2 Digit up/down Counter using PIC16F628A
This project comes via two circuits on 2 boards. The first circuit is designed around a PIC16F628A. It has been presented on an experimental PC board using surface-mount components and was built in less than 1 hour, with about 2 hours to write and finalise the program. See P1, P2
The second circuit uses a PIC12F629 to produce a 2-Digit Up/Down Counter (see P3).
Both use “In Circuit Programming” via PICkit-2.
P5 Describes the up/down counter displaying the “gear” for motorcycles and racing cars.
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).”
The experimenter PC Board shows the five “In Circuit Programming” pins and a diode on the positive rail to drop the 6v supply to 5.4v. The board also has a 100n surface mount capacitor and two surface-mount transistors. The Up/Down buttons have 22k resistors. 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 microcontroller 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 colour.
If the component is a transistor, the voltage developed between the base and emitter will be about 0.7v.
For more detail: 2 Digit up/down Counter using PIC16F628A
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