Classic Display Notes

[Harald]

(07-03-2019 10:16 AM)teenix Wrote:  

(07-03-2019 08:39 AM)Harald Wrote:  Wow! How did you do that?
I did not see a chance of getting it to work without the DMA. Thats why I went for the renesas controller.

Cheers,
Harald

It was a bit of a surprise to me also. Except for the power supply everything is bread boarded with flying leads. It was squinty eyes and a nervous finger on the power switch

The PIC can collect and output the Anode data in 375nS plus a small time needed to detect when to do it. I suspect the inductor charge time is eaten into a little bit but the display seems bright enough.

I am yet to hook up the scope to see what it happening on the inductors. Even though the LEDs light up ok, it might be doing it just barely, but I think I have another trick up my sleeve to all but eliminate the latency.

cheers

Tony

Hi Tony,

I am very keen to see your design.

You have to be careful not to charge the inductors without any of the cathode transistor turned on. That will result in an overvoltage that will sooner or later destroy the anode drive. I have solved this by soldering a green LED across one of the cathode transistors. That dissipates the energy and saves the anode driver. Also it indicates if you still have any glitches (I did at startup) that cause problems. The original HP hardware has a startup problem too, but only a very short pulse occures.

Cheers,
Harald

Edit:
To avoid misunderstandings, the green LED was only a temporary measure during development. Once I was satisfied it never turned on anymore I removed it.