If you flash a LED at 100 hz it appear to be be constantly lit up, as it's above the frequency response of the human eye or optic nerve or whatever. Your senses are not fast enough to see the flashing.
But if you flash 4 LED displays, ie 4 digits in a 25% duty standard digit multiplex, and each one is flashing at exactly 100 Hz and 25% duty cycle (which is above the human ability to see) then why can you see very clearly that the whole 4 digit display is flashing??
I have my own theory, but I'd really like to hear other people's theories.
Can't believe it because monitors set at >70Hz are very stable without any flash.
So I could not build up any theories in this regard...
If you're lighting each display in a four digit display at 100-Hz (one digit displayed every 2.5-msecs within a 10-msec period), you shouldn't see any flicker.
eye the 25Hz phase beat frequency is really visible, and annoying.
I'll wait for more takers before saying my thoughts on it.
But if you flash 4 LED displays, ie 4 digits in a 25% duty standard digit multiplex, and each one is flashing at exactly 100 Hz and 25% duty cycle
It's nothing to do with mains frequency, the 25Hz beat frequency is real and obvious. The complete phase cycle of multiplexing 4 displays occurs at 25Hz, which can be seen easily.
// assuming 4 LEDs on PORTB 0-4
while(1)
{
PORTB = b'00000001';
Delay_us(7200);
PORTB = b'00000010';
Delay_us(7200);
PORTB = b'00000100';
Delay_us(7200);
PORTB = b'00001000';
Delay_us(7200);
}
Firstly, I don't think that there is anything happening at 25 Hz at all.
If we take a wheel spinning at 6000 rpm (100 Hz) that has a blob of paint or something on it, we might be able to see that it is spinning. That would be like having he 4 LEDs
If we hide most of the wheel behind a screen so that we can only see 1/4 of it, the blob will appear for 1/4 of the time, in a smaller area. That will be like having the one LED.
It doesn't really surprise me that it would be easier to see that the wheel is spinning if all of it is view than when only a small part is in view.
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