How do I monitor an angle?

Yes DAB, define your resolution and develop from there (the three D's - define, define, define). Back to the point of ambient light. Let's assume a high resolution. Using a grey scale ring (presumebly going from black to white along its circumference) and a calibrated reflective led/opto-transistor unit with an optimal focal distance of 5 mm, we will need an interface that will produce an analog voltage that represents the amount of light reflected from the ring (not necessarily linear, it can be calibrated using a lookup table) that will be run into an A/D converter (say 16 bit). Now lets assume our opto unit is sufficiently focused to detect changes in light down to 64,000 parts over the rings circumference (how many pixels does the focal area cover and how many pixels are on the ring). The problem is: changes in ambient light will add an unknown constant error to our voltage, and our reading, and may saturate our opto-transistor under extreme lighting conditions.  If we use a simple resistor / common emmiter setup, we can increase our gain and sensitivity by increasing our resistance, but the transistor will saturate under lower ambient. Or, we can minimise this effect by using a lower resistance, but we sacrifice gain / sensitivity. Saturation has been my biggest problem. In fact, manufacturers go to a great deal of trouble to account for / remove these effects in their interface circuits.

Of course, there are several ways around this:

1: Use a pot. Simple, but they are prone to wear and tear and dirt. Also, start messing with gears and it can get messy.

2: Enclose the unit in a light proof enclosure. Good option, but this adds to the mechanical complexity.

3: Buy a matched detector / interface from farnells. The simplest, but where's the fun factor.

4: Develope your own interface. I have done this and it is a fantastic learning experience if you see it through (it took me years, and the deeper I looked into it, the more satasfying and rewarding it became. I got a real buzz every time I found an improvement or a more elegent solution).

By the way, feedback is always good and my ratings go up (LOL), keep it coming! (cool robot Raimondus)

Yes DAB, define your resolution and develop from there (the three D's - define, define, define). Back to the point of ambient light. Let's assume a high resolution. Using a grey scale ring (presumebly going from black to white along its circumference) and a calibrated reflective led/opto-transistor unit with an optimal focal distance of 5 mm, we will need an interface that will produce an analog voltage that represents the amount of light reflected from the ring (not necessarily linear, it can be calibrated using a lookup table) that will be run into an A/D converter (say 16 bit). Now lets assume our opto unit is sufficiently focused to detect changes in light down to 64,000 parts over the rings circumference (how many pixels does the focal area cover and how many pixels are on the ring). The problem is: changes in ambient light will add an unknown constant error to our voltage, and our reading, and may saturate our opto-transistor under extreme lighting conditions.  If we use a simple resistor / common emmiter setup, we can increase our gain and sensitivity by increasing our resistance, but the transistor will saturate under lower ambient. Or, we can minimise this effect by using a lower resistance, but we sacrifice gain / sensitivity. Saturation has been my biggest problem. In fact, manufacturers go to a great deal of trouble to account for / remove these effects in their interface circuits.

Of course, there are several ways around this:

1: Use a pot. Simple, but they are prone to wear and tear and dirt. Also, start messing with gears and it can get messy.

2: Enclose the unit in a light proof enclosure. Good option, but this adds to the mechanical complexity.

3: Buy a matched detector / interface from farnells. The simplest, but where's the fun factor.

4: Develope your own interface. I have done this and it is a fantastic learning experience if you see it through (it took me years, and the deeper I looked into it, the more satasfying and rewarding it became. I got a real buzz every time I found an improvement or a more elegent solution).

By the way, feedback is always good and my ratings go up (LOL), keep it coming! (cool robot Raimondus)