M590 chip is similar with SIM900, just haven't voice part...
First, I upload M590_Mega_serialmonitor.ino sketch and I send from phone a SMS to GPRS module:
I use this schematic for tests:
I upload M590_tronixstuff_sms_control_Arduino_v1m0.ino sketch and send #a1b0c1d0 text in SMS from phone:
(aprins = on, stins = off)and leds 1 & 3 are on, 2 & 4 are off:
I send #a0b1c0d1 SMS:
(aprins = on, stins = off)and leds 1 & 3 are off, 2 & 4 are on:
I send a new SMS, for all leds lit (all on):
and all led are lit.
I made a movie named SMS control 4 leds using M590 GPRS module and Arduino with sending sms from phone and received from M590 GPRS module, interpret datas and comand 4 leds:
NOTE: External power supply is +4,6V not 4,2V (power supply with voltmeter show less with 0,3-0,4V) !