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Step 8Build the LED Glasses
Okay, this is the easiest part, so of course I buggered it all up. I'll walk through what I did while pointing out the numerous mistakes as we go. Hopefully, you'll then be able to avoid them, or at least feel really dumb if you don't.
I already pointed out that these are single channel glasses, not taking advantage of that high tech switch thingy we installed in our decoder unit. Only one set of LEDs. And only two LEDs per eye, right next to each other. When experimenting with the breadboarded circuit, I checked to see if two LEDs would be sufficient to see through closed eyes. They were. It wasn't until after I had built the glasses that I realized two LEDs were bright enough if they were facing my retinas and my retinas were facing them. Change the angle of either, however slightly, and all you get is a faint suggestion of light. My next pair of glasses is going to have at least three LEDs per line for each eye, spaced about three quarters of an inch apart, in a star pattern (well, triangular, but if there's two lines...)
Anyway, I took a pair of safety glasses and marked on the lenses what I thought was the center of my field of view when my eyes were relaxed. Then I placed the LEDs slightly above that. I did this purposely. The idea was that my eyes would automatically look upwards towards the flashing light. Studies have shown that closing your eyes, consciously relaxing, and rolling the eyes upward causes the brain to produce alpha waves. I figured I'd get a free boost to the efficacy of the glasses this way. There were a couple of things wrong with this reasoning:
The LEDs for each eye are wired in parallel, and the two eyes are wired in series. So in my glasses, the positive (signal) wire runs to the anodes of the LEDs in the right eye, which are connected to each other. The cathodes (marked by the flat side, remember) of those LEDs run to the anodes of the LEDs in the left eye. The cathodes of the LEDs in the right eye are connected to the ground of the audiostrobe jack. I cut one end off of an audio patch cable rather than cut up a pair of headphones, so I've only got one ground wire. If you use headphone cables, you should tie the two ground wires together.
I just used the LED leads to connect to each other, as you can see in the first picture. I used a scrap piece of wire to connect the cathodes of the right eye to the anodes of the left. The ground wire is encased in an extremely ill-fitting piece of heat-shrink tubing. The cable is epoxied to the front of the glasses; the connection stops at the hinge for the stem. You can see the unused channel's signal wire waving forlornly in the wind. If I hadn't epoxied the LEDs, I could go back and install another channel, but with my LED placement problems, I'd rather just build a new pair from scratch.
I used high brightness red LEDs. My next pair will likely have red and blue. Which brings up the problem of R2 that I mentioned back in the parts list. In theory, each LED array needs a different value current limiting resistor. This resistor (R2) ensures that the LEDs don't draw so much current they blow themselves out.
This pair of glasses has a 2x2 array; 2 parallel arrays of 2 LEDs in series. The LEDs probably have a forward voltage of 1.9v and a typical 20mA current requirement. If we changed to, for example, blue LEDs, which have a higher voltage drop, the value of R2 needs to change. Similarly, adding resistors to the array changes the value needed for R2. The easiest way around this would be to remove R2 and replace it with a bus wire. Then wire the correct value resistor inline with the LED array on the glasses. This way, you can swap out glasses without worrying about the resistor value.
On the other hand, it probably isn't a huge deal unless you make glasses with wildly differing resistor needs. I suspect Audiostrobe uses PWM to vary the brightness of the LEDs. PWM can be used to overdrive LEDs far beyond their maximum current, increasing their perceived brightness greatly. It works by rapidly switching the LED on and off. The brightness can be modulated without changing the power applied by altering the amount of time the LED is on and off. Because the LED is off a significant portion of the time, it doesn't overheat. But it flickers on and off so quickly we see it as being continuously on. If that's the case, you likely won't have any problems even if you don't change R2. But when I rebuild my glasses, I'll probably swap out R2 for a bus wire and integrate the resistors into the glasses.
I know some people suggest blacking out the lenses to decrease ambient light. I myself prefer not to walk into walls while moving from the computer to the La-Z-Boy, and instead opt for the more old-fashioned method of turning the room lights out upon getting situated. I would suggest that blacking the lenses might be a good idea if, for example, you're using the glasses to reduce stress on a plane before a flight, but I highly doubt you'd get this thing past those highly trained TSA employees.
