Automatic solar hedgehog/pet feeder

Summary

We started leaving some snacks out for our local hedgehogs. They liked this, and then we felt bad when we weren't around. So I designed this.
It's designed around kitten biscuits like https://www.sainsburys.co.uk/gol-ui/product/new-355373-44/sainsburys-2kg-complete-nutrition-kitten-with-chicken-2-18-months-cat-food because, well, read the customer reviews, but the exact size and shape doesn't matter too much. In fact that stuff seems to alternate between 5mm chunks and 10mm chunks from month to month. It's probably fine with fish food or whatever too. Just fill the drum compartments to whatever level you think is right for whatever you're feeding. I find about half full is enough to provide a light supper for the 2 or 3 hedgehog visits we get each night.

Design and operation

It's laid out so that one rotation of the gear with the cam advances the drum one segment. The cam hits the switch to signal when to stop. I have it release one compartment each day just after sunset* but you could make it do whatever you want. The sections are quite generous so portion size can be adjusted from a big meal to just a snack. The drum is good for 14 feeds between reloads.

*- Version 1 dropped the food at the same time each day but as the nights drew in we had some really disappointed hogs.

The microswitch recess takes the standard size you see everywhere. I used the type with the roller on the end but it would work with most flavours. You might need to bend the arm a bit but that's normal.
Alternatively there's a recess for a 2x5x10mm magnet in the bottom of the gear and a channel for a reed switch underneath. So use whatever you have in the parts bin.

I used a Firebeetle ESP32 because of the built in LiPo handling and lower power use in deep sleep mode. Code included if you choose to do the same but you could adapt to use whatever you have to hand. All it needs to do is decide when to feed (time, button press, motion sensor, whatever you like) and turn the motor until the switch changes (debounced) state and back again. I've added a few unnecessary features for monitoring, so mine wakes up every half hour and posts battery voltage and stuff to iotplotter, then decides if feeding time has passed and feeds if yes. But the basic requirement would make a really good first arduino project so by all means copy my homework if you want but if not, grab whatever micro you prefer and dive in.

Parts needed

Old storage box

Skip this if you're using it in your house to feed a pet.
Needs to be transparent, if you want solar power to work out. And big enough that cats can't reach the food but small enough that cats won't go inside. Cut an entry hole in the side about 10cm across.
A few options are available to attach the machine to it so it can't get shoved around. Two brackets are provided that hook onto the fixing provided which just needs a hole in the box to screw through, but feel free to design something else if they don't suit. You'll want it attached somehow because hedgehogs are vandals. I've provided the bracket I re-used from another project so if it looks like it wasn't designed for this, well, it wasn't. But it works. Feel free to design your own solution. 

Solar panel

Designed for a "2W 6V" solar panel - 110 x 136 mm nominal size, but you could make an adapter that slides into the slots and holds whatever panel you have in the parts bin. It doesn't need that much juice to keep the battery topped up for half-hourly status checks and one feed a day.

TT gear motor

Readily available

Power FET

Or beefy transistor, or motor driver, or something else to let your microcontroller drive the motor. I used a IRFL44N because I had some, not because it's the only solution.

Microswitch

I used the kind with a roller on the lever but almost any of the usual size will fit
Alternatively there's an option to use a reed switch and a 2x5x10mm magnet in the recess in the gear to achieve the same result. Just needs something to signal when the gear has made one rotation.

Microcontroller

You do you. I like the Firebeetle ESP32s because of the built in LiPo handling and tiny power use in deep sleep. Beware any microcontroller with a garbage voltage regulator that draws loads of power even in sleep modes. Those don't play well with solar powered projects.

Battery

Recovered from an abandoned vape

Screws

A few M3 screws. Nothing exotic. Self tappers would probably be fine too. Just make sure the drum turns freely but can't ride up on bits of food and get jammed.

Power switch

Hole and slot for optional power switch and button that you might want to program to do stuff. Cover with tape or glue, or fill them in in your slicer if not needed. I used a switch recovered from a solar garden light. Those things are one of the cheapest ways to buy parts.

Printing tips

The drum will really want to warp. If you can't get it to stay stuck to the plate, flip it upside down. There are thin slots to help reduce the stress in the walls if printed that way up.

You might want to use concentric top infill or ironing on the cover plate so that the food moves a bit smoother over it as the drum rotates rather than being grated across a rough surface.

If you put this in a transparent box in the sun in a warm climate in summer, it will get really hot. PLA will lose a lot of strength and some bits will slump. I'd recommend PETG for that scenario but don't be too put off. I've tried to design it so that the important bits are supported by enough material so PLA should be fine if it doesn't get too toasty.

Code

I've attached what I used for ESP32 but that should be adaptable to whatever controller you have laying around.
If you want all the iotplotter stuff and callmebot stuff you'll need to have/make an account on each but that's quite easy. If you don't, just comment it out. You might need to grab some libraries too.
If you want to use a different controller or start from scratch, that should be easy too. Would make a good first arduino project.

Code includes the option for an additional button for testing; hold it down while switching the power on to get into test mode, then press it to test-feed. Cycle power again to exit test mode.

Also kind of important to point out my ESP32 is set up with an internal voltage divider enabled to tell you the battery voltage on an analog pin. There are tutorials online about this. Follow the one for your board, and if there isn't one you'll need to make your own divider from some high-value resistors if you want it to report battery voltage, or just comment it out if you don't.

The main sketch is in the files and if you use it secrets.h needs to look like this. Fill in your own info.

const char *ssid = "yourssid";
const char *password = "yourwifipassword";
//iotplotter stuff
const String iotplotterAPIkey = "yourapikey";
const String iotplotterfeedid = "yourfeedid";
//callmebotstuff
const char* phone1 = "yourphoneno";
const char* apiphone1 = "apikey";
//work out sunset time
double latitude = yourlatitude;
double longitude = yourlongitude;