Sim900 Won't Find Networks

Question

I have a Sim900 from Sainsmart. I have a working serial connection from my Raspberry Pi to Sim900. I can write commands, receive responses, and even query data such as my phone number from the Sim Card. My Sim Card is an AT&T card. I cannot make Sim900 find a network and attempt to connect. Supposedly, it is supposed to do it on its own, but I have not seen that either. The only two things I can think of are that either the firmware is wrong, or the chip is not getting enough power. The firmware (from AT+CGMR) is Revision:1137B06SIM900M64_ST_ENHANCE. This appears to be the latest firmware that you can get from Simcom's Site. As for power, I am pretty sure the power is sufficient as I bought a charger usb cable and adapter in which the adapter that came with the cable promised to support 2 amps. I stripped the cable and gave it a 3 amp supply of power. The chip also doesn't randomly reset when I try connecting it. I can set settings that get lost on power loss, but they only disappear when I unplug the chip to reset the settings.

The below output is from my latest test to try to understand why I cannot send SMS.

----------------------------------------------------------------------------------------
Command: "b'AT\r\n\r\n'" Response: "AT


OK
"
----------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------
Command: "b'AT+CMEE=2\r\n'" Response: "AT+CMEE=2

OK
"
----------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------
Command: "b'AT+CFUN?\r\n'" Response: "AT+CFUN?

+CFUN: 1

OK
"
----------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------
Command: "b'AT+CREG=2\r\n'" Response: "AT+CREG=2

OK
"
----------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------
Command: "b'AT+CREG?\r\n'" Response: "AT+CREG?

+CREG: 2,0

OK
"
----------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------
Command: "b'AT+COPS?\r\n'" Response: "AT+COPS?

+COPS: 0

OK
"
----------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------
Command: "b'AT+QBAND?\r\n'" Response: "AT+QBAND?

ERROR
"
----------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------
Command: "b'AT+CSQ\r\n'" Response: "AT+CSQ

+CSQ: 20,0

OK
"
----------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------
Command: "b'AT+QENG?\r\n'" Response: "AT+QENG?

ERROR
"
----------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------
Command: "b'AT+CIMI\r\n'" Response: "AT+CIMI

310REDACTED

OK
"
----------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------
Command: "b'AT+CNUM\r\n'" Response: "AT+CNUM

+CNUM: "","1678REDACTED",129,7,4

OK
"
----------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------
Command: "b'AT+CMGF=1\r\n'" Response: "AT+CMGF=1

OK
"
----------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------
Command: "b'AT+CSCS=?\r\n'" Response: "AT+CSCS=?

+CSCS: ("IRA","GSM","UCS2","HEX","PCCP","PCDN","8859-1")

OK
"
----------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------
Command: "b'AT+CSCS="GSM"\r\n'" Response: "AT+CSCS="GSM"

OK
"
----------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------
Command: "b'AT+CREG?\r\n'" Response: "AT+CREG?

+CREG: 2,0

OK
"
----------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------
Command: "b'AT+CMGS="978REDACTED"\r'" Response: "AT+CMGS="978REDACTED"

> "
----------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------
Command: "b'Pi\x1a'" Response: "Pi
+CMS ERROR: operation not allowed
"
----------------------------------------------------------------------------------------

The Python3 script that generated this output is below:

import serial
import time
import binascii

ser = serial.Serial(port='/dev/serial0',baudrate=9600,timeout=1)

command = bytes("AT" + '\r\n', 'utf-8') + binascii.a2b_hex('0D0A')
ser.write(command)
rcv = ser.read(1000)
print("----------------------------------------------------------------------------------------")
print("Command: \"%s\" Response: \"%s\"" % (command, rcv.decode()))
print("----------------------------------------------------------------------------------------")
time.sleep(1)

command = bytes('AT+CMEE=2'+'\r\n', 'utf-8')
ser.write(command)
rcv = ser.read(1000)
print("----------------------------------------------------------------------------------------")
print("Command: \"%s\" Response: \"%s\"" % (command, rcv.decode()))
print("----------------------------------------------------------------------------------------")
time.sleep(1)

#ser.write(bytes("ATE0" + '\r\n', 'utf-8')) # Reverse it with ATE
#rcv = ser.read(1000)
#print(rcv)
#time.sleep(1)

command = bytes('AT+CFUN?'+'\r\n', 'utf-8')
ser.write(command)
rcv = ser.read(1000)
print("----------------------------------------------------------------------------------------")
print("Command: \"%s\" Response: \"%s\"" % (command, rcv.decode()))
print("----------------------------------------------------------------------------------------")
time.sleep(1)

command = bytes('AT+CREG=2'+'\r\n', 'utf-8') # What does 2 do?
ser.write(command)
rcv = ser.read(1000)
print("----------------------------------------------------------------------------------------")
print("Command: \"%s\" Response: \"%s\"" % (command, rcv.decode()))
print("----------------------------------------------------------------------------------------")
time.sleep(1)

command = bytes('AT+CREG?'+'\r\n', 'utf-8')
ser.write(command)
rcv = ser.read(1000)
print("----------------------------------------------------------------------------------------")
print("Command: \"%s\" Response: \"%s\"" % (command, rcv.decode()))
print("----------------------------------------------------------------------------------------")
time.sleep(1)

