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

Read More

Digital LCD Speedometer and Odometer Circuit - 16F628

Speedometer

In my previous post, I explained how to build a simple speedometer circuit using a micro-controller and seven segments. Read it from here. This is a further development of that circuit. This circuit indicates both speed and distance.

A speedometer or a speed meter is an instrument that measures and displays the instantaneous speed of a vehicle. An odometer or odograph is an instrument that indicates distance traveled by a vehicle.

Speedometer + Odometer Circuit

For this circuit I used PIC16F628A micro-controller and 16x2 LCD. You can able to see speed in first line and distance in second line on the LCD. Distance will update every 100 meters and speed updates every one second. Value of distance writes to Eeprom in every 1 km. I also added a button to this circuit. The purpose is, reset the distance to zero.

Same as the Speedometer Circuit, micro-controller count the signals received to RA4 pin and then calculate speed and distance, then display information on LCD. 8 MHz resonator is use to generate clock signals. However, you can always use crystal for it and make sure to add 22pf ceramic capacitors if you use crystal oscillator.

Measure the radius of the wheel and enter it to Eeprom address 0x00. Default value for radius is 30cm (0x1E). I used two magnets to operate reed switch. Please refer my previous post for more details and circuit connection.

Maximum speed is 999 kmh
Maximum distance is 9999 km
Supply voltage is 5v

Speedo + Odometer

Read More

Digital Seven Segment Speedometer Circuit - 16F628

Speedometer

How Electronic Speedometers Work

In Electronic speedometer, small magnets attached to the vehicle's rotating drive shaft sweep past tiny magnetic sensors (either reed switches or Hall-effect sensors) positioned nearby. Each time the magnets pass the sensors, they generate a brief pulse of electric current. An electronic circuit counts how quickly the pulses arrive and converts this into a speed, displayed electronically on the display. Since the circuit is measuring the number of wheel rotations, it can also keep a count of how far you have traveled, doubling-up as an odometer (distance-measuring meter). Electronic speedometers can also display speeds with analog pointers and dials, just like traditional eddy-current speedos: in that case, the electronic circuit drives a highly controllable electric motor (called a stepper motor) that rotates the pointer through an appropriate angle. Electronic speedometers are more reliable and compact than mechanical ones and the motion sensors can be any distance from the display that shows you your speed, making them suitable for any kind of vehicle!

1. A magnet connected to one of the wheels rotates at high speed.

2. Every time it makes one complete revolution, it passes a magnetic sensor and the field from the magnet triggers the sensor.

3. A circuit translates them into your instantaneous speed and distance traveled.

4. A digital display displaying the speed and distance.


Here I will show you how to build simple yet accurate digital speedometer circuit using just a single IC, seven segments and a few external passive components. The design can be used for all vehicles for indicating their speeds.

Speedometer Circuit

The main component of this circuit is PIC16F628A. It count signals receive to RA4, then calculate speed and display it on seven segment. A Reed switch used to sense the speed. If the brightness of seven segments is too much, add 220 – 330 Ohms resistors between PORTB and the display. There are two version of hex files are available. In v1 micro-controller use its internal oscillator and v2 used external 4MHz oscillator.

Measure the radius of the wheel and enter it to Eeprom address 0x00. Default value for radius is 30cm (0x1E). You can change update interval by changing the value of Eeprom address 0x01. Default value is 20 (0x14). To increase the sensitivity in this circuit I used two magnets.

Eeprom Settings

Maximum Speed is 999 Kmh
Maximum Radius is 255 cm
Supply voltage is 5v

Circuit Connection

SSD Speedometer

Read More

Simple LED Light Meter Circuit - LB1403

A light meter is a device having a light sensor at one end and a window at the other end which displays the reading that indicates the current light conditions. Light meters are often used in the fields of cinematography, photography and also in test cricket in order to determine the optimum light level for a scene.

Using LB1403 IC and LDR, we can able to build a cheap light meter. LEDs are used to observe the current light conditions and variable resistor is used for adjust the sensitivity. If the LEDs are too bright, change R1 value (220 - 470 ohms). Supply voltage is 6 - 12V.

Light Meter Schematic

Read More

Simple Automatic Brightness Control Circuit

Automatic Brightness Control is the automatic adjustment of the exposure factors such as mA and V. ABC is used to keep the brightness of the display or bulb at a constant level. It involves the adjustment of the V and mA automatically depending on the part of the anatomy being examined. This can be achieved using a LDR, for instance, which monitors the ambient light and change its resistance this resistance changing use to adjust the V, the mA (or both) accordingly.

Automatic Brightness Control Circuit

This simple auto brightness adjusting circuit composed with a LDR. The LDR connected with the Base pin of the PNP transistor. By the LDR feature that its resistance changes with the ambient light, the voltage of Base change. When the ambient light is bright, the resistance of LDR is low, and the voltage of Base is reducing and the ambient light is low, the resistance of LDR is high, and the voltage of Base is rising. Then the output voltage of transistor is changing. The variable resistor is use to adjust the sensitivity of circuit. Supply voltage for this circuit is 12v.

Light Dependent Resistors (LDR)

A Light Dependent Resistor (LDR) is a resistor that changes in value according to the light falling on it. An LDR commonly has a high resistance in the dark, and a low resistance in the light.

ABC Circuit

Read More