Using 3 wires to control parallel LCD display

[username 198]

Very nice work! Just tried it out today and it works great! Most impressive and thanks for the share!

[chytech 0]

good 

[roadrunner84 466]

I'm sorry if this is a bit late. In your start post you mentioned you want a pulse detector to reduce the pin count from 3 to 2. You were thinking about a 555 timer. You could however use a lowpass circuit to get te desired result.

A low pass circuit would allow you to use a high frequency clock to pass bits to the shift register, while using lower frequency ( in between the bytes that is) to trigger the "E" pin on the display driver.

The great thing about a low pass filter is that you can make them dirty cheap! Basically, you'd use a resistor and a capacitor. You can tie the capacitor between "E" and GND, while the resistor is between "E" and your clock pin. Then a stretched period of "high" would drive "E" high, and a stretched period of "low" would driver "E" low. The time a stable signal need to be there is dependent on the values of R and C, you can find a billion calculators online.

If you don't want to drive high and low for a longer time, but only one of those, you could put a diode from E to the clock pin in parallel to the resistor. Now the capacitor will discharge very fast when clock pulses start, but will only take a longer time to charge again on a prolonged high level.