Pressure/Force Sensitive Resister and a door sensor, Works!


I am building an Outdoor rinse shower near my pool. I have a need for a waterproof switch activated by some one standing on a wooden grate. I found “Pressure/Force Sensitive Resistors (PSR)/(FSR)” and bought a couple from Sparkfun:

I thought it would be amazing if I could just wire that into the internal 2 pin connector of an Ecolink Door Sensor. I think everyone knows that besides the magnet operating the sensor, there’s a couple of pins to “remote the action.” Any dry contact (meaning- doesn’t supply electricity - uses the Ecolink’s,) will work. What I didn’t know is if this resistor would.

The PSR has near infinite resistance (>1m ohm) when no pressure is applied and then drops to around 10k ohms depending on pressure/force. It’s not accurate enough to use as a scale, but if the Ecolink would respond to low(ish) resistance on it’s two pins, I’d be in business. Details on how a PSR works is here:

I would put the senor on the underside of the wooden grate inside a tiny waterproof container, such that the active end of the PSR would be “squished” by someone standing on the grate. The Ecolink would in turn energize a power socket that has a 24vac sprinkler transformer plugged in, which energizes the sprinkler valve and starts the water flow.

This image is the initial spark…

I got the package of PSRs today and wired one up to a spare Ecolink Door Sensor (DWZWAVE2-ECO) and pushed on the PSR. The light blinked!! And then when I removed my finger, it blinked again. I could also see on the status pane for the door sensor it would go from open to closed. I tested it a lot of ways and found it would work exactly as I’d envisioned.

As I look at it now, wired, ready for installation, I can see how this actually is a “better” door sensor because I could mount it on the hinge side of the door with the PSR between the door and jamb and have the door close “squish” the PSR. (Under a piece of mylar so that the rubbing/friction of the wood does not abrade the PSR.)

(Mark) #2

Nice. Those Ecolink door sensors are handy. I’ll think of a project and consider using an Arduino, then laziness sets in and I use another Ecolink.

(Eric) #3

This is interesting. Amazon also sells these, not as cheap but shipping is free. I’ll get one to mess around with to start.

(Jordon) #4

Have they arrived yet? I was thinking of ordering a few for myself. Ganna put it under toilet seat so when i sit on it the fan turn on. Haha

(Eric) #5

Mine should be here tomorrow.

(Jordon) #6

Could you let me know how it goes for you. If it works well then imma order some up and see what other projects i can think of.

(Eric) #7

Ok, arriving by 8PM tomorrow. Also, I got mine from Amazon. It’s less expensive when you factor in reasonable shipping.

(Eric) #8

Ok, so it arrived just now (a day late).

Basically, it works. It closes the circuit with a very low amount of pressure. Tapping your finger on it like you were tapping on a table waiting will set it off.

(Jordon) #9

Yay!! So i was wondering. Is the weight it lists a max and could break if more or is it more for programing?


Mine is quite compact and I expect to use a Class 3 Lever to limit the force/pressure. That’s where the sensor is between the fulcrum and the force. Imagine a “stick” where one end is secure and the other floats. The force sensor goes close to the fixed end. When force is applied to the floating end, the max pressure on the sensor is limited by the height of the fixed end.

An example of this is the old time microswitch.

For the lever on the outside, there’s a limit on the force against the nub that works the switch.


I’m still working out the waterproofing of the Ecolink. I’m expecting to either use an existing “foot” or “pad” on the wood grate or add another where it works out mechanically. The idea I’m pursuing is to Dremel out a gap in the rubber foot to insert the FSR. Then, when someone steps on the wood grate, their weight squishes the modified pad and applies pressure to the sensor. The Dremel’d gap is “trial-and-error calibrated” to just barely not touch the FSR, yet contact it with “one 4yr old kid weight.”

Obviously you can do the same with the toilet idea… adhere the FSR to the underside of the seat, adhere a pad on top of the FSR such that it has no pressure, until a human sits, thus squishing the pad and FSR, yet limited by the hard feet already on the seat, and the placement of the FSR close to the hinge end.

(Jordon) #12

Awesome! Thank you so much for your help with this. Deffinetly made things easier for me. I think im going to just go with what you reccomended. It seems simple enough. Great idea you have here. I feel myself wondering around the house wonder what else i can do. Hahaha
On a seperate note i noticed the other senors on amazon for bending. Wonder how those can be used. :thinking:


I’m sorry… I was concentrating so on finding a class 3 lever example, I never noticed that the example I picked, the microswitch, has TWO levers. The outside one, with the roller, is the class 3 that I was trying to show. Inside, however, the actual electrical switch, is a class 2. Fulcrum, then force from the “nub” and out at the “floating end” is the contacts of the switch. Therefore, my example was confusing since I didn’t point out I was referring to the outside one. Both class 2 and 3 levers have the fulcrum at the end like this. Class 1 levers have the fulcrum in the “middle” and the motion of the lever changes direction, like a pry bar laid over a log to lift a rock. You push down on the pry bar and the rock moves up.

I’m going to assume Wikipedia does a better job explaining than me:


I’ve already got WebCore doing the action. When the pressure “button” is pressed, the shower comes on and stays on for 20 seconds after. Over lapping pushes will cause the shower to stay on.

I hope :slight_smile:

(Levi) #15

Inspired by this and my lack of trust with the smartlocks & SmartThings I used a ecolink sensor and the pressure resistor to create a deadbolt sensor. I just really wanted to see the status of my deadbolt since I often lock it but then can’t remember if I did or didn’t lock it.

I ran the wiring behind the trim and added a piece of Velcro on the resistor to protect it from rubbing the deadbolt. So far works pretty well.

Old fashioned manual door lock - but is it locked?