​First soldering and first limitation.

A project log for BIG_CLOCK

A basic clock using large 7 segments LCD panels

MuthMuth 02/15/2016 at 17:140 Comments

I finally manage to solder the TQFP 80 package of the PIC on the breakout board. Everything seems alright, I can program the chip with the Pickit.

It took me some time to figure out why the RTC was not working. I took a scope and checked the 32.768KHz second external oscillator, and could see a sine wave appearing. And that was the point. The signal appears when I put the scope probe on the quartz pin. The error was a wrong capacitor value. Somehow I put a 100nF cap instead of a 12pF for one of the quartz surrounding grounded capacitors. I don't know how the probe change the circuits impedance and makes it start oscillating, but with the correct capacitor I could now see the RTC running.

A nice thing with the PIC 18F87K90 (let's call it the PIC...) is it can drive 48 LCD segments in static. Which is exactly all the segment I have on the 6 panels. 7 segments for the character and one dot. But... and it seems there is often a but with Microchip... But on the 48 pins able to drive LCD segments, one is multiplexed with the RTC oscillator... (pin 35 mixed SOSCI and SEG32)

pin 35 mixed SOSCI and SEG32

Well, I decided to get rid of one dot ;)

Right now I connected 2 digits and they display the seconds of the RTC. It's working great however I should wait all segments are connected. I'm sure I will have to fine tune the Pic parameters to have nice contrast. After that, perhaps there is nice digit transition to make ? In addition, I have to think of time adjustment buttons.