Simplest way to produce a lagging pulse (latch trigger) after receiving another pulse (clock trigger)?

Question

I am teaching myself how to use a 74HC595 shift register, and am fairly new to proper digital circuit design. I ran into a question. I am using a simple circuit involving a few LEDs, a switch for data, and a couple of pushbuttons to pulse the register clock and the latch clock. Basically, I can clock in the data, but it won't update the output LEDs until I pulse the latch clock.

I would like to get rid of the latch pushbutton and have it automatically latch pulse after each clock pulse high trigger. I am wondering what the easiest way is to "echo" a pulse from one clock to the next using simple parts? I.e., when I send a Low-to-high on the clock pin, I want another low-to-high-to-low to immediately follow on the latch signal. The latch signal just needs to stay high long enough for the register to recognize it, not necessarily for the same duration as the original pulse. Half a microsecond should be sufficient for the delay and the duration of the following pulse.

It is not simple enough to tie the clock and latch to the same signal. This results in the display always being one pulse behind (as described in the data sheet).

___/-\_________/----\________ Leader clock
____/-\_________/-\__________ Follower latch
... or perhaps some sort of delay line...
___/-\_________/----\________ Leader clock
____/-\_________/----\_______ Follower latch

Could I clone the clock pin to the latch using some sort of MOSFET with a capacitor for delay?

Answer 1

You did not supply a schematic, and that image thing is incomplete .. but anyway.. the maximum rise rate for the clock input is about 100ns/volt with a 5V supply, and setup time is only about 24ns, so a simple circuit can be used- something like this:

^{simulate this circuit – Schematic created using CircuitLab}

If you don't properly debounce the pushbutton switches you will have issues.

Answer 2

Far and away the simplest way is to feed the original pulse into a coaxial cable, and take the delayed pulse from the far end.

You need to get the cable drive right to get an accurate pulse shape : the simplest way is series termination - ensure the cable is driven from 75 ohms (or 50 ohms as appropriate) - use a series resistor at the input end, and feed the output into a high impedance load (most gates are OK).

Now cut the cable to length : about 2/3 foot per nanosecond delay...

This technique used to be used in TV broadcasting studios with huge coils of coax cable to align colour subcarrier signals to within about 0.5 ns - or 4 inches of cable - so that each path from each camera was correctly aligned at the vision mixer.

Simplest is not necessarily cheapest or best...