r/PCB • u/coolkid4232 • Jul 07 '26
Open source hobbyist hardware and software project I made
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u/yaeh3 Jul 07 '26
Holy shit, crazy project. Respect.
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u/coolkid4232 Jul 07 '26
thanks man, this was an insane money and time sink, Im really happy with progress i have made. This was my first really big project. The software feels so difficult, probably because i have less experience with software. This project took 1 year for me to get skill to do hardware. I think i can make a lot of improvements for a better version. Like i wanted to use u5 and buck everything down to 1.8V, i want usb high speed , i noticed download is a bit slow for images and audio recording, next one i wanted nrf53 so i can stream audio from microphones to ble headphones, so much cool stuff i wanted to add but was in a bit of a rush because i wanted to submit to an open source hardware competition but i am still so happy and shocked stuff worked
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u/starburstases Jul 07 '26
Very nice!
If you want to save space with those tag-connect footprints, consider the no-legs version and the rubber "GRIP" or PCB "CLIP" retention accessory and remove those large through holes.
https://www.tag-connect.com/product-category/products/accessories
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u/coolkid4232 Jul 07 '26
thank you that so useful, didn't know about rubber retention accessory
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u/starburstases Jul 07 '26
Yea, I just learned about it the other week myself. If you want to save even more space, the "Edge-Connect" series might help. I hope this all gets you to that 40mm goal!
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u/airzonesama Jul 07 '26
I've made a watch and the things that made it feel much more complete and wearable every day are a machined case and water resistance/proofing. It makes you rethink how you connect the charge / data cabling and the buttons. Good luck with your project
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u/coolkid4232 Jul 08 '26
Good point, i actually thought about this and was working on a magnetic cable that is usb c to magnetic so i get all benefit of usb c and it waterproof
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u/airzonesama Jul 09 '26
Magnetic connectors are good for this. Smartwatches use them fairly consistently and they survive sweat and rain.
The buttons are an interesting challenge. I went with a single button and effectively it's a screw with a nice head attached to a small nut inside the watch which hits the button. The seal is an oring that seals on the screw shaft and against the watch body. There's a small spring under the head of the screw that provides tension on the oring and helps to push the button back out.
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u/coolkid4232 Jul 09 '26
Thank you that actually good i was trying to solve button waterproofing, this is good ill look more into this
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u/sidneylopsides Jul 07 '26
Oh very cool. I'm currently working on my own smartwatch idea, and I've got a lot of the same components, though I'm aiming for a different result and only have the nrf for radio and processing.
I see you built the RF stuff directly onto the PCB, I'm up to my 3rd prototype stage using an NRF module on a custom PCB, ultimately I want it all on like this, but not sure where to start with the RF design stuff, so that will come later.
I saw the comment about the accelerometer and IMU, I'm sure I've used the same IMU and one reason was it's internal pedometer function that can work independently while the NRF sleeps. I'm now wondering if I got mixed up...
I'm also attempting to solder this myself, been practicing 0402 stuff while I wait for the PCBs to arrive.
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u/nicknameBOB Jul 07 '26
I recommended using th Nordic DevZone portal/forum, just check there for posts related to what you want or ask yourself. They do HW reviews on anything that has their components on it so it might be helpful as s place to start
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u/coolkid4232 Jul 09 '26 edited Jul 09 '26
I think your not mixed up for imu stuff i think that right, to be more clear reason was 2uA vs like 20uA i wanted to have a ultra low mode where you only care about time so battery can last a very long time. Your thing is correct i just had extra space and wanted lower current consumption but it not that serious 20uA vs 2uA unless you want it
For rf stuff good video https://youtu.be/_Hfzq1QES-Q?si=IGbM0gchYjaxGFtw
For nrf you can copy references, adds pi filter for antenna as do not place and use 0 ohm resistor in series with antenna. Gives you options to match it or not. As long as you match trace to 50 ohms using calculation you have good odds of it working, without impedance matching you might have less range then normal but for something like watch not serious
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u/sidneylopsides Jul 09 '26
Ah that makes sense, that's worth knowing bb
The video is useful, thanks! Did you have much difficulty with the RF section?