I already pointed out that these are single channel glasses, not taking advantage of that high tech switch thingy we installed in our decoder unit. Only one set of LEDs. And only two LEDs per eye, right next to each other. When experimenting with the breadboarded circuit, I checked to see if two LEDs would be sufficient to see through closed eyes. They were. It wasn't until after I had built the glasses that I realized two LEDs were bright enough if they were facing my retinas and my retinas were facing them. Change the angle of either, however slightly, and all you get is a faint suggestion of light. My next pair of glasses is going to have at least three LEDs per line for each eye, spaced about three quarters of an inch apart, in a star pattern (well, triangular, but if there's two lines...)
Anyway, I took a pair of safety glasses and marked on the lenses what I thought was the center of my field of view when my eyes were relaxed. Then I placed the LEDs slightly above that. I did this purposely. The idea was that my eyes would automatically look upwards towards the flashing light. Studies have shown that closing your eyes, consciously relaxing, and rolling the eyes upward causes the brain to produce alpha waves. I figured I'd get a free boost to the efficacy of the glasses this way. There were a couple of things wrong with this reasoning:
- Contrary to what I expected, the eyes don't naturally gravitate towards the flashing light while using the machine. They gravitate towards the at rest position, which I had carefully marked on the glasses before placing my LEDs elsewhere.
- If the LEDs were in the center of my field of view, I'd likely be able to see the pulsing no matter the position of my eyes. As it is now, I can only see it if I consciously look up. Since the entire point of brainwave entrainment is to reduce the activity of the conscious mind, this method is not entirely reliable.
- It only occurred to me after I built the glasses that I don't always want to produce Alpha waves. If using the machine for meditation, for example, I'm likely trying to reach Theta. If it had worked like I planned, the placement of the LEDs would actually be hindering my progress rather than aiding it.
The LEDs for each eye are wired in parallel, and the two eyes are wired in series. So in my glasses, the positive (signal) wire runs to the anodes of the LEDs in the right eye, which are connected to each other. The cathodes (marked by the flat side, remember) of those LEDs run to the anodes of the LEDs in the left eye. The cathodes of the LEDs in the right eye are connected to the ground of the audiostrobe jack. I cut one end off of an audio patch cable rather than cut up a pair of headphones, so I've only got one ground wire. If you use headphone cables, you should tie the two ground wires together.
I just used the LED leads to connect to each other, as you can see in the first picture. I used a scrap piece of wire to connect the cathodes of the right eye to the anodes of the left. The ground wire is encased in an extremely ill-fitting piece of heat-shrink tubing. The cable is epoxied to the front of the glasses; the connection stops at the hinge for the stem. You can see the unused channel's signal wire waving forlornly in the wind. If I hadn't epoxied the LEDs, I could go back and install another channel, but with my LED placement problems, I'd rather just build a new pair from scratch.
I used high brightness red LEDs. My next pair will likely have red and blue. Which brings up the problem of R2 that I mentioned back in the parts list. In theory, each LED array needs a different value current limiting resistor. This resistor (R2) ensures that the LEDs don't draw so much current they blow themselves out.
This pair of glasses has a 2x2 array; 2 parallel arrays of 2 LEDs in series. The LEDs probably have a forward voltage of 1.9v and a typical 20mA current requirement. If we changed to, for example, blue LEDs, which have a higher voltage drop, the value of R2 needs to change. Similarly, adding resistors to the array changes the value needed for R2. The easiest way around this would be to remove R2 and replace it with a bus wire. Then wire the correct value resistor inline with the LED array on the glasses. This way, you can swap out glasses without worrying about the resistor value.
On the other hand, it probably isn't a huge deal unless you make glasses with wildly differing resistor needs. I suspect Audiostrobe uses PWM to vary the brightness of the LEDs. PWM can be used to overdrive LEDs far beyond their maximum current, increasing their perceived brightness greatly. It works by rapidly switching the LED on and off. The brightness can be modulated without changing the power applied by altering the amount of time the LED is on and off. Because the LED is off a significant portion of the time, it doesn't overheat. But it flickers on and off so quickly we see it as being continuously on. If that's the case, you likely won't have any problems even if you don't change R2. But when I rebuild my glasses, I'll probably swap out R2 for a bus wire and integrate the resistors into the glasses.
I know some people suggest blacking out the lenses to decrease ambient light. I myself prefer not to walk into walls while moving from the computer to the La-Z-Boy, and instead opt for the more old-fashioned method of turning the room lights out upon getting situated. I would suggest that blacking the lenses might be a good idea if, for example, you're using the glasses to reduce stress on a plane before a flight, but I highly doubt you'd get this thing past those highly trained TSA employees.
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Sep 29, 2009. 10:07 PMronmaggi
says:
or you could put them on after you sat in your lazyboy...
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