Rotary Encoders
To control a heliostat more precisely one sometimes would like to have it be a large servo. This means you can simply set the angle of the mirror axle instead of having to go through some less reliable feedback loop. This can be achieve in several ways. We here discuss the potentiometer and rotary encoder methods.Servo's are obviously good candiates to control heliostats, but they are often not very acurate, or powerfull. If they are accurate and powerfull they can be expensive, so you need something cheaper.
It is possible to use the Pic/Picaxe AD inputs to keep track of the position of a potentimeter (rotating resistor). This is pretty straight forward. You connect the two sides of the potmeter to ground and 5+ Volt, and the moving contact to the AD input of your Pic/Picaxe controller. You need to take care of the noise in the AD conversion.
Using this method you can create a feedback signal for your motor control. THis is a method somewhat akin to what happens in a servo. I tested this method and it works, but it is not as reliable so it needs further development. Controlling the motor using this method requires writing a routine that checks the position of the potmeter, then drives the motor accordingly, a lot like moving in response to a light sensor. You can then set the position and hide the routine for the rest of the software.
The same can also be achieved using a magnetic rotary encoder. These have the advantage that they put out a number, the exact position, in a reliable way. You have them in 8, 10 and 12 bit resolution, for instance the AS5040. To make them work you need to
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