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Eric R Snow
- Jan 1, 1970
- 0
Would a white LED, a Luxeon Star for example, be useful as a strobe
light for checking engine timing etc.?
Thanks,
ERS
light for checking engine timing etc.?
Thanks,
ERS
Would a white LED, a Luxeon Star for example, be useful as a strobe
light for checking engine timing etc.?
Would a white LED, a Luxeon Star for example, be useful as a strobe
light for checking engine timing etc.?
Eric said:Would a white LED, a Luxeon Star for example, be useful as a strobe
light for checking engine timing etc.?
Thanks,
ERS
Robert Monsen said:I built a strobe out of white LEDs a couple of months ago, and had fun
'stopping' an AC fan I had in the window. My kids thought it was cool,
particularly when I started using different rates, showing more fan
positions.
It worked quite well, even with cheap LEDs; I built it out of a PIC chip
and a big current mirror, with 10 or so LEDs. The brightness was
adjustable using a pot. I used a fixed 1% duty cycle (adjustable using a
constant in the software), and a variable frequency based on the A/D
converter. Simple software, took about 15 minutes to write.
I'll post the software/schematic if anybody is interested.
If you pulse it properly, I see no reason why not. Look up the pulse spec
on the LED. The pulse width translates into how wide of a smear the timing
mark makes. I've seen backyard mechanics use white "metal-marker" to
emphasize the timing mark on their unit. Not with an LED timing light, but
the principle is the same. The challenging part would be the pulse-forming
network to get the pulse as narrow as possible.
Then again, a one-millisecond pulse is probably not that hard to
accomplish electronically, and it is without question narrow enough to get
your timing within less than a degree.
Would a white LED, a Luxeon Star for example, be useful as a strobe
light for checking engine timing etc.?
Thanks,
ERS
I wonder if the conversion phosphors change the pulse shape; that well
might slow it down. Gotta try that some time.
Don said:I'd throw an eyeball over that...
Good observation I'd forgotten to consider. I use such phosphors (not these,
but 'such') regularly. Their response times are an exponential decay with a tau
in the roughly 1ms-1.5ms range at typical temperatures (it varies from say 5-8ms
at liquid nitrogen temps to tens or hundreds of microseconds at about 400 C.)
Jon
3600 RPM (we're checking the advance here) spins 360 degrees in 16.6
milliseconds. So a millisec flash is 22 degrees. Even at 1000 rpm, 1
msec is 6 degrees.
What do they use for white LEDs... yag powder or something. Phosphors
are interesting; tau's go from under 1 ns to hours.
Robert Monsen said:
Dr. Flash, Harold Edgerton, used to set a sheet of newspaper on fire
with his strobes. Yeah, not too shabby! They used them in airplanes to
take pics of cities.
Watson said:It's a big waste of transistors. Replace each transistor on each LED
with a short. The 10 ohm resistors will drop 1 volt at 100 mA, and the
LED forward V drop will be about 4V at that current, so the total will
be about 5V. The LEDs will easily handle that much current at such a
low duty cycle. And the peak light output will be much higher and
brighter. And that's what you're looking for: a lotta light for a short
time, which is what a strobe puts out.
Dr. Flash, Harold Edgerton, used to set a sheet of newspaper on fire
with his strobes. Yeah, not too shabby! They used them in airplanes to
take pics of cities.
Robert Monsen said:Thanks for the analysis. Your comments are as sagacious as usual.
The transistors are used to control the flash from the PIC. Without the
transistors, you don't have a flash. I guess you could use a big power
transistor to control the 10 LEDs, but this was cheaper for me, since I
had them laying around. They can easily handle the 20mA to 100mA per flash.
The current through the transistors during a flash is controlled by the
pot, which enables the brightness to be changed between very dim to
fairly bright without toasting the LEDs.
I bought a bag of those PNP transistor on ebay recently, so I have lots
of them. They were a 3 cents apiece, but I'm guessing you could get them
cheaper. They are similar in rating to 2N4403s.
[snip]
Eric R Snow said:Would a white LED, a Luxeon Star for example, be useful as a strobe
light for checking engine timing etc.?
Thanks,
ERS
Greetings Robert,I built a strobe out of white LEDs a couple of months ago, and had fun
'stopping' an AC fan I had in the window. My kids thought it was cool,
particularly when I started using different rates, showing more fan
positions.
It worked quite well, even with cheap LEDs; I built it out of a PIC chip
and a big current mirror, with 10 or so LEDs. The brightness was
adjustable using a pot. I used a fixed 1% duty cycle (adjustable using a
constant in the software), and a variable frequency based on the A/D
converter. Simple software, took about 15 minutes to write.
I'll post the software/schematic if anybody is interested.
Watson said:Are you sure that the numbers on those transistors are 2N3566? My old
Motorola manual shows the 2N3566 as being a silicon NPN, similar to the
MPS6514.