Multi Stage Simple Programmable Timer Circuit - 16F628A

Electronic delay timers are devices which are able to count and produce different time delay intervals as per the external settings. The elapsing of the set time is mostly indicated through an audible alarm to alert the user. Timers play an important role in our everyday life, whether it’s your cell phone, wall clock, TV/DVD sets, computers they are present everywhere.

Usually an ordinary electronic timer is able to produce single-shot delay intervals and setting up its initializing point becomes inaccessible. The present simple programmable timer circuit design eliminates this drawback.

Simple Programmable Timer Circuit

This is a one of the simple circuit of programmable timer circuit. The time range of this timer is 1 second to 255 hours. The delay time can be change by dip switches. The whole circuit of programmable timer is build using cheap PIC16F628A microcontroller and few passive components.

Circuit Operation

After power applied, the START led will turn on and you need to configure the delay time, timer mode and repeat mode. The delay time of this circuit can change by using dip switches. Those dip switches are represent 8-bit binary number and that number use to set delay time. When the delay time over, RLY ON led will turn on.

Eg:
If you need to set delay time to 150 then, dip switch configuration is 10010110 (RB0-RB7).
1 = Off and 0 = On

When you pressed the START button, START led will begin to blink and you can observe timer status by that.

Time Mode

This circuit can operate in 3 different time modes (Seconds, Minutes and Hours). Those modes can select from MODE buttons.

1. If both PORTA.F6 and PORTA.F7 are low or high, then circuit is running in seconds’ mode (0 – 255 seconds)
2. If PORTA.F6 high and PORTA.F7 low, then the circuit is running in minutes’ mode (0 – 255 minutes)
3. If PORTA.F6 low and PORTA.F7 high, then the circuit is running in hours’ mode (0 – 255 hour)

Repeat Mode

If PORTA.F1 is low then repeat mode will turn on. The circuit running continuously and RLY ON led will turn on and off repeatedly.

To control heavy load, remove RLY ON led and connect 5v relay through NPN transistor. Then connect you device across the relay. Supply voltage for this circuit is 5v and use voltage regulator ic such as LM7805, if you use voltage above that.

Simple Programmable Timer
MikroC Code

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Programmable Digital Seven Segment Timer Circuit - 16F628

Seven Segment Timer

A timer is a specialized type of clock for measuring time intervals. By function, timers can be categorized to two main types. Those are Counts upwards and counts downward.

Timers originally designed to fulfill a need in industry for a means of keeping time on certain devices. Originally, these timers were mechanical devices and used clockwork mechanisms as a means of keeping a regular time. The invention of two electromechanical timer designs allowed for more precise time measurement. The first uses the principle of heat expansion to increase the temperature of a metal finger made of two different metals with differing rates of thermal expansion. As electric current flows through the metal, it begins to heat and one side expands more quickly than the other does, which in turn, moves the electrical contact away from an electrical switch contact. The second uses a small AC motor, which turns at a predetermined rate due to the application of an alternating current.

Finally, digital timers invented. Digital logic circuits are now so cheap that it has become a better investment to buy a digital timer than a mechanical or electromechanical timer. Individual timers implemented with single chip circuits.

This is a very simple adjustable digital timer circuit based on the PIC16F628A microcontroller and it can be programmed to schedule the on and off operation of an electrical appliance. This timer consists of three parts: power supply, control circuit and display. Working voltage of the circuit is 5v - 12v. It depends on the relay voltage. If you use 5v relay then you can omitted the LM7805 regulator IC and apply 5v directly. Otherwise, you have to use regulator IC and apply suitable voltage according to the relay voltage. The schematic is very simple and accurate of the circuit is very good. PIC use its internal oscillator.

Programmable Digital Timer Schematic

There are two versions of hex file are available. Those are "4dg_tmr_min.hex" and "4dg_tmr_hr.hex". The first file for the minute timer. It display minutes and seconds. Adjustable time is 1 second to 60 minutes. Other hex file for hourly timer and its adjustable time is 1 minute to 24 hours. This will display hours and minutes on the seven segments.

Configuration

If the time runs too fast or too slow, you can able to adjust the speed by changing the value of Eeprom address 0. Default value is 44 (0x2c). Typical value is 59 (0x3B). Maximum is 255 (0xFF). In repeat mode delay time before restart the timer, determine by value of Eeprom address 3. Default value is 10 (0x0A). Maximum is 255 (0xFF). See below picture for more details.

Eeprom Configuration

Operation of the timer

This circuit uses 5 push buttons to control the their functions.

• START/PAUSE: When the timer is on, the device is in pause condition even the switch was in closed position. Pressing this button, you can switch between the start and pause timer.
• FOR/BACKWARD: This allows you to select counter mode. Either upwards or count down.
• REPEAT: When the timer reaches 00:00, it starts again from previous value you set.
• LEFT/RIGHT: This allows you to change values on display. The selected digit is incremented by pressing those buttons and values on the display are stored to the Eeprom.

Now connect device you want to operate, through the relay. Set the desired time using left and right buttons and press start. When the timer reaches 00:00, relay will activate.

Programmable Digital Timer

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Seven Segment Up Counter and Timer Circuit - 16F628

Circuit diagram

The project shows what can be done with a micro and you can modify it to set an alarm at any count-value or set a limit such as 'count-to-60'. You can add a buzzer or relay or increase the display to 3 digits. You need to remember that each additional display will reduce the illumination of each digit as they are 'multiplexed (time-sharing)'. Full circuit diagram including programming socket.

The displays do not affect the 'In Circuit Programming' as they are not active when programming and do not load the outputs. Any 7-Segment displays will work in this circuit. You need to identify the pin-out of any display you use. (Common Anode displays can be used providing you invert the values in the display table. A PNP transistor will need to be used.)

Testing the circuit

Check the circuit by removing the chip and taking pins 6 and 18 to the 5v rail ad make sure segment 'A' illuminates. Do the same for all the other segments.The circuit diagram does not have any voltages marked on it as the circuit is DIGITAL.All the 'lines' or 'wires' or pins of a micro-controller will have rail voltage (5v) on them when they are HIGH and when you come to a resistor, the resistor will drop a certain voltage. The voltage it will drop will be the difference between rail voltage and the voltage developed across the component it is driving. If it is driving a LED, the LED will drop a characteristic voltage of between 1.7v and 3.6v, depending on the color. If the component is a transistor, the voltage developed between the base and emitter will be about 0.7v.

Use Micro C For Compile.

PIC16F628A Datasheet

pin-out

PIC16F84A Datasheet

pin-out

Counter (For 16F628A)
Counter/Timer (For 16F84A)
Proteus Files

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