Microcontroller › Arduino › interfacing gsm sim900A modem with arduino uno › It might be due to Improper
February 14, 2016 at 9:09 am #13702
It might be due to Improper Baud Rate.(If you have changed default baud rate of modem from 9600 to other value using AT command) Make simple test program to check "OK" response from modem when you sent "AT" to it. If battery is not delievering enough current then also SIM900A fail to send message.