Keyscanning question

Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

Threaded View
Ok,

I know this has come up recently...

I am doing a keyscanning app, around 96 keys or so.

1. Can I put the blocking diodes in such a way that I don't incurr a
voltage drop?

I am working with a low-voltage system and schottkys still erode noise
margin.  I haven't come up with a clever way on my own yet.

2.  Keyboard PCB is two layers.  Should I flood fill the bottom layer
with GND to reduce EMI?

I am worried that with additional GND copper, I will increase
capacitance on the long keyboard traces (2 ft).

Thank you.
HW.

Re: Keyscanning question

Quoted text here. Click to load it

if voltage drop is a concern you have a bad input circuit in use.
Rubber keys have a reasonable resistance >0 Ohm and they should work.
Diodes are only required for 3 key combinations otherwhile you can drop them
completely
 
Quoted text here. Click to load it

dont use matrix or change the input threshold to proper value. Eg. use
schmitt trigger buffers for input.
 
Quoted text here. Click to load it

You can make a GND plane but there are more important things for
reliability: For proper ESD behavior decouple XY matrix with resistor
networks of several kOhms against IO buffers. Make a clear gap trace in pcb
and bridge this gap for signals with high impedance resistors only. VCC and
GND crosses that gap with differential coil only what is high impedance for
AC and low impedance for DC. Note: Keyboards and mainly thin membrane
keyboards are one of the practically most vulnerable entrance for static
discharge becouse charged users most time touch the keyboard first
 
Quoted text here. Click to load it


Site Timeline