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Topic: Understanding the capabilities of MKRGSM1400  (Read 1 time) previous topic - next topic


My upcoming project, a remote alarm system, in the event that the unit gets an input from a switch, followed by an input from a motion sensor, in that order, the unit will need to send an SMS message alerting me that someone is where they are not supposed to be. Although if I am there I need to send an SMS message to the unit to tell it to disarm (ignore the inputs), and the opposite when I leave. 

If I am correct, I will need to have a SIM Card from someone like Twilio, Ting, or someone else, in order for me to send and receive a text message, because the Arduino SIM only talks to the Arduino IOT Cloud?

I understand that the unit will run exclusively from the 3.7V LiPo battery, which is what I prefer, assuming that I am correct? Is there any issues with going multiple cells with the LiPo batteries? I was debating back and forth between 4-8 18650 Batteries in parallel (14Ah - 28Ah) or just one 1165114 (10Ah). Is there any advantage or disadvantage to either? The 18650 chargers are easy to find and cheap where as the other charger is a little harder to find. I am after the larger Ah so we can go a few weeks between changing the batteries out.

Sense there will be a couple of these units (family with the same scenario as me), I was planning on using something like the MKR SD Proto Shield so I can read a text file on the SD card that contains the contact phone numbers and the specifics related to utilizing the SMS service that would vary between each unit. Since I have only spent the last 6 or so hours and haven't come across it yet, Is there any issues with utilizing the SD Shield with the 1400? That and is there any issues with the SD Shield because the unit will be running exclusively on the batteries?
I am only planning on reading from the SD Card at startup (void setup()).


Nov 29, 2020, 07:26 pm Last Edit: Dec 01, 2020, 10:37 am by intstarep
You can use any SIM card from a provider of your choice with a data plan (MKR1400 is only 2G + 3G).
With the MQTT protocol you can communicate with every broker (i use my own, a Mosquitto runing on a linux server)
You don't need the battery unless you have a old verison of the MKR1400. If you have an old model you have to replace a resistor and bridge a fuse. The resistor is a small smd part which is difficult to solder.
The proto shield is a good idea, it protects the board from voltage accidents while experimenting.
The MKR MultiShield ( https://mkrshield.com/ ) could be the right shield for you if you plan to do it serious.
It comes with display, Loudspeaker, TTL Level Shifter, superior voltage in handling (Micro USB and 5 to 35 V in), SD Card Reader, 16 aditional digital GPIO and a lot more


Part of what I am not understanding is everyone is saying "with a data plan". I am only planning on doing SMS messages to and from, why do I need a data plan? I am thinking I only need a minimal phone service plan, am I correct?


You're right. You won't need a data plan only for sms. I misunderstood you because you were writing about the Arduino IOT cloud.
One tough about your question about the 3.7 Lipo: This battery is controlled and charged from the internal controller on the MKR, controlled internally trough I2C. I don't think it's a good idea to attach another charger to this battery. Since the internal charger is for low capacity i guess your idea to enhance the capacity causes problems.
Why don't use the regular Micro USB of the board to power the board with a powerbank? 
I use a power bank from Voltaic. These devies have Chargetrough and Always On Technology. Especially the Always On thing is important because the Arduino is consuming so little power that a regular powerbank "thinks" the device is fully charged (normally a mobile phone) and cut the power completely.


In this case the unit will never be charging the batteries, except maybe occasionally during test / debugging. I thought about using a 5V USB Battery pack, but considering the other family members, the last thing I need is them saying that the battery is dead after a couple of days. This way they can have a spare set of batteries at home, charging with a charger and a set powering the unit.

The only other thing that I was wondering is there any internals that can be accessed to see what the battery voltage is or will I need to tie a jumper to the Analog Input and monitor it that way? Along these lines what is the lowest battery voltage that this will take prior to the unit stops functioning?

ps Thanks for your feedback instarep!


I do not understand. The LIPO has 3.7 V and can't be charged with a regular houshold battery charger because the AA AAA normaly used are 1.5 V. I can't see any reason to use this for powering the board.

A USB Powerback to power the arduino is cheap with lots of capacity and can be charged with every USB loader.
BUT : A 'always on' powerpack like to build on Voltaic is necessary otherwise the powerpack will cut the current after a while.

Whatsoever, the voltage of the internal 3.7 v lipo battery is readable with the following function:

int Batt_int = analogRead(ADC_BATTERY);
    // Convert the analog reading (which goes from 0 - 1023) to a voltage (0 - 4.3V):
float Batt_int_v = Batt_int * (4.3 / 1023.0);



Dec 20, 2020, 11:09 pm Last Edit: Dec 20, 2020, 11:14 pm by lavignema
I've put a precision DVM on the battery test points and compared it to the results of the calculations from analogRead(ADC_BATTERY) / 1023.0 * 4.3). I found them to be off by about 3% on mine. If you really are concerned with the battery power accuracy then measure the actual voltage and adjust your constant in the formula separately for each unit you make. Also consider the MKR MEM Shield instead of the MKR SD Proto Shield. Having the extra flash memory is handy and lets you read lots of stuff from the SD into memory not located on the MKR GSM 1400. Likewise if you need to construct lots of text messages in a library then this will be the way to go. Read them into the memory chip on the shield at startup and access them as you would any array. Don't worry about the size of the battery bank as you will not be using the onboard charger chip. Install fully charged battery clip and take back the old ones for recharging on a suitable rig with enough capacity for the size of the battery bank you employ. Also you can use the free Autodesk Eagle program to alter the MKR MEM Shield and customize connections for your devices. I've used it to create a shield with sockets for each sensor to plug into thus insuring secure and reliable connections. The cost of having these boards made is very reasonable.

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