I picked up one of these bed sensor pads to see if I can get it to work with HA. The pad has a 4-conductor wire, red, black, green, and yellow.
Red and black always have continuity between them as do green and yellow. Pressure on the pad doesn’t seem to affect this.
Anyone out there used one of these before and/or able to shed some light on what readings I should be looking for with the multimeter?
I have a pressure mat that has 4 cables (all black) but I only use 2 of the 4 and they are just attached to an aqara leak sensor set in occupancy mode which works pretty much flawless since setting it up.
You just need to see what 2 of the 4 will allow a closed circuit when pressure is applied.
One of those wire loops is there exclusively to detect if the device has been cut (for alarms).
Still struggling with this one. I’ve got the four wires each hooked up to a GPIO on an ESP32 and the voltage readings don’t really give me any indication when someone’s in bed (see graph below).
Green/Yellow have continuity as do Black/Red. I’ve tried connecting G/B, G/R, Y/B, and Y/R and don’t get any significant readings across them with a multimeter when there’s someone in bed.
Anyone have a suggestion for a next step that’s not “Return the thing to Amazon”? 
You’re not supposed to be connecting those wires directly to GPIO. What you’re supposed to be making is a resistor network that allows you to sense voltage differences in the range of 0–3.3V and therefore measure the change in resistance.
Hang on…
Then you will have a sensor that will get you a variable resistance or variable voltage. When the resistance goes below a certain setpoint, that means detection.
On top of that you can add debouncing using the delay on and delay off ESPhome constructs.
Here is the schematic of my bed sensor:
Note the bed pressure sensors are VR1 and VR2.
Here is the YAML
substitutions:
name: "master-bedroom-bed"
friendly_name: Master bedroom bed
esphome:
name: ${name}
friendly_name: ${friendly_name}
name_add_mac_suffix: false
esp32:
# XTVTX ESP32 (wroom)
board: nodemcu-32s
framework:
type: esp-idf
logger:
level: debug
logs:
esp32_ble: debug
sensor: info
mdns: debug
adc: info
resistance: info
internal_temperature: info
# Enable Home Assistant API
api:
encryption:
key: "<SUITABLE ENCRYPTION KEY>"
ota:
- platform: esphome
password: "<SUITABLE OTA PASSWORD>"
wifi:
reboot_timeout: 120min
networks:
- ssid: !secret wifi_ssid
password: !secret wifi_password
esp32_ble_tracker:
scan_parameters:
active: true
bluetooth_proxy:
active: true
number:
- platform: template
optimistic: true
id: resistance_threshold_for_occupant_1
name: Resistance threshold for occupant 1
min_value: 0
max_value: 212184185438208
step: 1000
icon: mdi:omega
entity_category: config
unit_of_measurement: Ω
restore_value: True
- platform: template
id: resistance_threshold_for_occupant_2
optimistic: true
name: Resistance threshold for occupant 2
min_value: 0
max_value: 212184185438208
step: 1000
icon: mdi:omega
entity_category: config
unit_of_measurement: Ω
restore_value: True
binary_sensor:
- platform: template
id: occupant_1
name: Occupant 1
device_class: occupancy
icon: mdi:bed
lambda: |
if (id(variable_resistance_1).state < id(resistance_threshold_for_occupant_1).state) {
return true;
}
return false;
filters:
delayed_off: 5s
# on_state:
# - if:
# condition:
# lambda: "return id(occupant_1).state;"
# then:
# - lambda: >
# id(occupant_1).set_icon("mdi:bed");
# else:
# - lambda: >
# id(occupant_1).set_icon("mdi:bed-empty");
- platform: template
id: occupant_2
name: Occupant 2
device_class: occupancy
icon: mdi:bed
lambda: |
if (id(variable_resistance_2).state < id(resistance_threshold_for_occupant_2).state) {
return true;
}
return false;
filters:
delayed_off: 5s
# on_state:
# - if:
# condition:
# lambda: "return id(occupant_2).state;"
# then:
# - lambda: >
# id(occupant_2).set_icon("mdi:bed");
# else:
# - lambda: >
# id(occupant_2).set_icon("mdi:bed-empty");
button:
- platform: restart
name: Restart
entity_category: diagnostic
icon: mdi:restart
- platform: safe_mode
name: Safe mode restart
entity_category: diagnostic
