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Andrew_G
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Joined: 18/10/2016
Location: Australia
Posts: 872

Posted: 09:52pm 15 Mar 2017

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Hi,
I am "inching" my way towards finishing a project that uses an LCD Backpack to show Barometric Pressure (plotted over 3 hours and 7 days - measured by a BMP180) and temperature at four sensors (one being the BMP180, the others being 3x DS18B20). A RTC keeps track of time and shows it as Local (analogue) or UTC (digital) as per Geoff G's Superclock. All the components fit (just) in a jiffy box but I am not sure how much the BMP180 temperature readings will be influenced by being enclosed with the other bits and pieces.
I have no immediate way of measuring the "true" ambient temperature as the BMP180 is more accurate than the others.

Do any of you have any experience with housing the BMP180 with similar components and what are the options if it has to be externally mounted (I'm happy to perforate the jiffy box to assist circulation if that might help)?
Cheers, Andrew
(I'll post my code etc and as I am a newbie I am sure it can be improved . . .)

RonnS
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Joined: 16/07/2015
Location: Germany
Posts: 121

Posted: 06:38am 16 Mar 2017

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hi Andrew,

i can not wait to see more of your project

best regards Ron

Zonker

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Joined: 18/08/2012
Location: United States
Posts: 772

Posted: 03:29pm 16 Mar 2017

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Sweet..! Agree with RonnS... Post it up and show it off..!!

Useful projects are great...

matherp
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Joined: 11/12/2012
Location: United Kingdom
Posts: 10565

Posted: 11:21pm 16 Mar 2017

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Quote Do any of you have any experience with housing the BMP180 with similar components

My version has the BMP180 (BME280) hanging out of the box on 4 wires - definitely not the way to go

To keep it in the box, my advice would be to have ventilation holes top and bottom and to mount the BMP180 close to the holes in the bottom. That way the heat generated by the circuit will escape out of the holes in the top drawing ambient air through the holes in the bottom over the BMP180Edited by matherp 2017-03-18

Andrew_G
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Joined: 18/10/2016
Location: Australia
Posts: 872

Posted: 11:40am 17 Mar 2017

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Thanks for your replies. It looks to me that the temperature measured inside the hole-less box could be 2-3 (maybe more)degC higher than "true" (there is a fair lag in the temperatures stabilising so the experiments are ongoing). This is making me think that venting the box may not be enough - I'll report back.

Three questions arise:
1) The BMP180 measures the temperature so it can compensate its pressure readings - does this mean that pressure readings taken in an enclosed box (ie 3+ deg too high, possibly more in a cold environment) are improperly compensated - how does one alert TBS members to this? {Edit: No it doesn't! The compensation will be correct for the temperature measured; so the pressure should still be correct - TBS members can all relax. Andrew}
2) The RTC has a fairly bright LED - is there any way of disabling it (it will shine through the holes)?
3) My project is nowhere as sophisticated as the likes of Peter's and the code still has hickups (eg the configuration screens aren't working properly). But I do have a one pager that describes it and a schematic. When is the proper time to air it?

I'm off to drill some holes in a box, Cheers, AndrewEdited by Andrew_G 2017-03-19

Andrew_G
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Joined: 18/10/2016
Location: Australia
Posts: 872

Posted: 07:49pm 21 Mar 2017

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I seemed to have answered my own questions . . .
With the BMP180 enclosed in a Jiffy box using the LCD Backpack as a "lid" the temperature rise is about 3 degC.
With no box, but still only say 20mm from the LCD header connecting the two Backpack PCBs, there is say a 0.8 deg rise. No amount of perforations would have allowed adequate air circulation inside a box.

I've now housed the BMP180 in a small jiffy box well away from the LCD with a cable between the two boxes.

Cheers, Andrew

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