Olin Lathrop wrote:
> Michael Watterson wrote:
>   
>> 1) repeat rate has to be high enough that leds etc don't flicker.  Below
>> 12Hz is very flickery. Above 20Hz isn't bad (Film used to be 24, but
>> they show each frame twice to give 48). I recommend 50Hz or 60Hz
>> depending on local mains, then if pictures are taken and camera is set
>> for local mains frequency, quality is better.
>>     
>
> That will noticably flicker for most people.  LEDs have sharp on and off.
> You need a few 100 Hz to get them to look steady, especially at low duty
> cycles.  Then the flicker will still be visible as the eyes pan accross the
> light.
>   
The faster you pan, the more noticeable the flicker. Even a few 100Hz is 
noticeable if it's moving.  There are moving stick/wheels with LED rows 
that use this to draw flickery text.

Using the series resistor at the PIC and a suitable capacitor, then 
wires to the LED will reduce flicker and RFI.

Same applies to driving moving coil/iron physical meters. at lower 
frequency you may see the needle blur and may hear a buzz. So some sort 
of basic RC filter incorporating the R the meter or LED needs may be a 
good idea.

I use PWM to vary brightness of an LCD back light. Perhaps because it's 
a larger area, the flicker effects being accentuated by movement are 
less. I will check what frequency it is.


-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist