[General] Reliabilty of SIM900A for larger number of projects.

I would like to know if sim900A will be reliable for long run, since this module is going to be used for upcoming 30 projects for sending sensor data (current, voltage, temperature) to a ftp server and also it will be retrieving messages from other cellphones which will be used for setting credit (i.e. setting the expiry time which will then be compared for RTC's current time).

not evident to give you a response ...

what about your Software reliability ?
and environnement ?
what about the Power supply, EMC distubations... etc ..

The SIM900A could be enough reliable itself (MTBF,technical caracteristiques,firmware test,
but depend of the usage context .

i France ,we have a lot of devices coming fro RPC with the mark "CE" compliant ..
but this CE mark is not validate when using it in another context .
Device + Other hardware + Application software ..must be "CE" certified by doing many tests.

Thanks for your feedback.
The pcb with all the components has been fairly stable in our testing period of 1 months. But still I'm not comfortable with my microcontroller(Arduino Mega 2560) and software burnt in it. As for the power supply we are using a buck converter which converts 24V dc from solar panel to 12 v and then L7809 and L7805 to convert it into 5v which is distributed to all the components. The 12v from buck converter paired with BC547 to control the 3-Phase relay.
These meters will be deployed mostly in rural areas of Nepal.
I,m very confident about the PCB and the hardware(except μC and GSM) used but is there any way to certify the software and also we are ready for design changes since arduino(microcontroller) is not ideal for large scale deployment.

https://obrazki.elektroda.pl/3108353700_1512372495.jpg
https://obrazki.elektroda.pl/6246099800_1512372497.jpg
https://obrazki.elektroda.pl/4078096500_1512372519.jpg

Hi,

I assume there is no need to put the antenna through a hole, because the plastic case won´t reduce the RF significantely.

You are dealing with HF on the one side, but the wiring and the PCB layout is far away from beeing suitable for this HF.
--> use short wires, twisted where useful. Use common mode chokes on power supplies, use EMI/EMC filters at all PCB_IOs.
Use a solid GND plane on your PCB.
This all is to avoid the HF to reduce your system reliability.

****
What fauts do you expect? What faults can be tolerated? What faults must be avoided?

Example:
If you just want to to avoid that the system hangs continously in a way that a person needs to open the box to reset the device:
--> then use a hardware watchdog. It detects when the system hangs for a dedicated time and restarts the system automatically.

Klaus

Thanks for the advice.
You hit the target. We had hang issues but we partially solved it using the software reset but now as you have mentioned above I am sure now we certainly need watchdog timer.
Most importantly of all we are ready for design changes if Arduino is not suitable this kind of project and what are the necessary steps to pursue this changes.
Thanks once again.

hello,


Did you allready made some test with Ambiant temperature
-10°C or less or >30°C
RTC quartz can stop ..
or bad contact between modules inserted on inline support .
like RTC Board, ...
quality of support .. tulipe type ?

another point is humidity (condensation) into the Box ...when ambiant temperature change.

in NEPAL .. Altitude ?

I am sure there isn't any significant bad contacts between the modules.
We don't need exact real time from RTC, there is wider margin of error for this but what can be done to minimize this. The ambient temperature in Nepal is fairly stable in all seasons.
About the humidity inside the box, it is IP65 certified(Hansel box) although we have made some holes we have used silicon sealant to seal those holes.
The altitude of the sites that we are planning to install will be at the range of 100-200 meter.
Thanks!

About the humidity inside the box, it is IP65 certified(Hansel box) although we have made some holes we have used silicon sealant to seal those holes.

Click to expand...

Quite generally, this doesn't work. An IP65 enclosure is never gas-tight, it "breathes" along with atmospheric pressure variations. As a result, the enclosure inside approaches the outside humidity after a certain time.

A reliable method to keep the enclosure inside dry is a goretex membrane vent.