[simpits-tech] Arduino victory!

[geneb]

On Mon, 6 Aug 2012, dabigboy at cox.net wrote:

>> An easy way to improve the accuracy of the gauge would be to find out what
>> the min/max drive values are and then use the map() function to map
>> temperature values coming from the simulator to the gauge position.  I
>> used the scaling algorithym(sp?) that map() uses when I did my airspeed
>> indicator demo a few years ago.
>>
>> g.
>
> Hmmm I had not heard of map() before....I just looked it up. If I 
> understand this correctly, it would provide a handy way for me to define 
> a function that matches the curve and units of my temp scale, and then 
> apply it to whatever temp reading is coming from the sim, no? I already 
> found the min/max PWM values for the gauge, what I'm doing now is adding 
> a fixed number to my temp value (since the gauge reads temps down to 
> -50, and obviously I need to send values greater than 0 to the PWM pin). 
> I figured, based on the min and max values only, the ratio of temp units 
> to PWM units (my PWM range is still a bit less than the temp 
> range....about 140 steps over a 170*F gauge). But this does not give me 
> perfect results, and it appears to be for two reasons:
>
> 1: The gauge's scale is slightly non-linear....for example, -50 to 0 is 
> finer than 0 to +50, and anything over 100 gets a slightly different 
> scale also.
> 2: Response of the needle doesn't seem to be perfectly 
> linear with PWM duty cycle; I'm guessing the resistance of whatever 
> element was in the original temp probe on the aircraft is non-linear, 
> and the gauge was just designed to match this.
>

What I did was to use a series of translation functions depending on where 
I needed the needle to be.  For example, if you look at the gauge face in 
the video, you can see that the tick marks aren't spaced evenly round the 
face.  I just coded it such that it would use the right translation range 
given the input value.  That guaranteed that no matter what I fed it, the 
needle would be in the right position.

g.


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