On the project that we are currently developing, a SIM800L module is used.
Our device is only programmed to send an SMS when it gets a 5V digital pulse to microprocessor’s input (Arduino Nano).
The issue is about sending first SMS.
In intensive use, SIM module can send SMS for every single pulse applied to Arduino’s input but when it is set aside and after a while pulses applied, the first pulse is missing and no SMS sending.
For instance, if I set the device aside and after 1 hour if I apply 5 pulses, SIM module sends 4 SMSs (first one is missing sometimes).
So SIM module working as like its in sleep mode whether there is no AT command has been uploaded to set it in sleep mode. But sometimes first pulse in a daily usage is missing.
*Note: a1000uF capacitor has been soldered to Vcc and GND of SIM module but the problem still continues. Sometimes it does send the first SMS in a row of pulses but sometimes not.