The GSM frequencies for the AT&T network in USA are 850 MHz and 900 MHz. The power consumption of the Telit GM862 is determined by the strength of the signal of the closest cellular tower. If you’re in the he 850 MHz region, then you must prepare for peaks of 2A; the 900 MHz region are more efficient and only peaks of 1A need be anticipated. The peak current typically happens during network initialization, i.e., when you turn the module on and it attempts to register on the AT&T network. You can use various AT commands such as AT#MONI and AT+CSQ to find out which frequency region you fall under.
During normal operation in well served cellular regions, the peak current consumption seems to be a lot more reasonable (but still quite high) — around 150mA.
August 11, 2009 at 2:34 pm |
AT&T of North America does not use the 900MHz cellular band.
850MHz and 1900MHz yes.
900 is used in Europe & Australia.
August 23, 2009 at 3:27 am |
SJ, I have been checking my GM862-GPS RS232 Eval Board’s current usage in its various modes. I am directly connected via TTL serial but the converter chip is probably still using some power and it has a power led and status led. If I put the GPS power supply in power save mode 2, then under the registration status 1, RSSI approx. -100, channel 747, my current averages 35-40 mA. When the GPS awakes to obtain a new fix, it uses 75mA total. When sending/receiving a SMS while the GPS is asleep, it shows about 65-75mA total. The only time I see 150mA is during the network registration process. I played a bit with the AT+CFUN command. Setting it to 4 (disable TX & RX) doesn’t seem to do any good, current usage sits at a steady 45mA, higher than when its registered and just idling.
August 23, 2009 at 3:40 am |
Great info Matt. Thank you. Now that I look back at my post, I see that I failed to mentioned that I only see the 150mA during registration as you’ve pointed out. In our design, we put the Telit under full control of Arduino Mini Pro. The modem is sleep most of the time, we wake it up for out-bound communication and at that point also handle any incoming SMSs, and then turn it completely off.
One problem is that it takes about 60 seconds to start it, register with the network, and send an SMS or two. The main reason for this huge amount of time is in all of delays that I had to put in between Serial.print statements. Without the delays, I found the reliability was compromised. This cannot be right. Do you also use a lot of arbitrary delays in between Serial.prints?
December 31, 2011 at 8:14 pm |
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