I am currently designing a device that will take measurements from a load cell that is in tension. I am using a v1.0 NodeMCU device that features an HX711 load cell amplifier and is running off of battery power. In order to conserve that power, I am wanting to be able to put as many parts of the device as possible into a sleep of some level when there is not a load on the cell. Then, I would like the device to be a be able to wake up when a load is applied and it goes into use. Going into a sleep will be simple enough, if the device is getting a reading around zero for a period time, it can enter sleep. Other notable hardware involved on the device will be a real-time-clock and an accelerometer.

From what I have already tried to look up, there doesn't seem to be any good way to use the load cell to get this action. The only idea I have been able to come up with for how to activate the device without having to wake it up extremely often other than a manual switch or checks very often came from this question. It suggests using a vibration sensor like this, which is how bathroom scales put themselves to sleep.

While I think it might be possible to use a vibration sensor to wake up the device, I am not sure if the loads involved and use case will disallow me from using one. Are there any other sensors or methods that could be used to achieve goals that I have for this device?

  • use a switch that closes when the scale deck is loaded – jsotola Jun 17 '19 at 16:04
  • use an ESP32 and a ULP processor routine to monitor the input. – dandavis Jun 17 '19 at 17:28
  • @dandavis After doing some research, that does seem like a really good option. The only issues that I can see running into is that the HX711 uses digital inputs and I have no idea how I would use assembly code to measure off of the HX711. What are your thoughts? – Rian Simpson Jun 17 '19 at 19:04
  • well it does make it a lot more complicated. the latest arduino lib helps somewhat, giving you some macros for common situations, one of which is reading an input state. i've not used it though, so i can't really explain it, i'm just aware of the broad possibilities it provides. – dandavis Jun 17 '19 at 20:17

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