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heatseeknyc / hardware

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Doodles from @raphaelabrams #1

Open williamcodes opened 8 years ago

williamcodes commented 8 years ago

Take these changes or leave them, they are just doodles from @raphaelabrams, the engineer behind goTenna. Raphael recommends looking at digital temperature sensors to further reduce noise. Putting a second or third type of sensor onto the board just in case the first one doesn't work out could be a good insurance policy and would allow us to experiment with multiple sensors without printing more boards.

hrldcpr commented 8 years ago

Is it possible this didn't commit correctly? To me the board looks like this now, lots of vias with nothing connected to them: image What does it look like on your machine?

I like the idea of using multiple sensors, would have been fun to keep the old one on the board for comparison!

I don't think you can use digital sensors with XBees, otherwise I would have since the selection is much better. In sleeping mesh mode the XBees just sample periodically / can't do serial stuff, but can you ask @raphaelabrams if he knows otherwise? If we someday switch to microcontrollers on the cells then we can definitely use digital sensors.

hrldcpr commented 8 years ago

Oh, unless all those vias are what strengthen the ground plane?

williamcodes commented 8 years ago

Yes, all the vias are there to strengthen the ground plane and reduce noise. He said they're more effective the larger they are, but in some instances there wasn't room so he made them smaller.

Oh, he did other things that I didn't mention. He moved some things closer together to reduce the distance the signal had to travel through traces to reduce noise. He increased the size of the traces to reduce resistance and used the miter tool to round their edges. Apparently 90 degree angles are verboten for traces because the angle gets eaten into by the etchant during the wash and becomes narrower than you planned. In some cases it can cause the trace to short, although our traces are probably too wide for that to be a problem. He also tried to make the labels clearer by increasing the font size and positioning them in places that made it unambiguous what they were referring to.

He recommended we try out tempoautomation.com for production. Apparently you just send them an eagle file and they order parts, print the boards, assemble them, and ship them in 3 days, all for not much more than Advanced charges, and they might give us a discount if we name drop him. I'm gonna call them tomorrow. I'll also email Raphael your question about using digital sensors with xbees.

williamcodes commented 8 years ago

Oh also, he pointed out that on the data sheet it says our new sensor is extremely sensitive to light, so we'll have to make sure there's no light on the sensors when they're taking readings. Luckily those project cases are pitch black.

qelloman commented 8 years ago

I have quick question. What do you guys mean by noise exactly?

To my thought, I think we are using bottom plane as well as top plane other than signal path as ground, so it's enough for ground. Top plane part which is used for ground will do shielding for signal path, so we don't have to worry about coupling noise.

However, the chip is sensing the temperature by analog voltage from sensor, we should shorten the path and have many via to prevent from IR drop. Many via will help reduce voltage difference across ground path.

How much do we need to reduce noise? I think we need to have target..

Thanks, Doyun Kim

2015-12-04 0:01 GMT-05:00 William Jeffries notifications@github.com:

Oh also, he pointed out that on the data sheet it says our new sensor is extremely sensitive to light, so we'll have to make sure there's no light on the sensors when they're taking readings. Luckily those project cases are pitch black.

— Reply to this email directly or view it on GitHub https://github.com/heatseeknyc/hardware/pull/1#issuecomment-161877344.

williamcodes commented 8 years ago

Excellent point @qelloman, we should have a target. What do you suggest? I'm not actually sure what you even measure noise as. Decibels? What level of noise do other devices have?

qelloman commented 8 years ago

I would suggest the degree of noise should be socially accepted since we do this those who feel cold even with heating. Am I right?

If so, we need to provide the temperature data which is accurate enough to people. Honestly, Even with 1 degree error, we can't tell the difference. I'm not sure about this, but I don't think we need to put our priority on accuracy.

Thanks, Doyun Kim

2015-12-04 0:29 GMT-05:00 William Jeffries notifications@github.com:

Excellent point @qelloman https://github.com/qelloman, we should have a target. What do you suggest? I'm not actually sure what you even measure noise as. Decibels? What level of noise do other devices have?

— Reply to this email directly or view it on GitHub https://github.com/heatseeknyc/hardware/pull/1#issuecomment-161880699.

williamcodes commented 8 years ago

Okay so were measuring noise in degrees, that makes perfect sense. I also can't feel a 1°F difference in heat, but the law says that 54°F at night is illegal and 55°F is not, so if we want courts to take it seriously we need to be accurate down to 1°F. Actually we'd want our error to always be <0.5°F so we can round to the nearest degree and always be right. Luckily this sensor is rated to 0.1°F so as long as we don't introduce 5x more noise we should be good, right?

hrldcpr commented 8 years ago

Cool, thanks for all the hot tips @raphaelabrams! And yeah good points @qelloman!

I'll leave this unmerged until we have some time to decide on what changes we like and try things out, but it sounds like it all makes sense. I do want to ask him why getting rid of the power plane is good, though. Maybe an RF thing?