First test whether any key is pressed down. Connect power to rows, so they are High level. Then set all the rows R1-R2 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.
1 * 2 x 2 Matrix 4 Push Button Keyboard Module
₹30.00 ₹60.00
The 2×2 matrix keypad module usually is used as input in a project. It has 4 keys in total, which means the same input values. The module is a non-encoded matrix keypad consisting of 14 keys in parallel. The keys of each row and column are connected through the pins outside – pin R1-R2 as labeled beside control the rows, when L1-L2, the columns.
It consists of microswitch buttons. The module has four holes 3mm (M3) holes for mounting. The pin designations on each PCB are shown on each PCB. Two pins are thus used as an ‘x’ coordinate and the other 2 as a ‘y’ coordinate.
The module is already equipped with a soldered pin-headers (rotated 90 degrees)
Third eye glass for blind person with vibration motor, buzzer and led ready to use complete project kit || No assembly required 
Mini CNC Plotter Kit, 3D Printed Parts only 
LM358 OP-Amp (Dual Operational Amplifier) - (5 Pcs) AB0119 