#command = bytes('AT+COPS=?'+'\r\n', 'utf-8')
#ser.write(command)
#rcv = ser.read(1000)
#print("----------------------------------------------------------------------------------------")
#print("Command: \"%s\" Response: \"%s\"" % (command, rcv.decode()))
#print("----------------------------------------------------------------------------------------")
#time.sleep(10)

command = bytes('AT+COPS?'+'\r\n', 'utf-8')
ser.write(command)
rcv = ser.read(1000)
print("----------------------------------------------------------------------------------------")
print("Command: \"%s\" Response: \"%s\"" % (command, rcv.decode()))
print("----------------------------------------------------------------------------------------")
time.sleep(1)

#ser.write(bytes('AT+COPS=0'+'\r\n', 'utf-8'))
#rcv = ser.read(1000)
#print("\"%s\"" % rcv.decode())
#time.sleep(1)

command = bytes('AT+QBAND?'+'\r\n', 'utf-8')
ser.write(command)
rcv = ser.read(1000)
print("----------------------------------------------------------------------------------------")
print("Command: \"%s\" Response: \"%s\"" % (command, rcv.decode()))
print("----------------------------------------------------------------------------------------")
time.sleep(1)

command = bytes('AT+CSQ'+'\r\n', 'utf-8')
ser.write(command)
rcv = ser.read(1000)
print("----------------------------------------------------------------------------------------")
print("Command: \"%s\" Response: \"%s\"" % (command, rcv.decode()))
print("----------------------------------------------------------------------------------------")
time.sleep(1)

command = bytes('AT+QENG?'+'\r\n', 'utf-8')
ser.write(command)
rcv = ser.read(1000)
print("----------------------------------------------------------------------------------------")
print("Command: \"%s\" Response: \"%s\"" % (command, rcv.decode()))
print("----------------------------------------------------------------------------------------")
time.sleep(1)

command = bytes('AT+CIMI'+'\r\n', 'utf-8')
ser.write(command)
rcv = ser.read(1000)
print("----------------------------------------------------------------------------------------")
print("Command: \"%s\" Response: \"%s\"" % (command, rcv.decode()))
print("----------------------------------------------------------------------------------------")
time.sleep(1)

command = bytes('AT+CNUM'+'\r\n', 'utf-8')
ser.write(command)
rcv = ser.read(1000)
print("----------------------------------------------------------------------------------------")
print("Command: \"%s\" Response: \"%s\"" % (command, rcv.decode()))
print("----------------------------------------------------------------------------------------")
time.sleep(1)

#ser.write(bytes('AT+CNMI=2,1,0,0,0'+'\r\n', 'utf-8'))
#rcv = ser.read(1000)
#print(rcv)
#time.sleep(1)

# TEXTING

command = bytes('AT+CMGF=1'+'\r\n', 'utf-8') # Select Message format as Text mode 
ser.write(command) 
rcv = ser.read(1000)
print("----------------------------------------------------------------------------------------")
print("Command: \"%s\" Response: \"%s\"" % (command, rcv.decode()))
print("----------------------------------------------------------------------------------------")
time.sleep(1)

command = bytes('AT+CSCS=?'+'\r\n', 'utf-8') # Possible Value: GSM
ser.write(command) 
rcv = ser.read(1000)
print("----------------------------------------------------------------------------------------")
print("Command: \"%s\" Response: \"%s\"" % (command, rcv.decode()))
print("----------------------------------------------------------------------------------------")
time.sleep(1)

command = bytes('AT+CSCS="GSM"'+'\r\n', 'utf-8') # Possible Value: (8859-1/latin-1)
ser.write(command)
rcv = ser.read(1000)
print("----------------------------------------------------------------------------------------")
print("Command: \"%s\" Response: \"%s\"" % (command, rcv.decode()))
print("----------------------------------------------------------------------------------------")
time.sleep(1)

command = bytes('AT+CREG?'+'\r\n', 'utf-8')
ser.write(command)
rcv = ser.read(1000)
print("----------------------------------------------------------------------------------------")
print("Command: \"%s\" Response: \"%s\"" % (command, rcv.decode()))
print("----------------------------------------------------------------------------------------")
time.sleep(1)

