I'd like to start this new thread to share build notes and other materials for a not-yet-finished at the time of this writing project that started as a collaboration with another forum user Georg in another thread
. Thank you Georg for the project idea!
The laser scanning display project is inspired by this YouTube video by user npaltmp
I could not find more info about the project other than the author's very nice presentation of its features and I wanted to make some changes, so I started my own from scratch.
The initial project requirements I am trying to adhere to were:
- use 8 mirror faces
- use mirror materials other than glass
- use HDD spindle motor or similar BLDC for the rotating mirrors
- use TTL controlled laser diode driver
- have Arduino act as a USB-connected character display device with potential future integration with LCDProc
I've done several things on this project before starting this message, and the current state of the project is in the picture attached to this post.
I have decided to stick to Georg's suggestion of using pieces of split CDs for the first surface mirrors required in this project. Please note that the trick only worked for me on DVD-R blanks, not CD and not anything factory-made. Additionally, only one brand of DVD-R blanks could separate without tearing up the mirror surface (the aluminum layer that gets burned when the laser records the disk). I used Playo
brand single layer 8x blank DVD-R disks (previously recorded) . Nothing else worked. If you find another brand that splits well for this purpose, please post here. Playo
disks split well and also cuts well just by scissors - very convenient. My issue here - it's an older brand, I don't have any more of them left and don't know who still sells them, so any data about alternatives is appreciated.
I have attempted to create the mirror base from sheet metal but that attempt had failed for I could not devise a way to carefully control the angle of each mirror. As a result of that attempt, I've decided to create a 3D part and have it printed by Shapeways. The part that I have created is available for download/order at Shapeways here: laser mirror holder
. This link leads to the holders that has surfaces for holding mirrors at 0.25° angular difference. I am also trying a similar holder with surfaces at 1° difference.
I have already received the 1° holder and tried it with some encouraging result although they aren't perfect. I am observing a possible divergence from the required angle because the layer of super glue that holds the mirror pieces to the base could not have been applied evenly. So, be very careful with glue, especially with an even more precisely tuned 0.25° holder.
As for the HDD, I ended up using a scrap 2.5" (laptop) HDD for the motor - it appears to have the right size and torque.
The HDD motor is driven at this point (uncontrollably) by a spin up circuit from here
. The circuit is very simple and works a treat but not without its downsides: first of all, it's not auto-starting (i.e. you need to give the rotor a not-so-slight push) and second, when it runs, it flies! I am seeing RPMs in excess of 3,000 for sure at 7.5V power and at higher voltages (9V+) well over 5,000RPM. This is not safe for any part of the device and the problem is exaggerated by the mirror holder not being a symmetrical shape (due to 8 mirror surfaces each at its own angle) is not well balanced and will probably break apart at high RPMs.
I have tried the laser diode output at high RPMs and it appears that the RPMs can be lowered without much problem for the functionality. I would like to keep it down to about 1,200RPM if the timing of the laser diode scanning allows.
This is it so far, haven't moved much further than that. This post was intended as a starter for a thread where I (and hopefully other people) will post notes and question about the Laser scanning display project