I have a SN74S74N chip that I am experimenting with in building a flip-flop.
I'm just using GND and 5V signals (no arduino).
I've powered the chip, pulled preset (pin1) and clear (pin4) high and attached an LED to Q (pin5).
I've left the clock (pin3) floating for now, and attached a jumper wire to data (pin2) that I use to set it to gnd (low) or vcc (high).
The LED is latching fine (only copying D to Q when it receives a clock pulse). But I'm having some trouble understanding the positive-edge, or rising-edge aspect.
With the clock (pin3) floating, it sits stable at 1.5v (low). Now let's assume Q=1 and I've now set D=0. If I then insert a jumper wire from pin3 to 5V , D is not transferred to Q.
So why isn't placing a jumper wire from pin3 to 5V considered a clock pulse, and a rising edge, causing D to be copied to Q ? (after all, pin 3 was at 1.5V (low), and is now set to 5V by the jumper wire (high)
On the other hand, if I place the jumper wire from pin3 to 0V, D is copied to Q. Why is that ? pin 3 went from 1.5V to 0V, how could this be seen as a rising-edge trigger ?
How should I wire the clock pin if simple want to simulate a rising-edge clock pulse using a jumper wire ?