Page 1 of 2 12 LastLast
Results 1 to 10 of 17

Thread: Analog scan rotator

  1. #1
    Join Date
    Mar 2008
    Location
    Sydney, Australia
    Posts
    315

    Default Analog scan rotator

    Hi PhotonLexicon,

    I want to build an analog scan rotator (for any angle, not just flip X/Y).

    Mathematically:
    Xrotated = X * COS(angle) - Y * SIN(angle)
    Yrotated = X * SIN(angle) + Y * COS(angle)

    Can I use an op-amp to compute the COS and SIN functions?

    Kind regards,

    weartronics


  2. #2
    Join Date
    Jan 2006
    Location
    Akron, Ohio USA
    Posts
    1,754

    Default

    This is a classic question for Dean C. Hammonds!

    James.

    PS I'm guessing there might be a way, but not through ordinary linear analog circuits. Sine and Cosine are not simple functions to calculate under any circumstances. Historically speaking, they were found in large books of lookup tables with varying precision; actually measured with drafting tools and real, drawn circles! There are infinite series notations for these things, but much like the relationship between a circle's radius and its diameter, it cannot be fully quantified to any rational value. Good Luck!

    James.
    Last edited by James Lehman; 08-10-2008 at 10:36.

  3. #3
    Join Date
    Mar 2008
    Location
    Canton, GA USA
    Posts
    384

    Default

    I've built rotators before using an analog 4-quadrant multilplier chip.

    http://en.wikipedia.org/wiki/Analog_multiplier

    also: Google "Analog Devices" and "multiplier".

    Tim

  4. #4
    Join Date
    Jan 2006
    Location
    Akron, Ohio USA
    Posts
    1,754

    Default

    Can you give us some more detales, please?

    James.

  5. #5
    Join Date
    Apr 2007
    Location
    Costa Rica
    Posts
    523

    Default

    Here is a rotator I made. Signal path is analog, but the sin and cos tables are digital on eprom so the rotation can be stopped without drifting. Comes with documentation.
    http://cgi.ebay.com/ws/eBayISAPI.dll...m=150281723379

  6. #6
    Join Date
    Jan 2006
    Location
    Akron, Ohio USA
    Posts
    1,754

    Default

    WOW! You made that? That's really neat! Nice job.

    James.

  7. #7
    Join Date
    Aug 2008
    Location
    St. Louis, MO
    Posts
    45

    Default 4qmm

    You need 4 - 4 quadrant multiplier chips - we used to use the AD532 from analog devices. You can certainly use opamps to generate the sin/cos signals - it's called a quadrature osc. As an alternative a joystick moving in a circle does the same thing and allows you to "perform"...

  8. #8
    Join Date
    Mar 2008
    Location
    Sydney, Australia
    Posts
    315

    Default

    Hello all and thank you for your suggestions,

    I am still not sure how it is possible to compute sin and cos using analog multipliers without LUT. I need to compute sin and cos very fast with better than 8-bit resolution, based on the rotation of my spinning projector. This is why I prefer to use the analog circuit, because the delay of ordinary ADC-LUT-DAC is too long.

    I was looking at sine encoders, which output sine wave signal proportional to rotation, but they are many cycles per revolution and I need one cycle per revolution. I thought of an even simpler solution, because the transmission of crossed polarisers is the sin of the angle. I can use a spinning disc of polarising film, geared down 2:1 from the projector using timing pulleys. Then with photodiodes and stationary polarisers on opposite sides of the disc, the output of the photodiodes is the sin and cos of the rotation. This is cheap and simple to make with no digital delay.

    Best regards,

    weartronics

  9. #9
    Join Date
    Aug 2008
    Location
    St. Louis, MO
    Posts
    45

    Default

    You use the 4 quadrant analog multipliers to do the multiplication in the rotation formula. The sin/cos signale are classically (i.e. in my laserium days) provided to the circuit from a joystick moving in a circle. It could also be generated by a quadrature osc. or a look up table - I used to use a military surplus sin/cos potentiometer at one point - of course I haven't seen any of those for 25 years...

  10. #10
    mixedgas's Avatar
    mixedgas is online now Creaky Old Award Winning Bastard Technologist
    Infinitus Excellentia Ion Laser Dominatus
    Join Date
    May 2007
    Location
    A lab with some dripping water on the floor.
    Posts
    9,543

    Default

    Quote Originally Posted by imobscure View Post
    You use the 4 quadrant analog multipliers to do the multiplication in the rotation formula. The sin/cos signale are classically (i.e. in my laserium days) provided to the circuit from a joystick moving in a circle. It could also be generated by a quadrature osc. or a look up table - I used to use a military surplus sin/cos potentiometer at one point - of course I haven't seen any of those for 25 years...
    PM me, I have a schematic for a 12 bit digital rotator. It uses two multipling dacs that are ~$7-$12 in quanity one from AD. I can scan it in and send it as a pdf. I only have Inet access once a week so it may take me time to get back to you (unemployed, no T3 to my desktop net at the office anymore :-( )

    Steve Roberts

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •