My "Sensor Board" for OpenXsensor

Development & General Chat for the superb openxvario project.

Moderator: rainer

Post Reply
sfabris
Posts: 8
Joined: Sat Jan 04, 2014 12:28 am
Country: Italy
Location: Vicenza

My "Sensor Board" for OpenXsensor

Post by sfabris »

Hi,

I'm following this project since the beginning.. In the last month I designed a small board with everything I need in order to replace the complete mess of Arduino's and break out boards.

So, I'm using this board that is:

- 3.3 Volt powered, so no mess with voltage converter in i2c lines
- resistor divider for 3 cells lipos voltage monitor
- "plug in" for powered current module (like hall effect current modules)
- possibility of adding a precision voltage reference (for better current / voltage measurements)
- Integrated i2c baro,
- port for external baro / i2c sensors... (for TKE variometers or other sensors).

The board has been flight tested from me...

Obviously there is lot of room for improvement (better layout, better routing, smaller etc), but this is... working.

Thanks to all you guy working on openXsensor.

Github repo of the board: https://github.com/sfabris/sensorboard.git
Picure of the board: Image

mstrens
Posts: 1435
Joined: Fri Dec 27, 2013 7:49 pm
Country: -

Re: My "Sensor Board" for OpenXsensor

Post by mstrens »

Great,
It is a nice board. It makes the full device much smaller than with the promini and separated board.
If you make your own board, it could make sense that I add support for bmp280 sensor to oXs. Those sensors seems cheaper than MS5611 and I read positive advices about their precision.
nigelsheffield
Posts: 308
Joined: Fri Nov 08, 2013 9:56 pm
Country: -

Re: My "Sensor Board" for OpenXsensor

Post by nigelsheffield »

Good idea. Really neatens everything up.
Is there somewhere that would make and populate the board cheaply?
Are you intending selling them?
Rough idea of prices?
Is there the possibility of adding more sensors later if needed?

I thought the bmp280 sensor was not as good as the 5611? If it is good enough for a vario then yes its a LOT cheaper which is better!!

I ws thingking of the bmp180 when I said it was not as good as ms5611, but bmp180 is super cheap £1 on eBay!
Last edited by nigelsheffield on Sat Feb 14, 2015 10:46 am, edited 1 time in total.
mstrens
Posts: 1435
Joined: Fri Dec 27, 2013 7:49 pm
Country: -

Re: My "Sensor Board" for OpenXsensor

Post by mstrens »

I just read once on this forum that bmp280 is a good sensor ( not to much noise) and that it was smaller than MS5611.
Here the link:
viewtopic.php?f=86&t=6080&p=91298&hilit=bmp280#p91298
If someone has more experience with bmp280, please add comments here.
nigelsheffield
Posts: 308
Joined: Fri Nov 08, 2013 9:56 pm
Country: -

Re: My "Sensor Board" for OpenXsensor

Post by nigelsheffield »

Sorry I edited my post, I was thinking of the bmp180.

User avatar
MikeB
9x Developer
Posts: 17990
Joined: Tue Dec 27, 2011 1:24 pm
Country: -
Location: Poole, Dorset, UK

Re: My "Sensor Board" for OpenXsensor

Post by MikeB »

This is, of course, a very good idea. Since it is based on using an Arduino it is very easy for users to update the firmware as well.

I just wonder, is it worth considering a larger (/faster) processor? An ATMEGA644A (44 pins) would give more flash, more RAM and a second USART, and can still run up to 20MHz from +5V.

The addition of hardware support for the SPort connection would also be useful, particularly if we have a second USART.

More difficult, due to the different flashing requirements, would be to use an XMEGA device. These only operate from 3.3V, but do allow operation upto 32MHz.

The ATMEGA644A solution would also be a closer software match.

A third solution would be to consider an ARM processor (STM?).

