LEDs don’t dim well using a an adjustable resistor, instead a pulse-width modulator is usually used to blink them rapidly giving the appearance of less light. Giovanni brings the analog charm back to LED dimming by controlling brightness via an adjustment knob (machine translation). This dimmer reads the value of an adjustable trimmer resistor with an analog to digital converter, and adjusts a the PWM output accordingly.
how about controlling the LEDs with a constant current source – we could vary the output current by turning a resistor – what ya guys think?>
I don’t think that would work…..you would have a _fixed_ brightness level with a CC source. The varying brightness is due to a varying current. But then, in essence, doesn’t the PWM control do this? Varying duty cycle to vary the amount of current (since forward voltage of the LED is fixed)?
i just thought a single transistor CC is simplier [lesser components] compared to the PWM version..just a though havent tried it though
I hear there’s an obscure device called a “555 timer” which can create a PWM waveform using a VR.
Meh, if it ain’t broke – attach Arduinos to it until it is.
You all are right, but don’t you mind that the author wanted to make something to test the ADC and PWM of the chip ? :)
A quad op-amp can generate a triangle wave, then be used as a comparator to create a PWM wave with a duty cycle that is proportional to a DC voltage from a trim pot, all without analog to digital to analog conversions. There was a video and circuit in this blog a while back…
Alternatively, the MAX1561/MAX1599 has a brightness input that accepts either PWM or a DC voltage (from a simple trim pot) to control a switched current source. Very versatile chip, but difficult package.
@Philip, I think your idea will work if the single-transistor CC source is controlled by a trim pot. Just because it’s called a “constant” current source doesn’t mean that the current cannot be changed manually.