I came up with an idea for my first project. Basically I'll be gutting an analog wall clock and replacing the clock face so the hand points to different types of weather. Snow, sunny, thunderstorms, etc. Then there will be an RGB led indicating temperature from violet (cold) to red (hot). The information is fed from a computer.
It's all pretty easy sounding, but a question remains. I think a small servo motor sounds like the best way to move the clock hand. I think it shouldn't really have to take any power when it's not moving. What I can't figure out is how many degrees of movement normal servos have. I'd obviously like to have all 360 degrees of the clock face utilized by weather types.
Servos typically have about 180 degrees of rotation. To get 360 degrees you can use gears.
An alternative would be to use a stepper motor. I believe, for the stepper motor to work, you would need some method of resetting the position when the Arduino is initialized.
A plain old motor with sensors placed at the stop points may also work.
A standard motor with an encoder wheel would do the trick.
When the clock hand reaches the desired position and the motor power is stopped wouldn't the weight of the clock hand then contiue to move the hand by gravity until it pointed down to 6 o'clock? There is no 'holding torque' on a standard DC motor when there is no voltage applied to it and any continous voltage applied to the motor would cause it to turn continously at some speed.
I think a stepper motor with an additional index sensor or absolute encoder would be the best solution.
Check out tomn igoe's stuff. He had essentially the same idea - he uses a clock mechanism to display various information, such as email traffic. This project is detailed in Make: volume 11.
Obviously the way you are gathering the data is different - you can skip the (hard) part where he gets the info from the network, you can use a temperature sensor connected directly to the arduino.
The "how to move the clock hand" stuff though is very relevant.
Here is one link, there is heaps of his stuff out there + in his book "Making Things Talk"
Thanks very much all for the helpful replies! The clock one is especially interesting. I wonder how fast he can make the clock hands move? It'd seem very interesting to me if it only took a bit to move from one random hour to the other.
After knowing servos are commonly 180, I set out seeing if there were any that were more towards 360. I think I found one, so I'm going to go with that and see how it turns out! http://www.acroname.com/robotics/parts/R298-1T-SERVO.html
If that doesn't work out, I have a box of various stepper motors I'll get to play with.
Something you may want to consider, is normally a clocks hands only spin "clockwise." Using a servo will require the hand to spin backwards when it reaches its full 360 degrees. If thats not a big deal then the servo is probably the easiest solution.
