Author Topic: Bloom Sky iOS Barometer might include an outside air temp factor  (Read 3910 times)

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Offline waysta

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Bloom Sky iOS Barometer might include an outside air temp factor
« on: February 22, 2016, 09:29:03 PM »
Bloom Sky reports two different barometer readings, possibly one is absolute, the other elevation corrected for our reported location (the "altimeter" reading).

The iOS Bloom Sky barometer reading is the corrected measurement.  Unfortunately, it does not seem to log anywhere. (The data portal and WU log the absolute value).

I have begun to collect iOS readings and to compare them to my RainWise barometer readings.  The RainWise readings have been checked against the nearby Mil airport and check well on CWOP.

I just a have a small number of data points so far from yesterday and today.  However, the line which is beginning to form on the attached graph is hinting at a temperature factor.  The graph shows the difference between the Bloom Sky iOS reported barometer and the RW WU value (in Hg) at about the same time (within minutes of each other) plotted against outside air temperature (deg. F).
« Last Edit: February 22, 2016, 09:37:45 PM by waysta »

Offline nincehelser

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Re: Bloom Sky iOS Barometer might include an outside air temp factor
« Reply #1 on: February 22, 2016, 11:17:04 PM »
Mine seems to be maintaining a steady difference regardless of temp... at least between 32F and 50F.

When calculating the absolute pressure from the baro sensor data, the operating temp of the baro sensor does play a factor.

Offline waysta

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Re: Bloom Sky iOS Barometer might include an outside air temp factor
« Reply #2 on: February 23, 2016, 07:09:02 AM »
When calculating the absolute pressure from the baro sensor data, the operating temp of the baro sensor does play a factor.

That is a good point.  It could be a wrong coefficient in the conversion formula, a bad part (e.g. out of spec), or their production run has more variation than anticipated.

Of course in an real world data there is going to be some "spread" in the plot, but interestingly, I think the width of the line is caused by the difference in the analog to digital converters step size (the size of the steps of the finest change as seen on the WU plots of the absolute pressure reading).

If the data continues to fill in roughly as a line, they have the raw data to make the correction because they report temperature with each barometer reading.  This is looking like another "fixable" problem.  Whether it could be cost effective to calibrate each individual barometer in production at this price point, I have no idea.
« Last Edit: February 23, 2016, 07:16:50 AM by waysta »

Offline waysta

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Re: Bloom Sky iOS Barometer might include an outside air temp factor
« Reply #3 on: February 23, 2016, 07:20:40 AM »
If others want to check their Bloom Sky barometer readings,

For each entry, jot down the
1) Bloom Sky iOS or web reading (not the WU or Bloom Sky data portal absolute values, although you could record them too),
2) Bloom Sky outside temperature,
3) some known local barometer value at about the same time from another wx station, or a nearest airport,
4) the date and time, and the difference between the two barometer readings. 

Take the data over a range of outside temperatures, and over several days.

I can post the excel sheet later, or if it's not too much data, I can plot it for you.
« Last Edit: February 23, 2016, 07:28:01 AM by waysta »

Offline nincehelser

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Re: Bloom Sky iOS Barometer might include an outside air temp factor
« Reply #4 on: February 24, 2016, 01:51:50 AM »
If the data continues to fill in roughly as a line, they have the raw data to make the correction because they report temperature with each barometer reading.

Usually the temperature of the baro sensor is embedded in the data from the baro sensor.  You don't to use the outside air temperature for calculating the absolute pressure as they are often different.  (e.g. an indoor barometer or heating due to the baro sensor being nestled among other heat-producing components).

I've no clue why you're seeing differences that seem related to temperature.  Mine seems to have the same incorrect offset regardless of temperature.

Offline waysta

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Re: Bloom Sky iOS Barometer might include an outside air temp factor
« Reply #5 on: February 24, 2016, 11:41:31 AM »
If the data continues to fill in roughly as a line, they have the raw data to make the correction because they report temperature with each barometer reading.

Usually the temperature of the baro sensor is embedded in the data from the baro sensor.  You don't to use the outside air temperature for calculating the absolute pressure as they are often different.  (e.g. an indoor barometer or heating due to the baro sensor being nestled among other heat-producing components).

I've no clue why you're seeing differences that seem related to temperature.  Mine seems to have the same incorrect offset regardless of temperature.

I think it is yet another Bloom Sky barometer instrument error.  Attached is the latest plot.  The plot shows that my reported barometer error [in Hg] (based on the iOS app reported barometer readings) is a strong function of outside air temperature.  Yes, I think that's right, the error could be in the sensor itself if it reports out a temperature corrected digital number (more likely the case these days).  Or, if the sensor makes an analog level that the Bloom Sky electronics digitizes, the temperature drift could be there. 

If others are not seeing the barometer error changing with temperature, this error could be unique to my Bloom Sky (it might be broken or otherwise out of spec.)

