switch, there isn’t a physical snap or indicator that the button has been pressed. It’s usually indicated through lights, sound or reading on the instrument display. On a non-tactile switch, the bottom side of the overlay is connected to a conductive pad or an upper circuit layer is printed with conductive traces. When the overlay is pressed down the conductive traces connect to the lower circuit layer which sends a signal to a printed circuit board."

So it is normally open and you would need to invert the signal to make it normally closed.

Good Luck and Welcome!
 

Thread Starter

TechGirl

Joined May 23, 2019
10
Thanks everyone for your great suggestions!! All of these have given me ideas. I like the touch sensors. It's not what I was thinking of for my pressure switch project but it has given me an idea for something else.

Thanks also SamR. I can visual what you mean regarding the overlay pressing down on the conductive layer to activate the circuit. Ironically when I was googling for pressure switches I came across a guy who made a pressure plate out of a few pieces of cardboard, wire and tin foil. The cardboard was wrapped in tin foil and the wires hooked up such that when the two pieces came together the circuit became active. He made it for a haunted house. The idea being when someone stepped on the "plate" it lit up something on the other side of the room and of course when they stepped off it the connection was broken. He hid it under a carpet. LOL!! This idea has probably come the closest to my idea of something pressure activated.

I have a lot to look up and read about. If I get my project going I will post it here. :)

Cheers.


Karen
 

Yaakov

Joined Jan 27, 2019
1,611
Gettin back to this a bit late but to clarify, the capacitive touch switch will work with a finger because it will capacitively couple energy into the circuit but not with the much.

The thickness of the device is very important as well since some approaches require more depth.

Fabricating your own pressure switch will be fun and interesting but it is unlikely to have a long operating life.

Good luck and have fun.
 
Last edited:

Alec_t

Joined Sep 17, 2013
10,614
Years ago I made an under-carpet pressure plate using a matrix of paper-fasteners inserted into a base-plate of hardboard, overlaid by a thin sheet of plastic foam with holes to match the fastener positions and topped off by a thin sheet of aluminium. Pressure on the carpet brought the top sheet into contact with the heads of some of the fasteners to complete a bell circuit.
 

djsfantasi

Joined Apr 11, 2010
5,848
@TechGirl

Several people have made good suggestions. Push buttons, microswitches, membrane switches, pressure pads, even DIY versions of the above.

But it’s important to note that it depends greatly on what you are sensing. You mentioned that it might be a mug... Well, the pressure exerted by a mug is not going to be detected by a DIY pressure pad, such as the one Alec_t described. They are going to need the weight of a person to trigger.

And besides, you mentioned that this was going to be a base project. You hinted that you might want to use it in different situations. Different situations may require different solutions.

If you pick one specific applications, we can select an appropriate solution.
 
Last edited:

Yaakov

Joined Jan 27, 2019
1,611
@TechGirl


Well, the pressure exerted by a mug is not going to be detected by a DIY pressure pad, such as the ones Yaakov and Alec_t described. They are going to need the weight of a person to trigger.

If you pick one specific applications, we can select an appropriate solution.
Just to clarify, I didn't suggest or describe a homebrew pressure pad. My suggestion was a microswitch and a platform which could be easily calibrated to handle a mug, or less, or much more.

As far as picking a lane, I agree. What appears to the TS to be a class of problems is not one in the domain of solutions. There are several classes of problem here.
 

SamR

Joined Mar 19, 2019
1,509
The real drawback to membrane switches is that they are not an off-the-shelf solution as most are custom made for a particular application. At one time they were used as automatic door openers and were soon replaced by much better devices the ultrasonic or infrared detectors.
 
In addition to what has already been offered, I would add:

Force sensing resistor. https://www.interlinkelectronics.com/standard-products

These come in many sizes and shapes and are very thin (and can be covered). Typically, you use an op amp in a comparator configuration to functions as a threshold switch.

You can even use conductive foam (the stuff that ICs sometimes come packed with) to make a pressure switch - https://alemontanari.wordpress.com/2014/02/25/diy-pressure-sensor-with-conductive-foam/

On the capacitive touch switches...cheap ones, like these https://usa.banggood.com/TTP223B-Digital-Touch-Sensor-Capacitive-Touch-Switch-Module-For-Arduino-p-1158322.html?rmmds=search&cur_warehouse=CN will NOT hold the "touch" output indefinitely (they also may not latch as you would expect). I have some and it was very frustrating to realize that.

Finally, remember that with any kind of touch switch you have to consider safety to avoid receiving an electric shock.
 
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Thread Starter

TechGirl

Joined May 23, 2019
10
Thank you @Raymond Genovese. The force sensing resistor might be what I need.

Thanks to all for providing me with great options all of which can be used for various types of projects.

@djsfantasi and @Yaakov. I originally hoped there might be one type of switch, pad, resistor, etc that I could use that could be calibrated for various uses (ex: putting something heavy on it like a mug or pushing down on it with your finger) but based on the answers I have received there might not be one magic component that will work for different pressures/weights, etc. being put upon it.

I guess at a high level I was thinking of a decorative base (possibly made out of laminate) and when you put something on it (like a mug) then the base would do something (ex: light up) and when you take the mug off it shuts off. I would somehow have to secure the component so it can receive the pressure needed to activate it but be safe so it can't give off a shock.

What's interesting is that after reading the answers people have provided I just realized I have a microswitch in my collection of components. I had no idea what it was or what it did until this post. LOL!! It was sold to me as a possible alternative to a liquid float switch but I don't think I can safely make it work for that however it might work for this project.

:-D
 
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