这里所讨论的电路是一个4位数字式磁带计数器。此电路的优点是可以升、降计数。 电路的设计用了四个74LS190集成块。在60分钟内给出3600步指示(即电机在60分钟内的转数),并可由预置电位器VR1和VR2进行调节。此电路可修改为既适用于放音,又适用于快进,这可以通过控制555产生的脉冲速率来实现。 The circuit discussed here is a 4-bit digital tape counter. The advantage of this circuit is that it can rise and fall. The design of the circuit uses four 74LS190 manifolds. 3600 steps are given in 60 minutes (ie the number of revolutions of the motor within 60 minutes) and can be adjusted by preset potentiometers VR1 and VR2. This circuit can be modified to apply to both playback and fast forward, which can be achieved by controlling the pulse rate generated by the 555.