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Klaas Robers wrote:Why not making an D to A convertor? Just simple resistors in values 1, 2, 4, 8, 16....... ? Or don't you have sufficient output pins for it? The advantage is too that you may do gamma in the analogue domain, two diodes in the emitter chain of the transistor. Then the D to A may be 6 bits , 64 steps....
Klaas Robers wrote:There are certain rules for the precision of the resistors. The resistor for the least significant bit may have a precision of say 30%, as that gives just one step in grey, so if that is somewhat, half a step, more or less, who cares.
The precision goes up by a factor of two each next bit. For 7 bits this goes:
0 : 64k -32%
1 : 32k -16%
2 : 16k -8%
3 : 8k - 4%
4 : 4k - 2%
5 : 2k - 1%
6 : 1k - ½%
This is the reason that DACs are in most cases integrated. It is difficult to make very precise resistors, but in an IC you can easiliy make resistors that have the same value. By circuiting them parallel or in series you may make a precise DAC. Karen Orton has chosen for discrete resistors, as that is easier understandable.
Klaas Robers wrote:It should be possible to output a digital number to a 8 pin output port in one instruction, isn't it? That is faster than what you can think of. The Arduino should have parallel digital output ports I suppose. You can connect the resistor network directly to it. In the PIC colour decoder it is also done in that way. And indeed you need no more than 6 bits / pins for 64 steps of grey.
Andrew Davie wrote:You can see it's as precise as my multimeter will let me measure.
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