Load Cell Project- Squirrel Feeder

My partner and I are considering make a squirrel feeder for our independent study project for our Adv Biology class. We want the feeder to be able to measure the weight of the squirrel and collect the time that squirrel is there for us to get the data at a later time. The feeder will be put into a nearby nature reserve for a max of 30 days to a min of 10 hours (depends on the battery life of the feeder). What is the feasibility of making a load cell to calculate the weight of each squirrel?

We have no experience using arduino, but we do have plenty experience with working on robotics, manufacturing, and some basic programming. We have access to a DFRduino Uno R3 and a arduino part kit. We also have a CNC mill and 3d printer, along with a metalworking lab. A max budget would be around $50 for parts we don't already have.

I have researched a little bit on how to make the load cell but we need more guidance on putting all the pieces together. Any help would be greatly appreciated.

If it can be avoided, you really don't want to build your own load cell. What do to expect the maximum weight to be? Feeder, food, squirrel(s)?

The load cell can be used for both measuring the weight of the squirrel, and the time it's there.

Indeed it may be really hard to build your own load cell - buy that part, then construct a nice little scale out of it that you place where the squirrel sits while feeding.

Add a real time clock so you not only know how long the squirrel feeds, also when it does so.

You'll need an SD card or so to store the data. Maximise the amount of data collected; minimise the on-site data processing. If you store data every second as timestamp (4 bytes - seconds since epoch) and weight (2 bytes - make it into an integer) you can store a lot of data on a few GB of SD card.

Consider a solar panel to improve on your battery life. Putting the arduino to sleep in between readings (even at 1-second intervals and writing to SD card it'll be idle most of the time) may be another solution to improve on that.

Hi there,
Here's some parts I've used in a project like this.

Get a cheap $10 food scale from Amazon. Something like this:

Use the scale as the mechanical portion of the squirrel scale. The scale has 4 "load cells" at each corner, and the platform can be reused in your project so you don't have to do a lot of mechanical design work. Just make sure the supports put weight on the loadcell evenly, perhaps make a suspension platform, scale on top, and then feeder on top of scale.

Take the scale apart, but leave the 4 load cell and as much of the wiring as possible. Just disconnect the wires (3 wires per loadcell) from the brains. Then you can get one of these loadcell amplifiers from Sparkfun or ebay. You'll want to get the HX711 module as well as the load cell combinator module.

https://learn.sparkfun.com/tutorials/load-cell-amplifier-hx711-breakout-hookup-guide

And just use that tutorial to read digital weight data from the load cell module. I'd recommend a Arduino Pro Mini that's small enough to fit easily.

Lots of other considerations mentioned by others. I'm not sure what your wake up scheme should be. Wake up every few seconds and read the scale and write to SD card? Also, uneven distribution and moving squirrel might require some data manipulation afterwards. You'll probably want wake up more often when the weight of the feeder is high, to get more resolution during squirrel event to average out bad readings. And then when squirrel gets off, go back to a slower wake rate.