LCD & Keypad drive

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...

RS-232C scans remote keypad

If you have no parallel ports available for this purpose, you could use a standard RS-232C port. With the method shown here, you need only some wire and a few passive components to connect a keypad with as many as 15 keys to the RS-232C port, at distances to 50 ft.

Keypad encoder

The MM74C922N combines all elements needed to scan detect, debounce, encode, store, and transmit contact closures in an X/Y switch matrix. The IC combines these functions in a way that makes it useful in stand-alone applications and as a bus-oriented system device. An internal RC oscillator (or...

4-Digit Alarm Keypad

The circuit is easy to use. When you press "E" - current through D2 & R9 switches Q5 on - and the transistor energizes the relay. The 12-volt output moves from the "off" to the "set" terminal - and the green LED lights. At the same time - R10 takes over the job of supplying base current to...

LCD & Keypad drive

No description available.

5-Digit Alarm Keypad

The circuit is easy to use. When you enter the first four digits of your security code - the relay energizes. The 12-volt output moves from the "off" to the "set" terminal - and the green LED lights. At the same time - R12 takes over the job of supplying base current to Q6. In effect - the relay...

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...

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...