![]() ![]() See also LED step-up converter with ATtiny85 This ON and OFF periods are small for the eye to pick so we see both displays ON continuously, which is not the case in real. What we are doing is, we are going to trigger one transistor for 10ms and another display for an another 10ms, so the display one will be ON for 10ms and then it turns OFF, during this time other display will be ON. Here we have two transistors each driving current from each display. The important thing here is although both segments share same data port to ATMEGA, the Common Cathodes of both displays are connected to two different transistor collectors. Now as of multiplexing, as explained in introduction we are going to turn ON and OFF displays instead of LED. ![]() PIN3 or PIN8 or CC to transistor collector PIN5 or h or DP to PIN (A, 7) /// Not needed as we are not using decimal point The connections which are done for 7 segment display are as follows: Software: Atmel studio 6.1, progisp or flash magic. Hardware: ATMEGA32, Power supply (5v), AVR-ISP PROGRAMMER, HDSP5503, Seven segment displays (two pieces) (any common cathode will do ), 47uF capacitor (connected across power supply), button(three pieces), 10KΩ resistor (two pieces), 1KΩ resistor, 220Ω resistor (two pieces), 100nF capacitor (three pieces), 2N2222 transistors (two pieces). See also Charlieplexing 7 segment displays using Atmel Tiny26 microcontroller Components Required At this rate the eye pictures the LED with less brightness and that is all. At this rate a human eye cannot see turning OFF cycles at all. But if frequency is increased to 50HZ, that is 50 ON times and 50 OFF times for the LED in a second. Now at this rate a human eye can see both ON cycle and OFF cycle. it ON two times and OFF two times a second. Consider an LED is turning ON and OFF continuously at a rate of 2HZ per second, i.e. It’s simple a technique used to connect more units in parallel to lessen the pins required, by taking advantage of visual effect. ![]() These Common Cathode and Common Anode displays come in very handy while multiplexing several cells together. In Common Anode, the positive of every LED is connected together and brought out as VCC. The circuit connection of LEDs in common cathode and common anode is shown in above figure. Here one can observe that, in Common Cathode, the negative terminals of every LED is connected together and brought out as GND. ![]()
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