Close

Accuracy

A project log for 74xx Discrete Clock

A retro-style digital clock based on 74xx discrete logic chips

StephanStephan 08/05/2020 at 13:160 Comments

I've tried my best to _calibrate_ the NE555 to generate a 1 Hz clock. My oscilloscope was not precise enough for that, so I used a simple microcontroller setup based on the [NEO430](https://github.com/stnolting/neo430) to compare the NE555 clock against a Quartz-based reference clock. The deviation in _ms_ is printed via the processor's UART. After some fine tuning of the potentiometer I finally got a "good" 1 Hz clock from the NE555 and sealed the configuration with some nail polish.


It's obvious that the NE555 is not the most precise clock generator on the block. The actual frequency is impacted by the voltage fluctuations and especially by the temperature of the time-defining components. I tested the clock on a warm summer day and after 24 hours I got a deviation of approx. +1800s or 30 minutes. Not good, not bad, but pretty moderate. So I think I will need to replace the NE555 by a more stable (Quartz) oscillator.

I have tried to build a simple Quartz oscillator using two inverters, a 32kHz clock Quartz (obviously) and some resistors and capacitors. But unfortunately, I was not able to get it oscillating...

Maybe anyone out there has a nice idea how to use some off-the-shelve CMOS chips to to the job.


Discussions