Programmable Digital Timer Switch Clock

This digital timer is designed for load control (start and stop) and has the ability to easy programming. The project is based on the PIC16F628A microcontroller. Turn off the device via the relay. The 110V digital timer switch allows you to program a time, turn the unit on and off. This feature enables for example at a certain time to enable any device, and then after a certain time to turn it off. The maximum time interval that can be set for the duration of the on-off device: 99 hours and 59 minutes. The project uses 16x2 LCD-display with 4 buttons for user interaction.

Schematic diagram of the timer is shown below. To control the 5V relay is used PN2222 transistor, which is controlled via pin RB3 microcontroller. Through ports RA2, RA3, RA4 and RB0, there is read state 4 timer controls. Description Timer control buttons will be lower. Standard 2 × 16 LCD-display is used to display the device status, menu and time. The display is involved in 4-bit mode and is therefore used only six I / O from the microcontroller PIC16F628A. A piezoelectric element is used to feed the audio signal at start or stop, and when you turn on or turn off the timer. The supply voltage of + 5V is provided by M / s LM7805 voltage regulator. Power schemes carried out by a 9V power supply.

On the concept of the conclusions of 15 and 16, the LCD display shows "in the air". These findings are used only on the LCD, which provides for the display light. If your LCD supports backlighting, connect these terminals to the power supply.

Now, see how it works. For example, you want to include any device through a timer relay, after 2 minutes. Then, after the 220V timer switch is switched on, it must remain on for the next 20 minutes. In this case, the off time is set to 00:02 and at 00:20 on time. When the timer starts, the unit will be turned on after 2 minutes, and will remain on for 20 minutes. After that, the device turns off.