One-digit display

The figure shows a one-digit digital display test experimental circuit. It is composed of a self-excited multivibrator composed of NAND gate IC1, etc., which serves as a clock signal generator. The white LED lights up when the level is high. IC2 and other components form a synchronous add counter. The red, green, yellow and blue LEDs display the levels of Q1~Q4 respectively, and also serve as the signal level display of the four-wire input terminal of IC3. The button switch SB2 is the reset switch. IC3 and other components form a seven-segment latch decoder, which converts the input BCD code into the seven-segment output signal required by the digital tube. The button switch SB3 is the light test control switch, SB4 is the blanking control switch, and SB5 is the data latch control switch. The one-digit digital display is composed of a common cathode seven-segment digital tube. R11~R17 are current limiting resistors for the digital tube LED chip. R18 drives the decimal point LED and serves as a power indicator.

When the power switch SB1 is turned on, the decimal point of the digital tube is lit. When the white LED flashes, the red, green, yellow and blue LEDs are lit or extinguished, and the digital tube displays the number. Press the IC2 reset switch SB2, the red, green, yellow and blue LEDs are extinguished, and the digital tube displays O. Press the IC3 light test control switch SB3, the digital tube displays the number 8, and does not affect the LEDs of various colors to continue to flash. When SB3 is released, the number is displayed in real time according to the input BCD number. Press the IC3 blanking control switch SB4, the digital tube is extinguished, and it also does not affect the LEDs of various colors to continue to flash and the real-time display of numbers when the switch is disconnected. Press the latch control switch SB5, the digital tube displays the latched number, and does not affect the LEDs of various colors to continue to flash. When the light test switch SB3 or the blanking switch SB4 is pressed at the same time, the digital tube displays 8 or blanks. After releasing SB3 and SB4, the latched data is not affected. Release the latch switch SB5 to display the current number in real time. The digital display circuit can display the counting results, so that we can intuitively see the "number" of the digital circuit. When you see the self-excited multivibrator automatically generate counting pulse signals, the signal light keeps flashing, and the digital tube numbers keep jumping, you will experience the pleasure of a successful experiment!