After reading about Michaels tips (http://finch.am/projects/arduinogsm/) I decided to try using the same Gprs modem on the mbed. I thought it would be easy, because the mbed has it's own uart and the modem takes direct AT commands (after hacking it a bit).
After some soldering (and desoldering) I can talk AT commands to the modem using the mbed, but I can't get it to send SMS messages. In fact, the real problem seems to be getting the modem to register the network. After a lot of trying I found out that the AT+CREG? command always reports 0,2 which means it hasn't registered in any network (but is searching without ever finding any available network).
The sim card is ok, because it works on a cell phone and the modem also reports it's ok (AT+CPIN?). The cheap modem is very poorly documented without any mention of the three leds on it (green, yellow, red). The red must be power, because it always lights when the modem is powered on. The green indicates traffic, because it blinks when inputting AT commands.
I now have come to believe my poor electrician skills are the reason again, because when powering on the modem keeping the mbed in reset mode (button pushed) the modem starts flickering it's green led after a short while. I believe it's registering (or trying to) at that time. But when powering on the modem without keeping the mbed at reset it doesn't do the registering (green led flickering thing). However, querying AT+CREG? gives 0,2 regardless of how I power on the modem.
Edit: I've also checked the signal strength (AT+CSQ) which gives about 20, which should be good enough.
Is the wiring somehow messing up the modem so it can't register or what? I'm getting out of ideas to try. I noticed the modem doesn't answer to AT commands at all if the mbed's (who is executing the AT commands all the time) ground pin isn't connected to the modem's ground pin (ie. when powering the mbed from the pc usb cable)
Below is a state of the art schematic of my wiring. As you can see, no other components is used, just the modem and the mbed.
After reading about Michaels tips (http://finch.am/projects/arduinogsm/) I decided to try using the same Gprs modem on the mbed. I thought it would be easy, because the mbed has it's own uart and the modem takes direct AT commands (after hacking it a bit).
After some soldering (and desoldering) I can talk AT commands to the modem using the mbed, but I can't get it to send SMS messages. In fact, the real problem seems to be getting the modem to register the network. After a lot of trying I found out that the AT+CREG? command always reports 0,2 which means it hasn't registered in any network (but is searching without ever finding any available network).
The sim card is ok, because it works on a cell phone and the modem also reports it's ok (AT+CPIN?). The cheap modem is very poorly documented without any mention of the three leds on it (green, yellow, red). The red must be power, because it always lights when the modem is powered on. The green indicates traffic, because it blinks when inputting AT commands.
I now have come to believe my poor electrician skills are the reason again, because when powering on the modem keeping the mbed in reset mode (button pushed) the modem starts flickering it's green led after a short while. I believe it's registering (or trying to) at that time. But when powering on the modem without keeping the mbed at reset it doesn't do the registering (green led flickering thing). However, querying AT+CREG? gives 0,2 regardless of how I power on the modem.
Edit: I've also checked the signal strength (AT+CSQ) which gives about 20, which should be good enough.
Is the wiring somehow messing up the modem so it can't register or what? I'm getting out of ideas to try. I noticed the modem doesn't answer to AT commands at all if the mbed's (who is executing the AT commands all the time) ground pin isn't connected to the modem's ground pin (ie. when powering the mbed from the pc usb cable)
Below is a state of the art schematic of my wiring. As you can see, no other components is used, just the modem and the mbed.