Temperature sensor accuracy

Hi Nico,

If required, these types of boards are quite neat to act as a sort of semi-reference. The accuracy is claimed to be +- 0.1 degrees C within a certain range. I have an older model that claims +- 0.3 degrees C I think.

They can be accessed via Bluetooth on mobile, and can show historical data as well. Link: https://www.newark.com/sensirion/sht4x-smartgadget/ref-design-board-temp-humidity/dp/74AJ2003 

Thanks for pointing that out, that's really accurate!
That would solve the problem of which sensor to trust as a baseline.

A man with a watch knows what time it is. A man with two watches is never sure

I've added it to my wishlist

ntewinkel said:

that's really accurate!

Looks like the reference design module uses the SHT40 sensor

Looks like the accuracy takes a bit of a deviation at around the freezing point, which you are interested in.

For comparison, the performance plot for the DS18B20 sensor

From the specs the performance is not much better, it's just different, at zero degrees for the sensor. But I think the problem is, without a reference design, the discrepancy will easily exceed those charts (for instance having the sensor powered up will warm it, or if its on a board then other components or drafts will heat or cool it. I observed that with a SHTxx chip too, where my layout was not the same as the reference board, and the measurement was off by more than the datasheet curve (by about 1-2 degrees from memory). The Sensirion board is their reference design, so should be more accurate - hopefully!

Edit: This was my layout, but it was not fit for purpose, the measurement was off by several degrees. Subsequently I changed the board shape to more closely reflect the reference design, but I've not tried the new layout yet.

New layout:

shabaz said:

I changed the board shape to more closely reflect the reference design

A half-way house might be something more like this

https://sensirion.com/products/catalog/SHT85

Interesting! Thanks for that, beacon_dave , that gives me more confidence in the ds sensor I have…. I guess there’s no avoiding science class if I want to verify it  

I think shabaz ‘s suggestion is still going to be a very handy reference to have around, given that it’s a complete system and easily portable.

Without the reference design (or comparing against known temperatures) I would have had no easy way to know if my board had a discrepancy. Comparing to that, I could easily see my design had quite a large error. 

Also, it's worth maybe not powering the sensor permanently. My first board has 3.3V permanently applied, but that's unnecessary, it could be better powered from a GPIO pin, to reduce heating from the power source. 

Plus, location with respect to other parts. Actually now I look at my (still-incomplete) KiCad project folder, it looks like I aborted having that sensor on the board, i.e. I removed it for the revision 2, simply because of the poor performance in revision 1, after considering proximity to other boards.

ntewinkel said:

I guess there’s no avoiding science class if I want to verify it

Ah, now you are talking...

Dolbear's law
https://en.wikipedia.org/wiki/Dolbear%27s_law

Synthesize a snowy tree cricket chirp to attract snowy tree crickets; then sample their chirp and apply Dolbear's law to get ambient temperature.

Sorted...

PS you need to do this before the hummingbird actually eats the 'thermometer cricket'.

shabaz said:

Also, it's worth maybe not powering the sensor permanently.

I was thinking about that when in your previous comment you mentioned the sensor warming up...

shabaz said:

having the sensor powered up will warm it

I'm actually not sure how I have that set up right now. The DHT module is also housed in a little case. well-vented but not in the open like the ds18b20 probe.

I think, for my purposes, if I can at least get the two sensors to somewhat agree, and have them be somewhat accurate as to when I need to worry about things freezing, then that'll have to be good enough. I think aiming for 0.5 degrees will be enough there.

I'm planning to carve out some project time soon for this. So far this year there have been too many distractions! Looks like I have to replace an axle on an ATV tomorrow.. how did I get suckered into that?   

I think I've heard a few crickets recently... that'll give me a good starting point. easy peasy 

ntewinkel said:

I think I've heard a few crickets recently

I only have grasshoppers here...

ntewinkel said:

that'll give me a good starting point. easy peasy

This should get you going

https://vanhunteradams.com/Pico/Cricket/Crickets.html

ntewinkel said:

Looks like I have to replace an axle on an ATV tomorrow.. how did I get suckered into that?

Has someone been overdoing the rock picking recently perhaps ? 

ntewinkel said:

Looks like I have to replace an axle on an ATV tomorrow.. how did I get suckered into that?

Has someone been overdoing the rock picking recently perhaps ? 

beacon_dave said:

Has someone been overdoing the rock picking recently perhaps ? 

Well, I DID overdo it the other day and have been too sore to continue haha ouch oops. But this is for the in-laws. We don't even own an ATV!!

Yesterday I was trying to bleed the brakes on his old truck (yeah I don't even do mechanics on my own vehicles anymore ), but all the bleeders are rusted in place except one. But it's a bit better. We noticed they were bad when we borrowed the truck a few days ago. Several months ago a brake line broke, so they replaced it and then never bled the air out!! I can't believe they left it like that! We told him to take it to the shop to get the bleeders replaced and get them to flush the fluid at the same time, so that's happening next week.

Seems as they get older (he's 84 now), they don't want to admit they can't do all the things they did when they were young, so they "start" the project and then "ask for help" which pretty much means we have to do it. We're slowly trying to get them to just take it to the professionals, but ugh, we often still get drawn into it.

I don't mind the occasional bit of tooling, and I guess it's a good skill to keep up

I just hope I make it to 84.   If I can do anything then, I'll feel victorious!

yep me too, and I hope I also have the kind of energy they have!

Project 14 theme - 'Help the Aged' 

Perhaps that's because they keep delegating the heavy tasks to others 

I am now the oldest surviving male in my family over the last three generations.

beacon_dave If we ever go that route, I've actually got an idea for a project.  That alone is unusual for me. 
I had better write it down - because we know in the moment... I'll for forget what the project was.

DAB Congratulations - sincerely.
My Dad was concerned about how long he would live.  His Dad died in his mid-fifties and he never knew his grandfather.
When he was in his early 60's, I reminded him that he was setting a new standard every day.
He lived to 83 - and a month.  Even in his last months, I would chastise him for chipping ice from his driveway.  "I gotta do something!", he would tell me.
"I get it, Dad.  Just do something else."

kmikemoo said:

I had better write it down - because we know in the moment... I'll for forget what the project was.

Just need a solution now to help remind you where you wrote it down...

Yes, the genes are not necessarily your friend.

Luckily on my mom's side, the men make it into their 90's, so my wife is hoping I take after that side of the family.

Still there are extenuating circumstances, my grandfather died at 55, but he lost a leg in WWI and was diabetic but would not eat right.

My father smoked for 60 years and then wondered why he had stomach cancer.

My older brother was exposed to agent orange in Vietnam, plus he was in numerous motorcycle accidents. I was very surprised he lived as long as he did.

So far I am trying to do the right things, keep my weight down, no nasty habits, and other than the heart attack, I am doing ok. I could probably do more, but I am a big believer in the quality of life, so I am not giving up my deserts or scotch any time soon.