Mike.
erskyTx/er9x developer
The difficult we do immediately,
The impossible takes a little longer!
User avatar
jhsa
Posts: 19480
Joined: Tue Dec 27, 2011 5:13 pm
Country: Germany

Re: My "Sensor Board" for OpenXsensor

Post by jhsa »

But then most people wouldn't be able to diy their sensors anymore.. they would have to buy the sensor ready..
What about the teensy boards?

https://www.pjrc.com/teensy/teensy31.html

João

EDIT: Just checked, they are still too expensive.. :(
In my opinion, the very cheap arduino (2 or 3 dollars) is still the best approach.. :(
My er9x/Ersky9x/eepskye Video Tutorials
https://www.youtube.com/playlist?list=PL5uJhoD7sAKidZmkhMpYpp_qcuIqJXhb9

Donate to Er9x/Ersky9x:
https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=YHX43JR3J7XGW
nigelsheffield
Posts: 308
Joined: Fri Nov 08, 2013 9:56 pm
Country: -

Re: My "Sensor Board" for OpenXsensor

Post by nigelsheffield »

The arduino board is still going to be more flexible for adding sensors etc later but this is a good compact solution for tighter fuses and less weight, I was thinking about adding the cells voltage monitoring to mine but mounting resistors in a neat way is awkward, this solves the issue.
Can I ask, is the accuracy of monitoring a 3 cell lipo voltage using this sensor more or less accurate then doing it through the ad input in the RX ? Up till now I have stuck with d series simply because of the ad inputs, but now I am thinking I might as well start using the x series with s.bus.
sfabris
Posts: 8
Joined: Sat Jan 04, 2014 12:28 am
Country: Italy
Location: Vicenza

Re: My "Sensor Board" for OpenXsensor

Post by sfabris »

nigelsheffield wrote:Good idea. Really neatens everything up.
Is there somewhere that would make and populate the board cheaply?
Are you intending selling them?
Rough idea of prices?
This is just an hobby project, I'm going to make a few boards for my friends.
Is it also pretty simple to assemble and solder, and could be a "first smd board" for people.

About cost... I don't know... I think a few euro's for all the board pcb and components included, plus baro sensors, which is the most expensive parts...
I ws thinking of the bmp180 when I said it was not as good as ms5611, but bmp180 is super cheap £1 on eBay!
Be careful with ebay sensor... Most are out of spec parts. If you want a reliable sensor, buy it from primary distributors / resellers.
sfabris
Posts: 8
Joined: Sat Jan 04, 2014 12:28 am
Country: Italy
Location: Vicenza

Re: My "Sensor Board" for OpenXsensor

Post by sfabris »

nigelsheffield wrote: Can I ask, is the accuracy of monitoring a 3 cell lipo voltage using this sensor more or less accurate then doing it through the ad input in the RX ? Up till now I have stuck with d series simply because of the ad inputs, but now I am thinking I might as well start using the x series with s.bus.
Accuracy depends on calibration... In the board you can put a precision voltage reference so you can have the best reading out of the 10 bit arduino adc. But I usually calibrate openXsensor a little "on the safe side", few 10's of millivolt less than multimeter reading.

In my opinion, single cell voltage is the most accurate way to have a true battery status feedback: you can have a slightly unbalanced battery, and if you want to "save" it it's better to stop when the lowest cell voltage is approaching dangerous levels.
nigelsheffield
Posts: 308
Joined: Fri Nov 08, 2013 9:56 pm
Country: -

Re: My "Sensor Board" for OpenXsensor

Post by nigelsheffield »

OK, where do you recomend getting the sensors from?
I am in UK and I just built my first openxvario with eBay parts, tested only on ground so far but seems ok. So I ordered another set of parts.
sfabris
Posts: 8
Joined: Sat Jan 04, 2014 12:28 am
Country: Italy
Location: Vicenza

Re: My "Sensor Board" for OpenXsensor

Post by sfabris »

MikeB wrote:This is, of course, a very good idea. Since it is based on using an Arduino it is very easy for users to update the firmware as well.

I just wonder, is it worth considering a larger (/faster) processor? An ATMEGA644A (44 pins) would give more flash, more RAM and a second USART, and can still run up to 20MHz from +5V.

The addition of hardware support for the SPort connection would also be useful, particularly if we have a second USART.

More difficult, due to the different flashing requirements, would be to use an XMEGA device. These only operate from 3.3V, but do allow operation upto 32MHz.

The ATMEGA644A solution would also be a closer software match.

A third solution would be to consider an ARM processor (STM?).

Mike.
Well... I tried to make the board as small as possible. 44 pins cpu are bigger.. Also OpenXsenso is running well on atmega328p, so bigger / faster processor would be a waste of resources...