icon: mdi:restart-alert
sensor:
- platform: uptime
name: Uptime
entity_category: diagnostic
- platform: wifi_signal
name: "Wi-Fi signal strength"
update_interval: 10s
entity_category: "diagnostic"
- platform: internal_temperature
name: "Device temperature"
update_interval: 10s
entity_category: "diagnostic"
- platform: adc
id: resistance_voltage_1
name: Resistance voltage 1
pin: GPIO35
attenuation: 11dB
accuracy_decimals: 5
update_interval: 0.2s
filters:
- median:
window_size: 25
send_every: 5
send_first_at: 1
- calibrate_linear:
- 0.142 -> 0.0
- 3.171 -> 3.33
entity_category: "diagnostic"
disabled_by_default: True
- platform: resistance
id: variable_resistance_1
name: Variable resistance 1
sensor: resistance_voltage_1
configuration: UPSTREAM
resistor: 462kOhm
reference_voltage: 3.33V
icon: mdi:resistor
entity_category: "diagnostic"
disabled_by_default: True
- platform: adc
id: resistance_voltage_2
name: Resistance voltage 2
pin: GPIO32
attenuation: 11dB
accuracy_decimals: 5
update_interval: 0.2s
filters:
- median:
window_size: 25
send_every: 5
send_first_at: 1
- calibrate_linear:
- 0.142 -> 0.0
- 3.171 -> 3.33
entity_category: "diagnostic"
disabled_by_default: True
- platform: resistance
id: variable_resistance_2
name: Variable resistance 2
sensor: resistance_voltage_2
configuration: UPSTREAM
resistor: 470kOhm
reference_voltage: 3.33V
icon: mdi:resistor
entity_category: "diagnostic"
disabled_by_default: True
Thank you so much for that detailed reply. I finally had time to dig in to this and replicate your circuit (I think) and I’m not getting the results you describe.
I’ve tried with every permutation of the orange and brown wires with the R/B/G/Y wires from the sensor pad, but I think the yellow and green are the correct pair.
Regardless, the logs show the same values over and over, even with pressure on the sensor:
[12:10:04][D][sensor:093]: 'GPIO5': Sending state 3.10700 V with 5 decimals of accuracy
[12:10:04][D][resistance:039]: 'Variable resistance 1' - Resistance 33733.5Ω
[12:10:04][D][sensor:093]: 'Variable resistance 1': Sending state 33733.47656 Ω with 1 decimals of accuracy
[12:10:06][D][sensor:093]: 'GPIO5': Sending state 3.10700 V with 5 decimals of accuracy
[12:10:06][D][resistance:039]: 'Variable resistance 1' - Resistance 33733.5Ω
[12:10:07][D][sensor:093]: 'Variable resistance 1': Sending state 33733.47656 Ω with 1 decimals of accuracy
[12:10:09][D][sensor:093]: 'GPIO5': Sending state 3.10700 V with 5 decimals of accuracy
[12:10:09][D][resistance:039]: 'Variable resistance 1' - Resistance 33733.5Ω
[12:10:09][D][sensor:093]: 'Variable resistance 1': Sending state 33733.47656 Ω with 1 decimals of accuracy
[12:10:11][D][sensor:093]: 'GPIO5': Sending state 3.10700 V with 5 decimals of accuracy
[12:10:11][D][resistance:039]: 'Variable resistance 1' - Resistance 33733.5Ω
[12:10:11][D][sensor:093]: 'Variable resistance 1': Sending state 33733.47656 Ω with 1 decimals of accuracy
Here’s my sensor config:
sensor:
- platform: adc
pin: GPIO5
attenuation: 12dB
name: "GPIO5"
id: resistance_voltage_1
icon: mdi:bed
accuracy_decimals: 5
update_interval: 0.5s
filters:
- median:
window_size: 25
send_every: 5
send_first_at: 1
entity_category: "diagnostic"
- platform: resistance
id: variable_resistance_1
name: Variable resistance 1
sensor: resistance_voltage_1
configuration: UPSTREAM
resistor: 470kOhm
reference_voltage: 3.33V
icon: mdi:resistor
entity_category: "diagnostic"
Any suggestions? Is my circuit even correct?
Did you first determine which pair of wires actually changes resistance with a multimeter?
You shouldn’t swim before you can walk.
Yes, the green and yellow pair changes resistance when I attach a multimeter and apply pressure to the pad.
Simplify.
Skip the capacitors for now.
You should see the ADC value change up or down when you compress the resistance. It’ll be noisy because of no capacitors, but at least you can confirm it’s happening and you can add the caps later.
Also, what is the range of resistances your thing goes over? You may have to select a different resistance to get a good ADC measurement.