CODEWITHSUNDEEP
arduinogsm
RickJansen
RickJansen

Reputation: 1713

SIM808 GSM+GPS module sleep and power usage?

I'm using a SIM808 GSM+GPS module on a LoNet breakout board: http://www.seeedstudio.com/wiki/LoNet_-_GSM/GPRS/GPS_Breakout with an Adafruit Trinket Pro 3V, and everything works.

I've taken care to build in power save modes in my application. I can enable the SIM808 slow clock, so it can sleep with DTR=1, which I call "light sleep" mode. Also there is a "deep sleep" mode, where I set AT+CFUN=0 to further decrease functionality of the SIM808, and power usage. (During deep sleep the RF circuits are off, so no SMS reception..)

I've measured power consumption by measuring the voltage across a 1 ohm resistor in series with the battery.

During normal GSM operation 19-20 mA is used; with slow clock enabled also 19-20 mA, in deep sleep 18-19 mA.

Switching on GPS makes the board use 43-44 mA. I see no difference while acquiring the GPS fix, or when a fix is reached. The wiki page (above) says that continuous tracking takes 24 mA, but apparently that is on top of the 20 mA when just the GSM is used. Indeed 20+24 is 44 mA, the value I measure.

I'm quite disappointed that the sleep conditions don't seem to save any power!

Should I do things like remove the green power LED? The design drawing shows a 470 ohm R in series, so that could save ca 8 mA?

The board does have a battery charging circuit; could that be responsible for the 20 mA base current? When I power down the SIM808 only ca 0.02 mA is used, so I wonder if there is an external circuit responsible for the 20 mA base current. The SIM808 Hardware Docs spec a power consumption of around 1 mA only! - I wish!

Upvotes: 1

Views: 8535

Answers (1)

Surroot
Surroot

Reputation: 21

I had the same problem like you but on another board. As you can see at the top of the board below the right one of the two SMA connectors it says: "Active GPS Antenna". And thats the solution to the problem.

When I disconnected the GPS antenna the current dropped to ~670µA without LEDs and when slowclock (AT+CSCLK=1) was enabled, AT+CFUN=0 and DTR pin was high (eg. 3.3V).

So if you want to really make your SIM808 module low power you have to switch the active GPS antenna off with a PMOS.

This image shows the active GPS antenna circuit of my SIM808 Module.

EDIT:

Damn I don't know how to delete or edit a comment... And I can't post more than 2 links, please go to the next links by yourself:

This wiki page (wiki.seeedstudio.com/wiki/LoNet_-_GSM/GPRS/GPS_Breakout) of the LoNet states that: "GPS Antenna: this is an uFL GPS antenna connector. You can connect either passive or active GPS antenna to it. Active GPS antenna runs at 2.8V voltage."

And the schematic (wiki.seeedstudio.com/images/3/37/LoNet_808_Schematic.pdf) shows in the top right corner, that the GPS connector is prepared for an active antenna (the inductor in series with the current limiting resistor). So if you don't have an active antenna you maybe can just cut the trace between the inductor and the GPS connector.

I don't know what will happen when you are using a passive antenna, you have to try it yourself. Good luck!

Upvotes: 2

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