Next revision will be a 4 layers boards, so more compact than now. Probably with a four cell battery connector.
nigelsheffield
Posts: 308
Joined: Fri Nov 08, 2013 9:56 pm
Country: -

Re: My "Sensor Board" for OpenXsensor

Post by nigelsheffield »

Sorry, perhaps I should have said resolution with regards to volts measuring, is the 10 bit resolution better or worse then the frsky RX resolution?
User avatar
MikeB
9x Developer
Posts: 17990
Joined: Tue Dec 27, 2011 1:24 pm
Country: -
Location: Poole, Dorset, UK

Re: My "Sensor Board" for OpenXsensor

Post by MikeB »

The A1/A2 inputs use 8-bits analog to digital so the 10-bits is better.

Mike.
erskyTx/er9x developer
The difficult we do immediately,
The impossible takes a little longer!
nigelsheffield
Posts: 308
Joined: Fri Nov 08, 2013 9:56 pm
Country: -

Re: My "Sensor Board" for OpenXsensor

Post by nigelsheffield »

Thanks mike, and with the a1 a2 we are limited to 3.3v Max where as with a 5v arduino I can go higher up to about 4.4v?
sfabris
Posts: 8
Joined: Sat Jan 04, 2014 12:28 am
Country: Italy
Location: Vicenza

Re: My "Sensor Board" for OpenXsensor

Post by sfabris »

nigelsheffield wrote:OK, where do you recomend getting the sensors from?
I am in UK and I just built my first openxvario with eBay parts, tested only on ground so far but seems ok. So I ordered another set of parts.
I've heard of people getting MS5611 which have around 20 meters drift when placed on a firm position. So, if you have find out a reliable seller on ebay, please share!

I bough five sensors on farnell since now... These are obviously ok, but price is prohibitive: http://it.farnell.com/measurement-speci ... ost=ms5611
mstrens
Posts: 1435
Joined: Fri Dec 27, 2013 7:49 pm
Country: -

Re: My "Sensor Board" for OpenXsensor

Post by mstrens »

do you really think that MS5611 sensor from ebay are different from farnell.
I expect that there is only one provider for such a device.
Drift is not necessary caused by a bad sensor. It can be that atmospheric pressure changes during the day at the same location.
Take also always care that those sensors are very ligth sensitive. So do not forget to protect them.
Still, I think that the main reason for the drift is temperature drift.
When the sensor is read very often (like in oXs) his internal temperature increases by several degrees (about 5) compare to the ambiant temperature.
Normally each sensor has calibration temperature parameters that oXs uses but I presume that those parameters are not always correct.
I expect adding some extra parameter to oXs in order to get a better temperature compensation.
I have to make some more tests about this.
nigelsheffield
Posts: 308
Joined: Fri Nov 08, 2013 9:56 pm
Country: -

Re: My "Sensor Board" for OpenXsensor

Post by nigelsheffield »

One of my frsky altimeters changes 20 ft in the first few minutes by then is stable so temperature is probably the cause, in my dlg it wonders about a bit but that I am sure is presure changes.
The ms5611 I got off eBay was the one mounted on a board ready for the arduino not tested fully yet but seems OK. Cost £5.70 posted. I just looked for the cheapest and bought that!
Seems if you want the same sensor but on its own you have to pay more?!?!?!?
nigelsheffield
Posts: 308
Joined: Fri Nov 08, 2013 9:56 pm
Country: -

Re: My "Sensor Board" for OpenXsensor

Post by nigelsheffield »

Mouser.com sell the bmp 280 for £2 but postage is £12 , free postage on orders over £50......
mstrens
Posts: 1435
Joined: Fri Dec 27, 2013 7:49 pm
Country: -

Re: My "Sensor Board" for OpenXsensor

Post by mstrens »

on www.aliexpress.com, you can e.g. get 5 bmp280 for about 11.5 €.
nigelsheffield
Posts: 308
Joined: Fri Nov 08, 2013 9:56 pm
Country: -

Re: My "Sensor Board" for OpenXsensor

Post by nigelsheffield »

Just been looking there myself , 10 for £12....
nigelsheffield
Posts: 308
Joined: Fri Nov 08, 2013 9:56 pm
Country: -

Re: My "Sensor Board" for OpenXsensor

Post by nigelsheffield »

http://www.ebay.ca/sch/accecity-ca/m.html

This was who I got the vario from BTW, worryingly he has nothing in his store right now!!?!?

Post Reply

Return to “OpenXVario - an open source vario supported by the open source firmwares!!”