Perm Red S

Hansa Yellow AXN

Lamp Black B

Magenta M

Medium Yellow T

Raw Umber L

Red Oxide F

Thalo Blue E

Thalo Green D

White KX

Yellow Oxide C

The specs are the following;

• 109lumen at 350mA
• 243 lumen at max current 1A (assuming one can keep it cool)
• Viewing Angle 80 deg
• Color: Cool white, 6500K
• Size 3mmx3mmx2.23mm high

A full data sheet is available at http://media.digikey.com/pdf/Data%20Sheets/Osram%20PDFs/LUW_CP7P.pdf

The big problem with the above is temperature. Low cost FR4 PCB’s will not provide enough heat sinking.

The Cree MX3AWT-A1-R250-000C51 is another inexpensive LED, running about $1.87 at 250 piece quantities.

The specs are as follows.

• 67 lumen at 350mA
• 100 lumen at 400mA (assuming one can keep it cool)
• Viewing Angle 120 deg
• Color: Cool white 6500K
• Size: 4.65mmx4.65mm

A full data sheet is at http://www.cree.com/products/pdf/XLampMX-3.pdf

Whats nifty about this part, is that one can use a double sided FR4 pcb and through the use of vias under the paddle achieve adequate thermal performance.

1. EF lenses from Canon film cameras will work on Canon digital cameras that use EF-S lenses, the reverse however is not the case. The reason is that EF-S lenses project further into the camera body, and as such they will not fit, and may even damage the mirror mechanism on film cameras.
2. Digital camera sensors are for the most part smaller than 35mm film. The exception being cameras with full frame sensors, such as the Canon 1Ds etc. As a result of this, the lens effective focal length changes, typically by a factor of 1.6. As such a 35-80mm zoom lens becomes a 56-128mm.
3. There may be other factors as time passes, it is always best to check with a competent camera guy before buying something only to be disappointed, or worse, damage your unit.

IR Sensor Discussion

The IR sensors are an array of thin film Bismuth-Antimony thermocouples surrounded by Xenon gas. Active junctions in the center of the detector receive radiant energy through a thin film filter which eliminates wavelengths outside of a 8-14 micron area. Non-active junctions are shielded by the TO-5 can and have reasonably thick bond wires leading to the sensor leads in order to provide some level of heat sinking. The Xenon gas is a bit of a thermal compromise. It was chosen to provide slow albeit decent enough response times for music purposes, but more so to provide greater stability, and less of a headache for dT/dt (temperature/time) events.

High Gain Amplifier

I normally like chopper amps, but since this is a music app, and I dont know if I have any in the junk box I’ll likely go with something more conventional like an OP77. The IR sensor signal is very small, on the order of a few microvolts, so low drift op amps are a must…but obviously noise is a concern as well. The Vos drift spec of 0.3uV/C is a real concern… but if the input amp is kept separate and close to the isothermal block assembly, most of this concern will be alleviated.

The offset/gain block

At this point, the signal is high enough, I can do some serious op amp modifications to it without getting into too much trouble. The biggest issue here is not to run into a wall during processing. The 555 pulse position modulator needs an input range of roughly 0.1-0.9VDC for full scale performance.

The 555 Pulse Position Modulator

The nice thing about the PPM is that it is very non-linear, as will be the output of the long wave IR sensor, add in the issue of even tempered musical scales, and life will be interesting. Eyeball wise, this should work out ok… being Spice is worthless in this topology, I wont know for sure until its up and running and I can make some measurements.

555 PWM and the Voltage Controlled Amplifier

Granted, such is a bit kludgy. However, the intent is to use parts I have sitting around… and the PGA’s I have dont exactly lend themselves to the output provided via a duplication of the above gain/offset design as an input stage. Then again, if this was a production design, I’d just bring the high gain amp output into a ADC and let a processor or even an FPGA work out the non-linearities, as well as creating the output waveform on the fly.

A simplified view of the long wave IR detector is shown in figure 1. The background radiation is ever present, and the detector is mounted in an isothermal block. As a result, the TO-5 can of the detector also serves to emit background radiation at the same color temperature as the ambient environment.

