Show Posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.


Messages - Maxx2206

Pages: 1
1
General Discussion / Re: Infrared LED Battery Life
« on: June 06, 2008, 08:37:53 AM »
one additional note:
maybe the one telling you they should last longer was just confused by comparing battery lifetime of e.g. remote controls and led lights/lamps.
he was misleaded then. typical ir led uses like remote controls emit light in modulated signals and not a continuous stream (typically 36-40khz square/digital signals), resulting in a significantly lower current drain.

2
General Discussion / Re: Infrared LED Battery Life
« on: June 06, 2008, 08:21:05 AM »
hi,

The little coin-sized batteries in a set of glasses must not last very long if they're powering IR LEDs. Someone told me IR LEDs should actually drain a battery LESS than regular LEDs, but my experience shows otherwise.

certainly not true.
standard leds usually want 10-20mA current for a good visibility.
low current leds reduce this requirement to 1-2mA. their visibility is still good, but they (obviously) arent as strong as standards regarding their emission (check the datasheets, they should state the emission intensity in mW, sometimes at different current levels).

for ir leds to work as intended, this emission usually needs to be quite high (the higher the better), therefor most ir leds are built for MUCH higher currents... typical leds are specified for 20-50mA, most of them even work up to 100-150mA limits. some special high performance ir leds for very long range uses even work with 500mA+.
generally, ir leds driven with less current than you would drive standard leds with (<20mA) most likely wont give you good results.

if you want to make the most out of your battery lifetime and still get as good results as possible you should
1. use the wavelength the sensor is most sensitive to (apparently 940nm for the wii camera, 950nm - which is quite a standard - should work, too and give much better results over other ir leds in the 850's range).
2. use leds with the best mW/mA ratio you can find.

3
General Hardware Talk / Re: IR Led Frequency
« on: June 06, 2008, 07:58:52 AM »
hi,

well, since he was asking about battery lifetime and not led aging this is only partly true.
driving the leds via pwm will definitely increase battery lifetime.

not sure if this affects the signal strength of the camera chip, tho. basically, "analogue" photosensive materials will show a difference. digital chips however work different and only simulate certain behaviour of analog sensors (including photosensitive chemicals as found in old cameras).

in theory, the influence should IMO be relatively small since pwm means 100% current but only e.g. 50% duration and the digital conversion is based on fixed timings. if the image sensors convert the peak signal, pwm driven led sources should show no difference. but thats just a guess, i'll hook up some ir leds to a uC later at different frequencies (same current tho) and check the results on a digital camera and a webcam for comparison...

4
Other / Re: I Built An IR Array That Didn't Work
« on: June 02, 2008, 04:12:08 AM »
hi,

wat kind of 9v battery was that?
im just curious since 96 leds would drain those standard 9v block batteries in a vers short amount of time unless you limit the current to a very low level. but that would also mean a very low ir emission level, resulting in poor results.

as for the parallel mode... have you wired them ALL parallel and used a limiting resistor or was it a mixed serial/parallel drive to avoid the resistor? what was the real led current in your circuit?
most ir leds state standard operation at 20mA, but at a relatively low emission rate. 50mA - 100mA is usually where they really shine bright, but that's a real battery killer and you should instead consider using less leds+reflectors+higher current for better results.

5
Other / Re: pulsed (pwm) leds?
« on: June 02, 2008, 02:20:09 AM »
hi,

sorry to disagree, but pwm on leds DOES save you power.
this is simply caused by the fact that the leds will be driven less than 100% (not continuously). a 50% pwm cycle will save you right those 50% batterie power over time. hence why all modern led flashlight applications use pulsed drive and achieve up to 50 hours and more with 5-10 leds driven out of 3 AAA batteries. the only thing to keep aware of is the reduced total light emission, but the exact ratio depends on running some tests.

so, the question wasnt if it saves current (as it does for sure), it was more the pwm frequency that would be needed to ensure safe and stable reading.
since the camera should scan at up to 200hz (gathered from various sources) i would think that 10 times this frequency would be the least to use. so 5-10khz seem a good choice.
anyway, im going to buy a bunch of 940nm leds later and run some simple tests myself. since my camera isnt desoldered i'll have to use the much simpler and much less accurate wiimote-tester app to see if theres a difference in dot size or recognition safety at different pwm settings.

6
Other / pulsed (pwm) leds?
« on: June 01, 2008, 09:03:26 PM »
hi,

has anyone yet successfully tried to use pwm driven leds for head tracking projects to save power?
i was wondering if driving the leds (preferably 940nm since thats apparently the highest sensitivity wavelength) with e.g. a small ATiny uC and pulse the output at some 10khz and 20-50% active state would still be sensed properly by the module or if it would result in noticable loss of quality.
i just began experimenting with the wiimote and im still away from actually deslodering the module (unless someone finds out where to buy them anyway ;) ), so maybe someone who already started using the module independently via i2c could run some tests and see if pulsing the leds would still give stable and strong readings.

in theory the scan should still be good if the pulsewidth is high enough, even with shorter active states, but the battery saving should be remarkable. that would be especially convenient for head tracking projects where people want good recognition without the need to build a massive ir led array (which would most likely be mandatory if you want to use reflectors and not active leds applied to your head, right?).

looking forward to hear your ideas/thoughts...

7
General Discussion / camera module, any maker known?
« on: June 01, 2008, 08:40:50 PM »
hi,

although theres quite some technical info available about pinout and the i2c protocol, i'd like to know if anyone ever found out who makes those modules or if they are freely available on the market - with the same or at least similar specs?

cyas...

8
General Discussion / Re: Confused IR Tracking
« on: June 01, 2008, 05:20:47 PM »
Hi,

this is my first day playing with the Wiimote after i found Johnny's site and his impressive video tutrials.
I dont even own a Wii (and tbh i doubt i'll get one anytime soon) but I was looking for sensor capable of the ones used in the Wiimote for a long time already for various project ideas.
Soon after getting it to work on my notebook and creating my first TrackIR replacement using the IR camera instead of the accelermeters i noticed the same behaviour.
It seems like the camera enumerates the ir dots continuosly, which makes precise tracking usng more than one IR source more complicated (although there's IMO no better way unless you use e.g. modulated light).

The most promising way to avoid this problem probably is to create a toplevel loop that continuously checks for existance of dots (e.g. if using GlovePIE with code like "if wiimote.dot2vis then...", and whenever you count more than one dot you enumerate the result on your own.
depending on how your led arrangment you could e.g. do that horizontally or vertically based on the dot1x/dot1y value which would probably look somehow like

if wiimote.dot2vis then
 if wiimote.dot1x < wiimote.dot2x then
  var.leftled = wiimote.dot1x
  var.rightled = wiimote.dot2x
 else
  var.leftled = wiimote.dot2x
  var.rightled = wiimote.dot1x
 endif
else
 <decide what to do if you lost a dot>
endlif

this is just a thought and not actually taken from a working example but generally it should work.
btw. this one would do a horizontal sort, the decision which dot is left or right would depend on your Wiimote setup (placed towards the user or away from him).

the same scheme should be easily adoptable to any other api.

let me know what you think about it.

Pages: 1