How to amplify delta of velostat sensor values

Tags: #<Tag:0x00007f77f95938c8>

Hi HA forum folks,

I built a few velostat sensors similar to this one: Bed occupancy DIY sensor (built by @tom_I) and I’m trying to “dial them in” so I can accurately set up a binary sensor to detect when I’m in bed vs. not in bed.

However, it appears that the difference is only 20Ω (going from 48Ω to 28Ω). When I use a 330Ω pull-down, the voltage range for into and out of bed is ~2.88V and 3.04V. Only about 16mV delta. :frowning: If I increase the pull-down to limit the current, it reduces the delta.

Since this is effectively a voltage divider for the analog input, I’m worried that if I drop the pull-down resistor below 330Ω I’ll be ramping up the standby current – theoretically if the velostat value drops to 0Ω, then I’m burning 10mA… not good.

Is there a way to amplify the delta between into and out of bed while not causing a bunch of extra current draw?

Thanks,
-Greg