Fig 1.7 GSM module with description 1. Power ON reset switch.
2. Sliding SIM holder.
3. Network, Power and Status indicator.
4. MIC and Speaker Socket.
5. Power supply 12V/2A
6. FRC Connector. 11
7. RS232 header.
7. DC to DC Converter (29302WU IC).
8. ESD Protection enabled.
9. SIM900A stack on header.
10. Stub antenna with SMA connector.
11. General GPIO SIM90
1. Features:
• Dual-Band GSM/GPRS 900/ 1800 MHz
• RS232 interface for direct communication with computer or MCU kit
• Configurable baud rate
• Power controlled using 29302WU IC.
• ESD Compliance.
• Enable with MIC and Speaker socket.
• With slid in SIM card tray.
• With Stub antenna and SMA connector
• Input Voltage: 12V DC.
• High quality PCB FR4 Grade with FPT Certified.
2. Applications:
• Industrial automation.
•…show more content… How it works:
First test whether any key is pressed down. Connect power to rows, so they are High level. Then set all the rows Y1-Y4 as Low and then detect the status of the columns. Any column of Low indicates there is key pressing and that the key is among the 4 keys of the column. If all columns are High, it means no key is pressed down.
Next, locate the key. Since the column in which the pressed key lies is identified, knowing the line would finalize the testing. Thus, set the rows as Low in turns until any is unveiled accordingly – other rows will still be High.
Now the row can be identified. Detect the status of each column in turns. The column tested Low is the one intersecting with the line – their cross point is just the key pressed.
The schematic diagram:
