GPS Tracker update

Success! More or less, anyway.

Using the nxpUSBlib (having made a few modifications – I'll do a post on that soon) I've managed to get USB CDC working and I got the GSM initialization and SMS receiving working.

At the moment, on receiving an SMS, the system will reply to the sender with the current GPS status regardless of the contents of the SMS.

(The GPS has no fix because it is on my workbench with no satellites in view.)

Power supply considerations

But: I need to do some careful design of the power supply. The GSM module is extremely power hungry. Especially when registering on the network or doing any other network related tasks – like sending or receiving SMSes. And the battery I'm currently using can not supply enough power for both the GSM module and (through a linear 3.3 V voltage regulator) the MCU and GPS module.

So I'll have to get a beefier battery (this 2000 mAh one) or this 6000 mAh one) and also add a low ESR capacitor (as recommended in the GSM module datasheet).
And I'll also add P-channel MOSFETs as high-side switches for the GSM and GPS modules in order to be able to switch power on and off to these modules.
At the moment I run the prototype off two separate power supplies: the 3.7 V LiPo battery directly connected to the GSM module and a 9 V battery supplying the MCU and GPS module through a 3.3 V LDO voltage regulator.

3 comments on "GPS Tracker update"
Xyrone Royd says:

Hi Sir,

Im glad that I saw this from your website though i have some question. I am currently having a simple project, just to send and receive sms using LPC1114 and GSM Module.

I tried sending sms command to the gsm module using the PC and I'm successful with it. The problem only occurs if I will send from LPC1114 to gsm module. It seems that my GSM module is not responding at all. By the way, i used rs232 converter to communicate my gsm module from lpc1114.

The gsm module instruction manual have this procedure for sending sms when using a PC through rs232
1. Send "AT+CMGF=1" then press "Enter". Wait for gsm module response "ok"
2. Send "AT+CMGS=********" and press "Enter". Wait for gsm module response ">"
3. Type the message. Then press "CTRL+Z".

Can you help me by providing some sample code for LPC1114 to do this task? I have my code already but it's not working. Hope you can help. Please pm me so that I can send you my codes.

theodore says:

What about the test results.
Powering the gsm straight form the battery works fine?

Jens Willy Johannsen says:

I'm using the 2000 mAh battery and a capacitor. And then it works fine. I did have problems powering the GSM module until I added the capacitor.

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