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In recent weeks with winter setting in here in Iowa, I have found myself looking at my watch (a Casio G-SHOCK) to see the temperature, and of course it's not there. It's frustrating

So, the obvious solution is not to get a smart watch and spend a bajillion dollars, nor is it to get over myself and just accept that it's hella cold out, no. The solution is my new temperature watch!

Now, I know what you're thinking. Won't it just measure the temperature of my wrist. No, it won't. it's an open design with no case, so air is free to move in and out around the temperature probe.

I have designed a board and ordered it from OSH Park along with parts from digikey:

Can't wait to have this product in time for winter!

As always suggestions are always welcome.
I'm having a hard time puzzling out all the bits just based on the board. Care to share a schematic too?
wouldn't that have the slight disadvantage of not being able to be water resistant?
Honestly I thought this was going to be a "temperature watch about global warming!" topic. Laughing
Looks neat! Although I have to argue that a bajillion isn't a real number.
***TheLastMillennial runs

Any plans on mass production? Idea
Here is a (sorta EDIT:: Very messy) schematic:

I have no plans for mass production, and yes, it is not water resistant.
Botboy3000 wrote:
Here is a (sorta EDIT:: Very messy) schematic:
Well.. it's.. a slight improvement over not having a schematic at all? It kind of raises more questions about how this supposed to work though.

What's this supposed to connect to for power and whatnot? I assume that's the unlabelled 6-pin header, but what's the actual device there that appears to speak SPI and provides 5V with a pulled up reset line? I guess that's actually a 6-pin in-circuit serial programming header, but it also just raises more questions if it is (how do you not blow up the reset switch if it's pressed under normal operation, for instance?).

No idea what the parts for your temperature sensor or display are, so it's unclear if you really do want to leave the apparently-~3V inputs unconnected. I'm forced to assume they're parts that can safely operate on ~3 or 5V.

The layout on your crystal's load capacitors is frankly appalling. You should try to minimize trace length between the micro and oscillator, and definitely without branching traces like you have on C1. AVR042 may be helpful, because your layout fails to follow most of the guidelines. It'll probably still work because it's a pretty robust chip, but if it doesn't you'll have a very hard time working out why.
You have a floating reset pin. You should really have a pull up resistor on that reset button connection, unless you want it to continuously reset randomly? Also you should have a capacitor across VCC and GND on the microprocessor pins, 0.1uF or something. You should also add external power traces if you plan on using a battery (Why 5V logic and not a simple 3.3V lithium coin cell battery is the real question...) Anyway, good luck Smile
The schematic really wasn't meant to be shared, lol.

That 6 pin header is for programming the microcontroller, and I know it doesn't appear on the schematic (cause I didn't need it on the board) but there is battery connection.
I thought the reset pin was pulled up inside the chip? If not, it won't be that hard to add in a resistor to pull it up. I'm using a lithium ion battery from adafruit, so I'll see how the noise from that effects the performance.

I agree I do need to be better about designing for a reader, rather than just throwing things on the schematic Razz but I never planned to share this anyway. Thanks for the advice though!
So, I got the boards from oshpark, and after lots and lots of troubleshooting my arduino IDE I uploaded the code onto the microcontroller and it RAN! now, the atmega328-au was only running at 1Mhz so it was really slow. First question, what is the best way to fix this? I know one way is to upload a bootloader onto it which apparently sets fuses to make the thing work at 16mhz but when I tried to do that, it won't let me upload to the board anymore! like, anything. It worked once and now it says "Yikes! invalid device signature." what happened? it did get to the end of the program which looks like this:
Did you ever fix the reset line to actually have a pull-up? If it's not being reset correctly you'll probably get garbage back out.

What did you actually program to it? Using what tool? What are you trying to use now? The same tool(s)? There are a lot of bits controlling the device's behavior on coming out of reset and guessing wildly is going to be a waste of everybody's time.
Right now the reset line is being pulled up to +5V through a 1k pull up resistor. I programmed it with Arduino IDE using an Arduino Uno as ISP.

EDIT:: I have very exciting and also incredibly confusing news
I removed my 16Mhz crystal off of my watch board, and also it's capacitors, and tacked jumpers from the one on my UNO over to it (to see if the crystal was the problem.) it didn't work, but after I cut one of the jumpers (now only one wire going from one pin of the UNO's crystal to one of the pads for a crystal on my watch board) and that made it work.... and it yet doesn't work with no crystal. But, that leads me to ask is there a way to run the whole chip off of the internal 8Mhz clock? and also what is wrong with my setup of my crystal that makes it not work?

EDIT EDIT:: So it turns out the literal root cause of all my problems was a short across the two XTAL pins on the microcontroller. In an attempt to re-solder the 16MHz crystal back on the board, one of the legs fatigued off. Now I have a 16.9MHz crystal that I had in a junk drawer tacked on there, and it seems to be working just fine.
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