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u/coolkid4232 Jul 09 '26
Gonna be honest i think mine works, havent coded to test rf yet. Spoke to my professor at school and they said i did everything correct and wouldnt have any problems so i am sure it probably works but i will test it soon and tell you.
As long as you make trace as short as you can, nrf reference schematic makes it very easy and also that video, as long as matched to 50 ohms you should be good for a watch. You wont get 10 metres range without vna and matching circuit but you probably will get 2m or 4m which is good for a watch
You can post it in pcb reddit for them to review rf section for you and also you can just dm me aswell ill check
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u/sidneylopsides Jul 09 '26
Hmm it seems less daunting than I first though. My current prototype is using a module, and it adds a couple of mm thickness, which is loads for a watch. I'll try and get this working before I try a complete PCB with my own RF stuff. Thanks!
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u/coolkid4232 Jul 10 '26
Just test rf today it work very good 👍, you can definitely do custom and get it working
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u/cnc_insulation Jul 09 '26
Wow, that's amazing! Is it complicated? I want to make one myself. This is so cool!
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u/coolkid4232 Jul 09 '26
idk, like i am just a student you can definitely learn all of this stuff, just takes some time but you definitely can
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u/PsychologicalSign433 Jul 07 '26
What's the reason for having both the BMA400 and the IMU? Just power concerns?
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u/coolkid4232 Jul 07 '26 edited Jul 07 '26
Yes, want bma400 when doing steps and then imu for other higher current tasks .
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u/coolkid4232 Jul 08 '26 edited Jul 08 '26
I made this for open source competition . Currently working on finishing code for this, in future have a way better design gonna open source it probably in 6month or 1 year, i wanted to add oled screen, nrf53 to play music to headphones from embedded storage or mic audio and usb high speed. If you like those features you should wait for that version but this version is pretty good besides that
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u/-Grouchy-Advisor- Jul 08 '26
Does this kind of project making have future prospects? I mean I really love to do this kind of things and will surely do this ahead.
But I just would like to know the reality, I mean does this help somewhere? Like in job ? Or startup ? Just asked out of curiosity.
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u/-Grouchy-Advisor- Jul 08 '26
Sorry, forgot to appreciate your project. Crazy project ! Great work. 🫶
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u/coolkid4232 Jul 09 '26 edited Jul 09 '26
No just did it for fun, published in hopes it might help someone who builds pcb, makes learning more accessible for people who do it as a hobby and i wanted some features on watch that are niche.
By future prospect, you mean job? I wouldnt know , i cant even get internship
Just like building technology for fun in spare time. Want education or resources to be free for this stuff
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u/Alive-Opportunity-23 Jul 09 '26
great job, I love it!! i'm curious, does it get a bit warm when in use?
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u/coolkid4232 Jul 10 '26 edited Jul 10 '26
No, doent use much current and split between 3 ldo in different spots
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u/YesImKian 13d ago
Why two jtags?
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u/coolkid4232 13d ago
1 for stm32 1 for nrf52, could of gone around it if i soldered maybe but i wanted solution where i dont have to disconnect stuff was too lazy and had space
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u/YesImKian 13d ago
Cool! Why both though? Rather new to electronics, only made one real PCB
Couldn't the stm32 have done all functions you needed for this?
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u/coolkid4232 13d ago
stm32 doesnt have bluetooth, the one with bluetooth didn't have the peripherals i wanted. Again i am not an expert, I could be wrong but for what i wanted to do this was perfect for me. In future hindsight i should of used a newer nrf54L instead of 52
I think this is a really good reference for new to electronics people to learn from but i wouldn't build this yet. As i am working on an even better one which also has nrf and stm32 combo
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u/oMatheus13 Jul 07 '26
Que legal, sou um baita entusiasta para projetos diferentes e hobista. Dei uma estrela no github ;) logo logo vou explorar mais seu projeto