Multifunctional locator

"This may be a long-term update project... Because it involves a lot of things, and I'm in my senior year of high school and I don't have much free time. I'll try my best to release a demo before the event ends."

Supplement: Since a more cost-effective solution was found, the SIM868 (￥50 single module) was changed to the A9G package (￥20 including two antennas), the cost was reduced by 40￥, and the entire document is being rewritten. . .

1. Design background

This weekend, I lost my campus card (rice card) and citizen card again (┙>∧<)┙へ┻┻

After going through extremely troublesome reissues, I wanted to make something to locate the card package.

2. Introduction

Use A9G+ESP07-S, support GSM/GPRS/GNSS/2.4ghz wifi

First use GPS/BDS/base station for rough positioning, then use 2.4ghz wifi to find the exact location

This project can be directly inserted into the card holder. After successful testing, it can be used in daily life and has practical value.

3. Knowledge points

(1) Learn the design ideas and methods of low-power products;

(2) Learn how to use the A9G module;

(4) Learn the size estimation of the final product;

(5) Learn to write simple programs with Arduino;

(6) Learn to use UART to communicate with SIM868;

(7) Learn to use TCP protocol to send data to the server;

(8) Learn simple server back-end construction;

(9) Learn simple processing of data sent from MCU;

(10) Learn simple front-end data display;

(11) Learn to use Lichuang EDA to design schematic diagrams and PCB diagrams;

(12) Learn the composition of PCB boards and factory production processes;

(13) Practice welding skills and master the use of multimeters, soldering irons and other tools;

4 How to use SIM868 module

There is no datasheet for A9G in the mall. You need to go to the official website of Anxinke to find it. The information is quite complete.

5 size design

The board was redrawn and the length was greatly reduced, so there is no need to consider whether it will fit in.

But this board has requirements for board thickness, and it can only be made with 0.8MM boards.

6 layout

Convert the schematic diagram to PCB and estimate the size of the lower border. It can be slightly larger for later adjustment.

First determine the positions of A9g and ESP07

Then adjust the position of the components according to each module of the schematic diagram, and then combine these modules

Finally started to pull the thread

6.1 Power supply

The power supply trace must pass through the filter capacitor, otherwise the filter capacitor will not be effective.

6.2 RF

GNSS and GPRS require an impedance of 50Ω. Since we can only use double-layer boards, we can only use 0.8MM thick boards with a line width of 46mil and the length should be as short as possible.

7. Welding

8. Debugging

Insert the sim card (note that China Telecom’s card seems to be unusable, unable to attach to the network and activate PDP, and prompts that network registration is refused. We have contacted Anxinke’s technical support, but there has been no reply)

It is recommended to use the mobile Internet of Things card, 10M per month for the year, and you can get it for three yuan~

Solder the battery and plug in the typec cable to charge to activate the battery protection chip

Then burn the test code to esp07

#include <SoftwareSerial.h>

SoftwareSerial test(14, 12, false);

void setup() {
    Serial.begin(115200);
    test.begin(115200);
}

void loop() {
    while (test.available() > 0) {
        Serial.write(test.read());
    }
    while (Serial.available() > 0) {
        test.write(Serial.read());
    }
}

Plug in the GPRS and GPS antennas

(Note that if it is a GPS active antenna, it is best not to plug it in while it is plugged in. It is easy to short-circuit and L2 is easy to smoke/burn)

Open the serial port and restart the A9G. You can see that the initialization is normal and the time sent by the base station is returned.

At the same time, LED2 on the board changes to slow flashing

At this time, you can use the GPRS base station for positioning and directly return the latitude and longitude.

Turn on the GPS, LED1 on the board flashes quickly, and the serial port returns GPS information (there is a problem with the data because there is no GPS signal indoors)

"To be continued..."