Wiimote Project

General Wiimote and Technology => General Hardware Talk => Topic started by: FrankVDL on March 24, 2008, 10:53:39 AM

Title: IR Led Frequency
Post by: FrankVDL on March 24, 2008, 10:53:39 AM
To increase the lifespan of the battery powering the IR-led(s),
you could use a simple chip to make it oscilate.

Does anyone knows the minimum frequency the Wiimote needs, to see the IR-led as 'ON' ?

Title: Re: IR Led Frequency
Post by: microcontrolled on April 16, 2008, 11:27:32 PM
I haven't verified it, but I remember hearing that the IR Sensor operates at 100 Hz, so I would guess that you would need to oscillate your IR LED at at least 200 Hz. Check out some info on Nyquest Frequency.

Hope that helps.
Title: Re: IR Led Frequency
Post by: inio on April 17, 2008, 11:47:41 AM
The sensor actually runs at 200Hz, we're just only seeing every other frame for some reason (the Wii console itself gets updates at 200Hz somehow).  To get good detection you'd probably want to pulse the LEDs at at least 600Hz.

However, this won't lengthen the lifespan.  LED aging is slightly above linear with current, and light emission is typically about linear.  Just using a bigger resistor will give you the same effect.
Title: Re: IR Led Frequency
Post by: Maxx2206 on June 06, 2008, 07:58:52 AM

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...