esphome-pressure

This is a custom device for reading differential pressure. The most useful example I can think of is monitoring your pressure drop across your air filter. This is a great way to know when to change your filter.

It is based on an ESP32-C3-MINI, which has native USB-C for flashing.

This specific board has a sensor that can handle +/- 0.5kPa, which is about 2" of pressure drop. Most HVAC systems are designed to have a pressure drop of 0.1" (0.025kPa).

What's included

A fully populated PCB and screw terminal header. The case is NOT included.

Power Supply

It can be powered by USC-C, or, by a wider range of input voltages on the screw terminals. It was designed for 24VAC, which is a common voltage used in HVAC systems. It can also work with a broader range of both AC and DC input voltages. The absolute maximum voltage for the switching regulator is 40VDC, which means up to around 28VAC. The minimum DC is approximately 9VDC.

It has a 500mA polyfuse directly off the screw terminal inputs to protect your HVAC system. The USB-C port is unfused and should be protected by the upstream device.

Flashing / Programming

The USB-C port can be used to program. The first time, the reset button must be held. After this, all subsequent programming does not require access to the button.

There is also a header for the typical serial flashing with GPIO0(9) and EN exposed. It follows my eflashy32 pinout.

Enclosure

The PCB will fit inside a Hammond 1593KBK case. You can either cut (CNC) or 3D-print the faceplates. I also offer black PCB panels. You can superglue some magnets in the case to have it stick to your HVAC system.

Damage

Specifications:

• Up to 5X rated pressure is unlikely to cause issues
• Between 5X-10X rated pressure, the sensor might gain a permanent 'offset'
• Above 10X it is likely to burst and/or be permanently damaged

Setup guide

1. While holding the button, plug in the USB-C cable to your computer. This will put the device into programming mode. Holding the button is only required the first time you flash the firmware, or if you really mess something up. Future updates can be done over WiFi, or without needing to push the button.
2. Flash esphome using the sample esphome.yaml file. You will need to change the wifi settings to match your network. You can use a secrets.yaml file to keep your wifi password out of the main file, or you can keep it hardcoded into the main file.
3. Power-cycle the device, and you should be able to see the device shortly in Home Assistant.
4. With both ports unconnected, make a note of the value of the sensor.
5. For example, if your sensor is reading -40Pa when the ports are disconnected, you can set the offset to 40 to zero out the sensor in the esphome.yaml file.
6. Reprogram the device with the new offset. It should now report 0Pa when the ports are unconnected.
7. Using some tubing, connect the ports to the pressure points you wish to measure. For example, you can connect one port after the air filter, and the other to the return air duct. You can then monitor the pressure drop across the filter.

Note the sensor accuracy is +/- 2%. It is quite sensitive to pressure changes, so you may with to use other esphome filters in order to smooth out the values.