As such, when a human hand enters the viewing area of the IR detector assembly, the radiated energy from the hand results in an increased output voltage. Figure 2 shown below, shows what happens as the human hand is moved back and forth. Namely the output varies as the hand transcends more of less of the detectors viewing area.

Optical Theremins

Many folks have built optical theremins. They are easy to build with low cost components. In a nutshell, a 555 timer could have its frequency controlled via a light sensitive resistor. The output of the 555 would then be amplified with a simple op amp circuit with another light sensitive resistor as part of the feedback loop. One big problem with optical theremins is their sensitivity to back ground light. Ie if the lighting changes, one also has to change their hand positions. This sensitivity to ambient lighting makes consistent performance challenging, and also can make it a difficult instrument to master.

Long Wave Infrared Radiation

My proposed solution uses long wave infrared sensing of human body parts. Specifically human skin radiation sensing in the 8-12 micron range. As skin radiation in this range is fairly consistent once a human has become thermally acclimated to their surroundings, such should provide a more consistent operation. In addition, my solution has automatic compensation for background radiation, albeit the actual process of compensation will be slow, and there are some higher order effects which can come back to haunt the musician. Apart from those, it is hoped that my design will provide a shorter path to mastery of the instrument in comparison with previous designs.

The 555 timer is key

Years ago, I designed a control system using the LM555… cheapness was one of the most critical design criteria, and low cost processors were still many years off into the future. In the process of developing this control system, I learned a number of unique things about the LM555 operating as a pulse position modulator… such is what I hope to leverage in my theremin design.

Timing is going to be tricky… I just came across the deadline for the 555 contest this morning. Entries need to be in by March 1. As such, this weekend should be busy, as I’ll not only have to design the unit, but also build it, test it, and even try to learn to play it. (and somehow or another figure out how to make a video and put it up on YouTube)

Another approach consists of using a welding to build up material in the hole, such that a bolt/washer assembly can be welded to the previously buried broken stud. On the outset, such seems insane… but steel doesnt stick to aluminum, and the flux almost always builds up an insulating coating on the internal threads. I came across the following graphs which show how such is done…

Granted, when a stud is buried, the chances of finding it in a top down vertical orientation is rare. As such, Lawson also provides the following alternative procedure.

A new large turbogenerator in a UK power station was designed to have its 20kA three-phase output busbars split either side of one of its support pillars, because of a lack of space. The support pillars were steel, part of a steel framework, and created a single-shorted turn around one of the busbars. In operation, the pillar (made of 2 inch thick steel members) got hot enough to blister its paint, and increased in height by 5mm, putting a bearing out of alignment and causing a terrific noise which caused the station workers to run for their lives. (Editor’s note: a large turbogenerator up to speed and adrift from its bearings is a fearsome
object!) The cure was another shorted turn, this time around the pillar and made of ½ thick aluminium.
(Conversation at Mersey and District Club Européen, 28th January 1999.

Via http://www.nutwooduk.co.uk/pdf/banana%20skins.pdf

The first outfit that comes to mind is McMaster-Carr… and they do have a huge variety of materials, great service, and with next day delivery to boot. However, they are spendy, and often lean towards more generic than exotic supplies.

Another place is Chimney Sweep Etc. They have a number of refractory and furnace cements. While getting such from a big box hardware store is likely the best option, the limited selection available often makes online a better way to go.

Marinite Insulating board is another nifty material… but its comes in 4×8 sheets, so shipping can be problematic. The tough part is this material leans toward the OEM level… but there are distributors, and in addition, its likely fragile enough that broken pieces are common enough that one could swing a deal at times.

On the other hand, kit oven suppliers may be an option. Forno Bravo has insulating sheets rated up to 2300F in a shippable size. In addition, they have ceramic blanket… but obviously one gives up the advantages of OEM pricing for availability and the ability to purchase small quantities.

Rather than using the image show in this blog post, it would be best to do direct to the homeshop machinist website, and print it from there… I don’t know if this blog software twiddles with the color calibration or not.