In any event, while I really like the Bloom Sky webcam and daily movie, this 0.2 in Hg level of barometer error, especially as now complicated by a strong temperature dependence, in my opinion, makes the instrument less suitable for crowd sourced weather information.  They need to deal with the barometer issues if they want to market a quality wx station. [ You are not allowed to view attachments ]
« Last Edit: February 24, 2016, 12:24:43 PM by waysta »

Offline nincehelser

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Re: Bloom Sky iOS Barometer might include an outside air temp factor
« Reply #6 on: February 24, 2016, 01:41:16 PM »
In any event, while I really like the Bloom Sky webcam and daily movie, this 0.2 in Hg level of barometer error, especially as now complicated by a strong temperature dependence, in my opinion, makes the instrument less suitable for crowd sourced weather information.  They need to deal with the barometer issues if they want to market a quality wx station. [ You are not allowed to view attachments ]

We could learn so much more if someone would just do a "teardown" and provide some pictures.

This is the best image I could find: https://ksr-ugc.imgix.net/assets/003/207/704/d8c221787ed3638ea772df4912890dd3_original.JPG?v=1422573303&w=639&fit=max&auto=format&q=92&s=759f12aac270438c952ba848415bda64

It's part of this Bloomsky Kickstarter update: https://www.kickstarter.com/projects/907431954/bloomsky-snapshot-of-your-weather/posts/1118582

I'm thinking the baro sensor is on the upper left of the board on the upper right, but I can't be sure.  I want to think it's a Bosch sensor as is in the iphone, but that might be wishful thinking.


Offline waysta

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Re: Bloom Sky iOS Barometer might include an outside air temp factor
« Reply #7 on: February 25, 2016, 11:11:24 AM »
Well, here is a new twist.  My Bloom Sky data on both iOS and WU is now usually hours old.  Just got a WU email too saying Bloom Sky has not updated in more than 2 hours.  As far as I know, this is the first time for hours delayed data since I installed mid January.

For several days, I was able to reasonably easily collect the data for my spreadsheet by looking at the iOS App barometer reading and the readings on the Bloom Sky and RainWise Weather Underground pages.

I sent my barometer observations to Bloom Sky tech support with a link to the thread here, by email (no reply, but it has been less than a day).

Now, it is more difficult to fill in the spread sheet because for long intervals, the iOS App (when I finally get it to update) reports hours old data.  Also, the RainWise WU page is updating within minutes, but my BloomSky WU page also now lags.

For example, at 11:04 local (est), both my iOS and Bloom Sky WU pages report 8:56 am, while RainWise was up to date at 11:04.

The problem is that the Bloom Sky iOS barometer value does not appear to log anywhere (it is different from the "other" different (possibly "absolute") barometer reading logged at WU and on the Bloom Sky data portal).  So, now I have to write down the old iOS data and go back to find the corresponding old data in the WU logs.  It is still doable, but one more step and another pain.

Also, as we get some warmer temps and I can fill in more of the temperature range, I can take some data for that range.  Now, I have to remember to go back and get it two hours later.  This is all manual recording, so I have not been able to auto-log, say every half hour or so, which would be an infinitely better way to make the chart.

The new hours old data could be caused by someone looking at the problem, or it could be just coincidence.  It is not WU, because the RW data is still updating, and both Bloom Sky sources show the hours delay.  It is disturbing none-the-less.
« Last Edit: February 25, 2016, 11:29:18 AM by waysta »

Offline waysta

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Re: Bloom Sky iOS Barometer might include an outside air temp factor
« Reply #8 on: February 25, 2016, 08:14:19 PM »

We could learn so much more if someone would just do a "teardown" and provide some pictures. ... I'm thinking the baro sensor is on the upper left of the board on the upper right, but I can't be sure.
  If that was the baro sensor (upper right in this pic, unused pads), it got cut, possibly for cost savings?  That part looks expensive.

I assume there is a baro sensor of some kind in there somewhere.  It would be pretty funny if they source the baro data from somewhere else (probably not).

It might be out in the sensor pod?  I did not disassemble that part near the screen.
« Last Edit: February 25, 2016, 08:48:18 PM by waysta »

Offline waysta

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Re: Bloom Sky iOS Barometer might include an outside air temp factor
« Reply #9 on: February 25, 2016, 08:17:06 PM »
top view

Offline waysta

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Re: Bloom Sky iOS Barometer might include an outside air temp factor
« Reply #10 on: February 25, 2016, 08:19:16 PM »
antenna and switches

Offline waysta

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Re: Bloom Sky iOS Barometer might include an outside air temp factor
« Reply #11 on: February 25, 2016, 08:21:23 PM »
battery an some sensor connections

Offline waysta

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Re: Bloom Sky iOS Barometer might include an outside air temp factor
« Reply #12 on: February 25, 2016, 08:22:43 PM »
first part opens with four screws (very tight)

Offline waysta

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Re: Bloom Sky iOS Barometer might include an outside air temp factor
« Reply #13 on: February 25, 2016, 08:31:23 PM »
Well, she's back online, at least for temp and humidity data.  Won't know if the camera still works until daylight tomorrow.  I put it back on a wood stand in the backyard. 

