What's more important to you?

What's more important to you?

And finally, what is the highest total component price that would be acceptable to you for a portable CO2 sensor? A low price would affect battery life and precision.

(For reference: The Aranet 4 costs around 200 EUR).

One more that comes to mind:

Would you rather have a device with modular components (like @adafruit's Feather system [1])? This would make it more hackable/repairable.

Or would you prefer one circuit board that has everything integrated? This would probably push the price and the size down.

1: https://learn.adafruit.com/adafruit-feather/overview

Time for another round of "blinry is clueless about #electronics" questions!

What's your experiences with JLCPCB vs PCBWay? I'm mainly interested in PCBA, which seems surprisingly cheap at JLCPCB!

How do you usually select specific components? For example, if I'm looking for a 4.7uF/50 V capacitor – which SMD package size would you use, which brand, and why? What's your process?

And when it comes to component placement, this seems like the most arcane art to me!

Below is the reference circuit for driving a Waveshare e-ink display – are there components for which it is important to actually place them close to each other on the PC? L1 and C4, for example? Are there rules of thumb here?

Is it possible/customary to place a via directly inside a solder pad? Seems like it would save some space, but maybe it's a bad idea?

#electronics

Okay, here's my best shot at a schematic for a low-power CO2 sensor based on an #ESP32-C6-MINI!

It still includes some questions in red, including:

- Should I add ESD protection to the USB D-/D+? Which kind?
- Should I add more filter caps to VBUS, the ESP's input, or to the button pins?
- In general, are the components I picked reasonable, or are there more standard MOSFETs, diodes or R/C sizes?

If someone more experienced in #electronics could help review this, I'd be extremely grateful!

Prepared a rough test order on JLCPCB yesterday to gauge the price – and learned that the ESP32-C6-MINI is not supported in their "Economic Assembly" Meaning that the assembly would cost a bit more.

Options:

- Hand-solder the ESP32 module
- Switch to the ESP32-S3-MINI (which, strangely, seems to support Economic Assembly)
- Switch to STM32 (whole new rabbit hole for me, and probably more difficult to build in connectivity?)
- Accept the price for Standard Assembly

#electronics

Back at my CO2 sensor project (an open-hardware Aranet 4 clone) this week! I finally made a PCB design – it's my first "complicated" design ever, so I feel very clumsy!

Changes I still wanna make:

- Flood the top layer with a ground fill, as well?
- Add mounting holes.
- Confirm correct placement of all parts in JLCPCB.
- Add a cutout to allow the e-ink screen to be connected from the other side.

If you have tips what mistakes to look out for at this stage, I'd be thankful!

Here's how I'm envisioning the entire device:

The battery will be at the bottom of the back side, with the ESP32 and CO2 sensor above it.

The e-ink screen connects to the center of the front side. Three buttons at the top can be used for interaction, the two at the back are for flashing. USB-C port at the side.

Progress shot for the day! Added cutouts and mounting holes, filled the front, modified trace widths, moved the charging LED to the edge, and fixed the battery polarity ().

While slapping on some labels, I noticed that the device doesn't have a name yet. If I call it "Aranot 4", they will sue me, right?

Placed an order for two testing boards at JLCPCB! Very exciting!

I added a solder jumper that can be cut to disable the LiPo charger, in case people want to power the device from some other source.

And I added through-hole pads for the voltage provided by the battery and for ground, to be able to measure power consumption more easily using a Power Profiler Kit II.

On a whim, I made the PCB yellow! Seemed fitting for a "CO2 Canary", which I guess is the name of the device now!

Now, I'm very curious to see whether the device will work! If not, I get to practice my hardware debugging skills, I guess…

Big thanks go out to everyone who has helped me up until this point! I learned so much working on this project so far!

@kicad is a lovely piece of software, I enjoyed using it a lot. Especially the "Design Rules Checker" gave me some confidence that I'm doing things correctly.

The PCBs should ship in a couple of days, I'll keep you updated!

Less than a week after placing the order, the boards have been manufactured, assembled, shipped, and are now in my hands!!

Happy with the look! For the "standard" assembly process, they add these little rails on the sides, which you can then break off.

This is the first time I've designed my own PCB! Now I'm really excited to see whether they'll work!

#electronics

The ESP shows up as a USB device, and I can flash the firmware on it! That's a good first sign that there's no fundamental problem with it! *relieved*

Good news: The e-ink display refreshes!

Bad news: It doesn't display what I want!

Maybe I just got pins wrong in the code? Gonna check after lunch!

I confirmed that, on my old hardware prototype, the display works with the Rust firmware I developed.

On my PCB, on the other hand, with minimal changes (pin changes), it's just snow.

I remember that I also had that problem when I first wired up the prototype, and the problem was a wrong "busy" pin, I think. So I still think it could be wrong pins? But I gotta investigate more.

@revk @twilliability

I *was* using a wrong "busy" pin! When I changed the pins in the firmware, I looked them up in an old version of the datasheet! Now it refreshes like it should! Also, I can power it using a LiPo! \o/

Next problem: The battery level indicator chip isn't reacting – when I speak to it using I2C, I get no response. I'll try to double-check the data sheet, to see if I wired it up correctly?

I was too curious about whether the CO2 sensor itself would work, and wired it up temporarily.

And it immediately did what it should, which makes me really happy! \o/ It really is a tiny CO2 sensor now!

(Yes, I breathed on it for testing in this photo! :P)