White-LED driver backlights LCD and keypad

Interrupt-driven keyboard for MCS-51

First, using interrupts frees the microcontroller to perform other tasks or to switch into an idling or power-down mode while awaiting the next key closure. Second, using interrupts helps reduce electromagnetic interference produced by continuously scanning the keypad`s lines. Figure 1 shows an...

7-Segment & Keypad

As shown in the circuit, Two common-anode 7-segment LEDs are connected to P1 with 180 Ohms current limiting resistor. Each segment of two LED are tied in parallel to P1.

Low-power keypad

The circuit in Figure 1 is a keypad interface that solves this problem by using an ultralow-power microcontroller. The circuit typically consumes 100 nA while awaiting a key press and consumes a maximum of only 2 µA if all keys are stuck or held down. An added bonus of the circuit is that it...

Multiplexing LED Drive and a 4x4 Keypad

Typically applications having LEDs and keypads also keep track of real-time, in order to synchronize certain related events. An Industrial Clock/Timer example has been used in this application note as a demonstration of these functions. The software overhead to keep track of real time is...

Implementing Wake-up on Key Stroke

The circuit, shown Figure 1, depicts an application with two keys. The PIC16C54 is normally in SLEEP mode consuming very little operating current. If either of the two keys is pressed, the PIC16C5X wakes up, scans the keys and turns on one or both of the LEDs.

Compatible Keyboard with COP8

This application note describes the implementation of an IBM MF2 compatible keyboard with National Semiconductor`s COP888CL or COP943C/COP880CL microcontrollers. Two different solutions have been developed. One solution, suitable for laptop/notebook keyboards is based on the COP888CL with...

Keyboard data-acquisition

The system is simple to operate. After you install it between the keyboard and the PC, the keyboard functions normally until you close the toggle switch, which puts the circuit into "acquire" mode. The system then bypasses the keyboard and "types" data into an Excel spreadsheet column at the rate...

Key-reading circuit saves I/O pins

First, consider some ways to effect key reading. Table 1 presents a comparison of four methods with references to circuit configurations (Figure 1, Figure 2, Figure 3 and Figure 4). As you can see, the best choice for reading many keys is to use the A/D converter that is inherent in many...