As shown, with a multivibrator composed of 555, will produce a pulse to 74 ls192, seven segment decoding tube can display the digital simulation, but 74 ls192 input signal changes, but the output of 74 ls192 has been to 0, not counting up,
1, to replace 555 with pulse signal source, can count,
2, the output connect a volt meter in 555, at 0.04-4.98 V,
3, put the 555 output on the oscilloscope, almost with pulse signal on the oscilloscope,
Beginners do course design, the requirement with 555 implementation, is about to hand in the plan, save the children