If it needs reseting once in a while, I sure as heck am not climbing to the roof, and taking down a pole each time while wearing a safety harness just to reset the WiFi connection!

Offline waysta

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Re: Bloom Sky iOS Barometer might include an outside air temp factor
« Reply #14 on: February 25, 2016, 08:34:33 PM »
fingers connect to these pads for the rain sensor;
interesting interlocking parts in back

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Offline waysta

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Re: Bloom Sky iOS Barometer might include an outside air temp factor
« Reply #15 on: February 25, 2016, 08:38:17 PM »
buttons and lights go in here
swivel for camera top
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Offline waysta

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Re: Bloom Sky iOS Barometer might include an outside air temp factor
« Reply #16 on: February 25, 2016, 09:10:09 PM »
(could U12 be a sensor, is that odd gold mark a port or just a pin 1 colored mark?)

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Offline nincehelser

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Re: Bloom Sky iOS Barometer might include an outside air temp factor
« Reply #17 on: February 25, 2016, 09:10:53 PM »
If that was the baro sensor (upper right in this pic, unused pads), it got cut, possibly for cost savings?  That part looks expensive.

I assume there is a baro sensor of some kind in there somewhere.  It would be pretty funny if they source the baro data from somewhere else (probably not).

It might be out in the sensor pod?  I did not disassemble that part near the screen.

What I was thinking might be the baro sensor was the wifi module.  I'm not sure what that removed part was, but it's labeled with a "J" which usually means a jack of some sort.  Perhaps it's something they only use for development.

Nothing's jumping out to me as the baro sensor.  Was there anything mounted underneath this board?

Offline nincehelser

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Re: Bloom Sky iOS Barometer might include an outside air temp factor
« Reply #18 on: February 25, 2016, 09:12:17 PM »
(could U12 be a sensor, is that odd gold mark a port or just a pin 1 colored mark?)

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That's what I'm thinking.  I'm not sure why it's gold, though.  It has about the right number of pins you'd expect.

Offline waysta

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Re: Bloom Sky iOS Barometer might include an outside air temp factor
« Reply #19 on: February 25, 2016, 09:13:13 PM »
The posts show both sides of the board.  The pics with the gold points engage the gold pads of the rain sensor.  The WiFi module is on the bottom of the board facing the underside of the rain sensor.

The pics where the antenna is visible show the top of the board.  The two silver electrolytic capacitors (470uf, 50V) are on the top of the board as well as the black IDC two row connector for the small board with the switches and the two white connectors for the battery and sensor connectors.
« Last Edit: February 25, 2016, 09:17:12 PM by waysta »

Offline nincehelser

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Re: Bloom Sky iOS Barometer might include an outside air temp factor
« Reply #20 on: February 25, 2016, 09:39:50 PM »
I can't make out any of the text on U12.   :sad:

Offline waysta

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Re: Bloom Sky iOS Barometer might include an outside air temp factor
« Reply #21 on: February 26, 2016, 12:32:23 AM »
There are other pics, but the conformal coating (only on one side of the board) makes it difficult to see any numbers.  I'm thinking that might just be a pin 1 marker.

On the other side of the board, there are two resistors RP1 and RP2 which might be consistent with some sort of pressure / amplifier / bridge circuit. 

The chip could be an analog amplifier for a pressure sensor element elsewhere.  A small analog pressure sensor element could be elsewhere on the board or out in the screened area with the temperature and humidity elements, or up in the top section somewhere too?

An analog signal conditioning stage would be entirely consistent with the temperature sensitivity I was graphing before it disconnected and played dead.

Not decisive by any means, but I've never seen a fully integrated pressure sensor without a well defined open port or window of some sort.

I continue to be amazed by the engineering contradictions.  Except for a few really terrible solder points (e.g. R84, near C33), the board appears to be very high quality.  Yet, the performance, at least of the barometer is entirely sub-standard, to a point where thousands of these as to crowd sourced barometer (as is) could in my opinion be a terrible disservice to amateur science efforts.

But, I do like the sky camera :)
« Last Edit: March 05, 2016, 05:21:21 PM by waysta »

Offline waysta

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Re: Bloom Sky iOS Barometer might include an outside air temp factor
« Reply #22 on: March 04, 2016, 08:51:03 PM »
I had another close look at the pictures, U12 looks like a flash memory.

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« Last Edit: March 04, 2016, 08:53:24 PM by waysta »

 

anything