command = bytes('AT+CMGS="978REDACTED"', 'utf-8') + binascii.a2b_hex('0D') # 0D is CR
ser.write(command)
rcv = ser.read(1000)
print("----------------------------------------------------------------------------------------")
print("Command: \"%s\" Response: \"%s\"" % (command, rcv.decode()))
print("----------------------------------------------------------------------------------------")
time.sleep(5)

command = bytes("Pi",'utf-8') + binascii.a2b_hex('1A')
ser.write(command)
rcv = ser.read(1000)
print("----------------------------------------------------------------------------------------")
print("Command: \"%s\" Response: \"%s\"" % (command, rcv.decode()))
print("----------------------------------------------------------------------------------------")
time.sleep(5)

#ser.write(binascii.a2b_hex('0D0A')) # 0D is CR
#rcv = ser.read(1000)
#print("\"%s\"" % rcv.decode())

Also, the same issue happens when running in minicom. This is not a Python specific issue. Although there is an issue with displaying data from the AT command "AT+COPS=?" in Python. However, the displaying bug is an issue for another day as I can still read it in minicom.

Edit: Clarify the question

Basically, I want to know why I cannot send SMS and how to fix it! I am sure it has to do with not registering on any network, but no network shows up to connect to when running "AT+COPS=?". Listing any potential reasons is appreciated. I can do things such as take a picture of my setup if I need to.

Edit: Provide some insight to "AT+COPS=?"

Using Minicom, I get the below result with "AT+COPS=?". I cannot test this command in Python 3 as it makes the feedback from itself and all other future commands empty, as in empty quotes (e.g. ""). It is a problem even when CMEE is enabled to provide verbose text. This gets reset when I reset the Python program.

AT+COPS=?
+COPS: (1,"Off Network","","310260"),,(0,1,4),(0,1,2)

OK

I get the above result every time I run the command, no matter what I set CREG to.

Links: Amazon Page Where I Bought Sim900

If we cannot figure out what is wrong with this by the 20th, then I will test with a different sim card. I should get my Project Fi sim from Google by that date and the post office be open by the following Monday, so I can see if it is having AT&T that's the issue. Given that, the SimCom page linked in the question for firmware says AT&T is a supported carrier. I guess we'll find out. — Alexis Evelyn, Jan 13 '18 at 14:58
You may want to ask this over on https://raspberrypi.stackexchange.com/. — larsks, Jan 13 '18 at 15:46
@larsks. I have thought about putting the question on RPi, but all the pi does is act as a terminal to control a completely separate chip. RPi wants software problems specific to the Pi, but I have no problems with controlling the chip, especially with Minicom. I am 90% sure that there is a software problem with the Sim900 though, and so it would be a great fit for StackOverflow. If it turns out it isn't a software problem, then I will ask this on a generic hardware site. — Alexis Evelyn, Jan 13 '18 at 16:06
No worries. I Just figured you would find more folks over there who had worked with this kind of hardware. — larsks, Jan 13 '18 at 16:28
No! No! No! You should [never, never, never, never, never, never, never, never, never, never, ever use time.sleep like that](https://stackoverflow.com/a/46064206/23118). You MUST **read** and **parse** the responses given back by the modem, otherwise you will [abort](https://stackoverflow.com/a/1389034/23118) the commands. — hlovdal, Jan 19 '18 at 21:37

score 1 · Accepted Answer · edited Jan 19 '18 at 21:29

It turns out there is nothing wrong with either my code or hardware. This is an issue with my network provider, AT&T. Now, I knew they got rid of 2G, but I didn't realize that meant calls and texts too. Because I forget calls and texts aren't on their own separate protocol. Since, I am typing this on my phone, I will just use screenshots to show what I mean.

This is a list of network submodes. My phone is usually on the top option with LTE data. My GSM chip uses the second option, obviously GSM. I may be able to hack together a slower LTE connection as I still support the bands that AT&T's LTE network provides. I would just have to see how feasible it is to hack the firmware.

Network Submode

This is what my network list for LTE looks like when scanning (essentially AT+COPS=?):

LTE Network List

This is the same output of what my GSM chip sees. This is with the GSM option. I cannot call anyone when selecting the off network option.

GSM Network List

Given this, I either need to find a carrier that supports GSM, hack together the firmware to support slow LTE, or chop off my arm and sell it on the black market for an expensive LTE chip.

All the AT commands should be LTE compatible (some of them have visible traces of that in the `` *access technology of the registered network* parameter). Of course the networks might be configured with different supports, but not supporting SMS messages seems wierd. — hlovdal, Jan 19 '18 at 21:36

Sim900 Won't Find Networks

1 Answers1