Small change

A project log for DYPLED

a thin LED display in SIP module format, much better than TIL311s to visualise your computer buses

yann-guidon-ygdesYann Guidon / YGDES 04/11/2016 at 06:270 Comments

I haven't progressed much lately but I have encountered several use cases for the DYPLED module :-)

I recently found this circuit on the web :

This is an amazing solution to reduce the proliferation of buttons on the board, and save some space, and make it easier to route...

(of course, forget the useless 2N3904)

Edit: I also decided to drop the "blank" input. I wonder if this feature would be ever used, and it might be a bit confusing.

Furthermore I use 3 LVC1G08, it might be better to use HC08 instead (less crazy routing to the 3×2 power supply pins despite a larger package)

Or I could just use only NC7SZ157 (MUX2) to emulate AND gates. Too bad there is no quad MUX2 in DIP18. I have 74LVC157APWR but the select lines are shared so it's unsuitable for arbitrary logic :-/

Edit: the above Flip Flop works.

I changed the feedback resistor to 10K and the the RC to 100K/100nF and it works nicely. However it is pretty sensitive to finger touches so the pads of the switches should be protected. But otherwise, it's a nice thing.

Only actual drawback: it's not easy to set/reset a latch as with the last method. So I only output one wire, that will be connected to 0V or +3V to force the state. This saves more wires (hence PCB surface and routing) and a couple of pins (one less pin after I removed the blanking input).