LED SignBoard with PIC 16F84A

The pins RA3 to RA0, are used as outputs driving each column LED. The pins RB0 to RB7 are used as outputs driving signal for each column LED. The 74HC154 (Decoder 4 to 16) is the chip that decodes the signal into a binary digit dekaexapsifio. In the left figure all the pins of the door at a reasonable RA 0 (Low), in which case only the output 0 of the 74HC154 decoder is logical 0 and the others at logic 1. Therefore only the transistor TR1 conducts and powered on the column of Led connected with it. For what Led by this column will turn determined by the logic state will find the pins RB7-RB0 door RB. For example, the left shape, because the pins RB0 and RB4 are logical 0 (Low), the Led D1 and D5 will illuminate.
LED SignBoard with PIC 16F84A - schematic

The remaining Led the column is connected to pins of door RB will remain extinguished. Also will remain switched off and the remaining Led columns because the transistors that supply them with power do not lead me. In the figure you can see the Led light up every time, with the combination of the column gate RA, and columns of the door of RB PIC16F84A. Note that the length of each lighting column with Led is 1 / 16. If you use an external circuit with registers hold data for each combination, the time of Led Lighting can grow. But the circuit will increase to one in our example is not used. Note that in each anode Led a resistance limiting current, which is necessary because the Led and protects the feet of the door RB from the disaster. Timing Circuit For the timing of the processor used a ceramic filter (Resonator) or 10MHz crystal and two 22pF ceramic capacitors Feeder circuit The IC2 stabilize the voltage from 12VDC to 5VDC and capacitors to smooth and filter. If all eight LEDs light up simultaneously, the consumption of the circuit reaches about 90 mA. Stabilizer of the order of 100 mA can be used for security, but use a rate of one Ampere (1A).

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