E-ink hat & photoresistor

Hi all,

I use a number of film cameras that do not have any sort of built in light meter so I’m looking to build one that can slot into the hotshoe of the camera. Just a tiny device that can sit on top of the camera and display some sort of lux or lumens value along with suggested exposure settings i.e. 1/50 sec at f/8 etc.

I would love to use an e-ink display for this as I think it would allow for great battery economy and a small form factor. However they all seem to be hats leaving none of the gpio pins on most relevant boards free to attach a photoresistor.

Would anyone have any advice as to how I could achieve this? Essentially I think I just need a microprocessor of any kind (a pi pico?) with an e-ink display, a photoresistor (and a way to connect it) along with a tiny lipo battery.

Thanks in advance for any help!



Hi Sam,

Welcome to the forum!! Sounds like an interesting project!

While most of the HAT/shield type modules ‘take’ most of the pins they usually arent connected and can be used for other tasks, check out the picture down in the description of the E-Ink module for the Pico:

The voltage divider for the photoresistor could be soldered into the analogue pin on the pico and the rest of the voltage divider hot glued

Combining that with a LiPo-shim should get you all of the features you want!

To physically connect everything you could go for some longer headers then cut them down once all of the parts are soldered together.

I’m keen to see how you go!

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Hi Liam!

Thanks so much for your reply. Great to know about the pins and I especially appreciate that handy diagram!

All makes sense to me however if you have time I would appreciate any more details/clarity around:

The voltage divider for the photoresistor could be soldered into the analogue pin on the pico and the rest of the voltage divider hot glued

What kind of voltage divider would be appropriate/necessary here? Just a resistor?

I’m putting together a parts list based on your advice and so far have the following:

How does this look to you? Am I missing anything??

Thanks again!


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Hi Sam,

You list looks good! Ooops, it also seems I forgot to link the LiPo Shim, there is one for the Pico and the Pi computers, you’ll want this one here: Pimoroni LiPo SHIM for Pico | PIM557 | Core Electronics Australia
You wont need the Micro LiPo either! If you plug a USB cable into the Pico it will charge the battery!

You’ll also want to grab some resistors if you dont have some already: Resistor Kit - 1/4W (500 total) | Sparkfun COM-10969 | Core Electronics Australia

To get a reading from a photoresistor(also known as an LDR) you’ll want to connect it like this: Using a Photocell | Photocells | Adafruit Learning System
The 10K resistor should still give you a good voltage swing as the LDR picks up more light.

If your build wasnt so dependent on being small I’d recommend checking out the PiicoDev Ambient light sensor (the PiicoDev expansion board will use a fair bit of space)


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Hi Liam,

Thanks so much for your help!

All of this makes sense. Looking forward to ordering this parts and getting started on the build!

Thanks again,


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