Design Raspberry Pi "Hat" Printed Circuit Board (PCB) for Sensors

[keenanjohnson]

A big way to drive the cost of the Frog down is to design a custom circuit board that contains some of the electronics, instead of buying multiple dev boards. We should explore this option :)

[keenanjohnson]

@lwbantoto has been taking the lead on this, so assigning this task to him :)

[daveb377]

Is this a Pi-Had or a PCB for the compute module?

[lwbantoto]

@daveb377 it's a Pi-Hat! It will be a stackable PCB

[daveb377]

SO a Pi Hat with a Sensiron sensor and a barometer? What else needs to be on there? Battery Interface/Solar power panel hookup?

[keenanjohnson]

Probably eventually a battery / solar hookup, but we'll need to figure out how to reduce the power consumption from the processor before that makes sense due to the lack of a sleep mode in the Raspberry Pi.

Yes the session sensor, barometer, and a GPS sensor are the intent for this hat.

[daveb377]

I spent 20 minutes looking for a Pi hat with those sensors with no success. I'll take a look at a board design, it doesn't look too difficult, although I might have some Pi related questions. First I need to out a Kicad problem with another project, it might be a week or two.

[keenanjohnson]

Sounds good! Reach out with any questions!

[daveb377]

@keenanjohnson - What sort of requirements are there on the CO2 sensor? The Sensirioin part is fairly large and expensive, and I'm wondering if there's a smaller part that would work? I'm trying to fit everything onto a Pi uHat for the Pi Zero, and it looks like it will all fit.

[keenanjohnson]

Hey @daveb377 we don't have any hard requirements on the Sensiroin sensor persay as we're still trying to identify the exact requirements from the data scientists. However, here are the loose requirement set:

• Humidity and temperature measurement ( The sensirion part includes an on board temperature and humidity sensor which is really important for the data analysis).
• A CO2 PPM accuracy of +/-30 PPM
• Good temperature stability
• NDIR sensing technology

If there is another part that fufils these requirements at a lower cost / size, I'm definitely open to it, but haven't found it yet.

It's great that you are helping to tackle this, but here's a few other key pieces of information for you that might make the Hat concept obsolete.
1 - We've switched in the BOM to the Raspberry Pi 4 CM4 module which includes a much higher gain antenna given I had some wifi connection issues with the small on PCB antennae on the Raspberry Pi Zero. So if we stick with the Hat format, we should probably size it for a normal raspberry pi.
2 - In another task, we've been working on a new enclosure concept to 3D print the full enclosure. Right now our concept has trended towards placing the sensors in a different enclosure section than the Pi, so I'm not if the hat concept really makes sense anymore? I'm open to people's opinions on this :). It would certainly make the whole package smaller if we did pursue it :)

[lwbantoto]

@keenanjohnson Are we satisfied with the humidity and temperature measurements from the Sensirioin part? Perhaps we should add our own temp sensors (thermistor) and humidity sensors on-board.