Thank you Tom, I really appreciate the help (and this awesome project).
Edit (19/10); I finished this project earlier today - all seems to be working as intended. Such a great project and I’m super grateful to this community and Tom for stuff like this. Though, I feel ESP could be a slippery slope!!
Hi, just got a new mattress
I’m getting Rin= 0.9-1 MOhm when I’m on the bed but I’m not getting any values off the bed Rout
The multimeter only goes up to 200MOhm.
Anyway I could verify the Rout?
Btw, has anyone tried combining 2 units 600mm fsr strip into 1? I’d like for it to detect if I’m sitting on the edge. Not getting any reading with 1 600mm FSR positioned in the center of the bed
I’m using this resistor, and am having a great deal of trouble finding an English datasheet for it. It’s not yet installed, though; I’ve just been testing it under my bed with my multimeter and no other resistors in order to get a sense of the resistor values needed as described in this post.
What is the maximum value your multimeter can read in ohm?
And how is it connected? Crocodile clips may not be the best option.
What were your min and max readings, or is that what you’re saying is fluctuating wildly?
That other post is a great place to ask those questions. I’ve seen a variety of posts about that sensor over there, so you may find some good info. This thread is focussed on a particular product, so it’s less relevant here. Thanks!
That’s totally fair, Stephen, apologies.
I’ve moved these posts over here to keep Stephen’s topic about his (excellent) sensor.
For anyone daunted by the DIY required for this sensor please check out Stephen’s pre-built sensor, highly recommended: Bed Presence for ESPHome by Elevated Sensors
My multimeter is listed as having a range of “999.9Ω/9.999kΩ/99.99kΩ/999.9kΩ/9.999MΩ/99.99MΩ±(2%reading+10)”, and it’s in an auto-adjusting mode.
I’ve just now tested it with hooks clipped to the probes and the resistor leads—thanks for the tip! My resistance is still fluctuating, though; in the last 25 minutes, with no changes to the setup, I’ve watched it go from 97.5kΩ up to 108kΩ, and then steadily decline to around 45.5kΩ, all with an empty bed.
My mattress is memory foam, so I wonder if I’ve been seeing the foam decompress?
Perhaps, though I’m not sure how decompression would affect the weight, but perhaps it affects weight distribution. 25 min also seem long, but I don’t have a memory foam mattress.
I definitely see this with my memory foam mattress.
This graph is pressure experience by the FSR, but you can just think of it as the inverse of resistance. So for my setup, the resistance sky rockets right when I get out of bed, then decreases over time and levels out.
My theory is that the mattress rebounds up when you get out of bed (decreasing the weight on the FSR), then increases its weight on the sensor as the mattress fully relaxes.
Working on putting together a bed presence sensor using 24" FSR’s. Currently trying to get 1 sensor squared away completely, before I install the second. I have a memory foam mattress. The memory foam is transferring some of my wife’s weight onto my sensor.
Would it make sense to change out my resistor to “zoom in” on the voltages to give a wider range gap between me being directly over the sensor, and the incidental pressure transfer from my wife being there?
My brain tells me there would be less false positives because of increased accuracy where it matters.
Would a flat base work with these FSR sensors?
I searched this thread but don’t see anything about using this if you have a flat base (no slats). I have a tempurpedic matress and it was installed on a flat base. I believe it’s a pegboard on top of slats.
TIA
I imagine that would work fine. I have a stiff metal box spring my mattress is on. Ended up laying an 8" wide piece of plywood across it between the box spring and the mattress to have a place for the sensors. It doesn’t have any issues picking up pressure.
Sorry if this is a stupid question.
As a European I don’t recognise the symbol used at r2.
Thanks for all the write up!
There are two parts, an FSR and a resistor. You recognise the resistor so what do you reckon the other symbol is?
It’s not a cultural phenomenon. It’s electronics. 
In which case, why not label it as such and prevent any further confusion 
I’m closing this topic as it is no longer the best bed presence detector and I no longer use it or support it. I use this: Bed Presence for ESPHome by Elevated Sensors
Seeing that reddit found this post and is making up conspiracies…
Tom does not make the device linked above.
