light switches
- Thread starter Stu
- Start date
SamT
Moderator
reduction in voltage is usually achieved by resistor but I'm not too sure about leds and that.
If a resistor is used then there is no power saved by having the led's dimmer so I reckon there must be some fancy electronics involved (there is a little circuit board in them zipka/tikka things).
soz :?
If a resistor is used then there is no power saved by having the led's dimmer so I reckon there must be some fancy electronics involved (there is a little circuit board in them zipka/tikka things).
soz :?
D
Dave H
Guest
The usual way to dim such devices is the power it with a square wave and then vary the width of the 'on' part of the wave; i.e. if the 'on' part of the wave is 75% of the period of the wave then you get roughly 75% of the light for 75% of the drain on the battery. Due to the way you eye works it looks as though the LED is constantly on.
I've seen people using the PWM output of a PIC processor to achieve a similar result, but single chip solutions are available.
Some of these 'PWM switchers' generate the required voltages from the battery inputs with clocks in the MHz to keep the size of the inductors down. There have been reports that these cause enough EMI to affect compasses. So I would suggest ordinary filament bulbs for surveying work.
I've seen people using the PWM output of a PIC processor to achieve a similar result, but single chip solutions are available.
Some of these 'PWM switchers' generate the required voltages from the battery inputs with clocks in the MHz to keep the size of the inductors down. There have been reports that these cause enough EMI to affect compasses. So I would suggest ordinary filament bulbs for surveying work.
D
Dave H
Guest
Sorry Stu, I got a bit carried away.
The voltage will be the same (you require a certain voltage drop across an LED to get it to work), but the average power will be reduced.
The method of controlling it is called Pulse Width Modulation (PWM). There are plenty of chips that can do this (some take a variable resistor as the 'brightness' PWM control which could be very useful in a lamp)
BUT you need to know how to use them (hence my first post became quickly quite technical) They are available for about a pound from the usual electronic component suppliers.
The Cave Radio & Electronics Group (CREG) have had various discussions about LED technologies in their journals for many years.
Dave H
stu said:
The voltage will be the same (you require a certain voltage drop across an LED to get it to work), but the average power will be reduced.
The method of controlling it is called Pulse Width Modulation (PWM). There are plenty of chips that can do this (some take a variable resistor as the 'brightness' PWM control which could be very useful in a lamp)
BUT you need to know how to use them (hence my first post became quickly quite technical) They are available for about a pound from the usual electronic component suppliers.
The Cave Radio & Electronics Group (CREG) have had various discussions about LED technologies in their journals for many years.
Dave H
I'm sure the Tikka Plus used PWM (presumably the Zipka is simlar).
One easy way to tell, if the frequency is low enough, is to very rapidly scan your eyes across a scene where someone is wearing one (on less than full power), and standing in front of a relatively dark background at night, or hold one in your hand and move it very quickly across your field of vision, again against a dark background at night.
I'm sure on the Tikka Plus, I've had occasions where I've briefly seen a track of spots of light on my retina when scanning past someone who was wearing one.
One easy way to tell, if the frequency is low enough, is to very rapidly scan your eyes across a scene where someone is wearing one (on less than full power), and standing in front of a relatively dark background at night, or hold one in your hand and move it very quickly across your field of vision, again against a dark background at night.
I'm sure on the Tikka Plus, I've had occasions where I've briefly seen a track of spots of light on my retina when scanning past someone who was wearing one.
SamT
Moderator
Dead right that is.
I notice it on the rear lights on the buses in town. (Red LED's these days)
Its a really strangefenom,phene,phenoman err - effect.
Look dead straight at the light - normal - glance away - and you get a trail of lights.
First brought to my attention in a club in manchester (back in the days)
Behind the bar was a little strip (vertical) of leds. looked at it and thought whatever.
looked away - "absa.."
imediatly looked back - just a strip of leds. looked away again - "vodk..."
look back - nothing. look away - "lutvod" - look again, nothing, look away - "ka...abs"
mad effect it was. And I still havent worked out quite how it worked.
Im sure the drugs helped though.
I notice it on the rear lights on the buses in town. (Red LED's these days)
Its a really strange
Look dead straight at the light - normal - glance away - and you get a trail of lights.
First brought to my attention in a club in manchester (back in the days)
Behind the bar was a little strip (vertical) of leds. looked at it and thought whatever.
looked away - "absa.."
imediatly looked back - just a strip of leds. looked away again - "vodk..."
look back - nothing. look away - "lutvod" - look again, nothing, look away - "ka...abs"
mad effect it was. And I still havent worked out quite how it worked.
Im sure the drugs helped though.
