MegaVUmeters

<img align="right" alt="X profile for easy frame construction" src="http://www.boikon.nl/obj/obj0028866" title="X profile" /><img alt="" height="129" src="http://upload.wikimedia.org/wikipedia/commons/thumb/f/f2/VU_Meter.jpg/220px-VU_Meter.jpg" style="float: left;" width="220" /> The idea is to make 2 VU-meters with needles, but to supersize them to near wall size (2 meters tall, 3 meters wide).

The basic construction is to build a metal frame from [ http://www.boikon.nl/pub/cat0000018.php | X-profile aluminium ] or similar material , into which plates are slid, with an extension to the rear to improve stability and provide a place to install the drive servos and electronics.

The frontplate will be 2mm or more acrylic, while the rear and sides will probably be white coloured hardboard. On the rear board vinyl lettering will be attached to create a scale, on the front one at the bottom, some obscuring vinyl will be used to hide the lighting and the mechanics. At the bottom of the main part two fluorescent lights will light up the VU-meter, possibly through a diffusing plate/foil.

The pointer itself is a carbon fiber tube 160-180cm long, 6mm in diameter with 1mm walls. A counter weight at the bottom of the needle balances it out on the axle. The needle will be driven with 2, dampened, inverse parallel mounted high power, high speed (20kg-cm and 0.15 seconds for 60 degrees) RC-servos, via a rod arrangement. As many bearings as possible will be made using ball bearing or spares will be carried.

An AVR microcontroller will convert audio input supplied either from an XLR or jack connector to control signals for the servos, driving them such that they emulate a galvanometer and circuits used on small sized VU-meters.

Adjustments will be provided to make it "more responsive" and to change the curve of the sensitivity, so as to provide an interesting (instead of absolutely accurate) display.

Optionally a red PEAK light will be provided and possibly the needle itself can be made lit by the use of EL-wire.

Preliminary costs: | *Item* | *each* | *count* | *total* | | Front panels, acrylic, 2mm thick 2000x3000mm | � 110,- | 2 | � 220,- | | Aluminium profile ([ http://www.boikon.nl/pub/cat0000018.php | X-profile aluminium ]) 3000mm | � 19.04 | 12 | � 229,19 | | Aluminium profile ([ http://www.boikon.nl/pub/cat0000018.php | X-profile aluminium ]) 2000mm | � 12.73 | 8 | � 101.86 | | Aluminium profile ([ http://www.boikon.nl/pub/cat0000018.php | X-profile aluminium ]) 300mm | � 1.91 | 12 | � 22.92 | | Aluminium profile ([ http://www.boikon.nl/pub/cat0000018.php | X-profile aluminium ]) 600mm | � 3.82 | 4 | � 15.28 | | Bevestigings materiaal profiel | � 150,- | 1 | � 150,- | | Overige platen | � 100,- | 1 | � 100,- | | Naald | � 25,- | 2 | � 50,- | | Servo and electronics | � 130,- | 1 | � 130,- | | Deliveries | | | � 50,- | | | | *Total:* | � 1089.25 | This is very close to the minimum engineering requirements of a VU-meter of this size, 2mm acrylic especially might not be sturdy enough to keep it's shape, thicker acrylic (double thickness) is around 210 euro extra, making the frame far more sturdy (the 20x20mm profile should work, but is dependent on the acrylic plates to keep in shape, there isn't much weight on it) meaning one size up in framesize is around 250 euro extra.

I have asked for quotes from one other supplier of aluminium frame materials, but so far without any response.

I would be buying the servo, electronics and needle first, so I can prove the concept before spending a lot of money on the frame and plates.

People who know cheaper sources of any of the parts (especially frame material and plates) or know better ways to solve some of the problems should contact me at minister.kamps@minvei.nl or on IRC (revspace, eth0 or any of 2 dozen other channels under the nick Ikarus)

Rough sketch of the frame:

<img alt="" src="https://revspace.nl/pub/RevelationSpace/MegaVUmeters/frame.png" title="Basic drawing of the frame" />

Update <a name="update"></a>

I was experimenting with the use of servos to drive the pointer and now I'm wondering if my physics are correct.

Could someone help me out by calculating the force required (in kg-cm) of a servo to move the pointer 90 degrees in 200ms (including acceleration and deceleration). The needle is 6mm thick, 160cm long, weighing 40 grams, it has an equal counterweight (40 grams) in the form of a 6mm thick, 10cm long rod extending to the other side of the pivot point.

I have some numbers already, but I am not entirely certain of their accuracy, so I am not going to post them here for now, so as not to lead people into the same mistakes.

Stoneshop already pointed out that the counterweight is quite insufficient, because of it's shorter arm, so added to the above, is going to be the effect of either not being balanced (having to deal with gravity) or having the counterweight be uh, 640g (which means the forces on that would be equal ? to that on the main needle)

If you solve it or have other questions, get in touch with me on IRC (irc.freenode.net #revspace) or mail me minister.kamps@minvei.nl