hi-lo pulse rate discriminator - one bit frequency meter

one bit frequency meter The circuit described here gives a visual indication whether the rate of an incoming pulse train is above or below a predetermined value. Based on a type 74LS123 dual retriggerable monostable multivibrator (MMV) with clear, it should find ready application in microcomputer systems operating with more than one clock, for in- stance a TRS80 with speed-up modification. The reference rate, fr, is determined by the time constant R1C1, which 84454-1 MMV1,MMV2 = IC1 = 74LS123 with the values as shown amounts to 0.45 μs to give fr = 2.2 MHz. When the rate of the input signal, fi, applied to Al of MMV1 lies below fr, output Q1 is able to follow the input 7-88 hi-lo pulse rate discriminator R1 5V 5 msec C2 100n 15 14 ^ ^ 7 6 July/august 1984 01 02 signal. Input B2 of MMV2 goes high at the leading edge of the trigger pulse, so that MMV2 accepts the negative edge trigger on input A2. Output Q.2 then goes low, which causes D2, the "low" rate LED, to light. When fi is...