Mike Harrison wrote:

> On Tue, 28 Nov 2006 09:59:37 -0200, you wrote:
> 
>>Alden Hart wrote:
>>
>>> It's also worth noting that they tend to use 16 bit controls on the PWM
>>> for dimming. It seems that fewer bits than this (i.e. less temporal
>>> resolution in the pulses) gives you visible steps (quantization
>>> errors) at low light levels.
>> 
>> If you had a log scaled PWM generator, fewer bits would be fine -- most
>> are not, but it's not impossible, depending on the technology used.
> 
> You generally need a minimum of 12 bits, mostly to cope with
> nonlinearity at low levels - you can take a 256 level value and put it
> through a linearising table to give a 12 bit PWM value to get a nice
> smooth fade.

That's why I said "a log scaled PWM generator". I meant a hardware circuit
that translates eg. 256 linear steps of voltage or time into 256 log scaled
steps of time. For example by using a capacitor (dis)charging function.

Gerhard

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