DEBOUNCE CIRCUIT
In electronics, two metal components tend to bounce or create multiple signals when they are in contact with each other — like when you push a button — before they get to a stable state. You want a single contact to be recorded, but the microcontroller records this as if you pressed the button many times.
So debouncing is, as the name states, the removal of bounces or spikes of low and high voltages. Graphically speaking, you want a clean line, not spikes. A debounce circuit makes sure that there are no voltage changes on the output. Thanks to it, one button press is recorded as such.
INTERRUPT SERVICE ROUTINE
All four Schmitt-trigger outputs are connected to input pins of the logic OR gate 74HC32, whose output is directly connected to the INT pin on mikroBUS. This pin is used to signalize an interrupt to the MCU any time a button is pressed.
In this way, the MCU software can be implemented as a simple polling routine, without any delays programmed in the code (like it would be necessary if there wasn't a hardware debouncing circuit present).
Thanks to the INT pin you can easily program a common interrupt service routine, in order to detect when a button is pressed (the state of the button changes from low to high logic level).
SPECIFICATIONS
| Type | Pushbutton/Switches |
| Applications | Human machine interface applications |
| On-board modules | 74HC32 quad 2-input OR gate from NXP and the SN74HC14 Hex Schmitt-Trigger Inverter from Texas Instruments |
| Key Features | 74HC32 quad 2-input OR gate, SN74HC14 Hex Schmitt-Trigger Inverte |
| Interface | GPIO |
| Compatibility | mikroBUS |
| Click board size | M (42.9 x 25.4 mm) |
| Input Voltage | 3.3V or 5V |
ADDITIONAL INFORMATION
- J2 is the interrupt enable pin (by default it is in the enable status).
- J1 is the power selection pin.
PINOUT DIAGRAM
This table shows how the pinout on 2x2 Key click corresponds to the pinout on the mikroBUS™ socket (the latter shown in the two middle columns).
| Notes | Pin | Pin | Notes | ||||
|---|---|---|---|---|---|---|---|
| When button T1 is pressed the pin is active | T1-OUT | 1 | AN | PWM | 16 | T4-OUT | When button T4 is pressed the pin is active |
| When button T2 is pressed the pin is active | T2-OUT | 2 | RST | INT | 15 | TINT | Interrupt pin that notifies the MCU that a button is pressed |
| When button T3 is pressed the pin is active | T3-OUT | 3 | CS | TX | 14 | NC | |
| NC | 4 | SCK | RX | 13 | NC | ||
| NC | 5 | MISO | SCL | 12 | NC | ||
| NC | 6 | MOSI | SDA | 11 | NC | ||
| Power supply | +3.3V | 7 | 3.3V | 5V | 10 | +5V | Power supply |
| Ground | GND | 8 | GND | GND | 9 | GND | Ground |