Background: I am building a busybox for my 2-year old nephew as a way for me and my partner to get back into electronics and also to keep his busy fingers busy.
I have planned and partly built most of the box and now I just need help with the last part, an RGB LED dimmer circuit. We plan to have 3 slide pots (say 100k each), one for each of the Red, Green and Blue LED's. The idea is that each pot will vary the brightness of one LED from 0 to 100% and he can discover colour mixing and have some fun as well.
I have already purchased the RGB LED's in the form of 3 separate LEDs on a little breakout board from SparkFun http://www.sparkfun.com/products/10111 and it also includes driver transistors (2N3904's).
I am considering the 555 based PWM circuit by Bill_Marsden but I just need to check a couple of aspects and also ask about linear vs log pots. My feeling is that linear pots are required to make the duty cycle vary linearly from 5-95% as Bill states that LEDs are not linear to current, but this PWM circuit will make them appear so, which is one of the reasons PWM is so popular controlling LEDs, but I'd appreciate confirmation in my scenario.
The PWM circuit only gives 5-95% duty cycle, whilst I can live with the 95% limit I would like to be able to turn the LED's off (perceptibly, not absolutely, so if you could see a dim light in darkness that would be acceptable). Another concern is that I'll need three schmitt triggers/555's and so I was wondering if a different chip could be substituted that could service all three LED's in one package, rather than having to use a 556 and a 555. Additionally, the box is going to run off 6xAA batteries (using a SG3525AN to supply the 5v) so I would like to minimise the current consumption and from what I've read the 555's are fairly power hungry compared to more modern devices.
I'm wondering if perhaps I've missed another type of circuit that would be more suitable? I believe that all I need some sort of variable current driver to vary the brightness, so I was wondering if a simpler transistor-based circuit would work? Or perhaps there is a fancy IC thats designed for exactly this sort of circuit? BTW I am aware I could use a micro controller for this, and I do want to start using micro controllers fairly soon but not for this project.
Cost isn't a particular issue for this one-off project but complexity is, as I am planning to construct the circuit 'dead-bug' style, so low component count is important.
Any advice gratefully received and thanks to the forum members who have posted all these fantastic circuits and advice over the years, apologies if my searches have missed somewhere that this or an equivalent question has already been answered.
I have planned and partly built most of the box and now I just need help with the last part, an RGB LED dimmer circuit. We plan to have 3 slide pots (say 100k each), one for each of the Red, Green and Blue LED's. The idea is that each pot will vary the brightness of one LED from 0 to 100% and he can discover colour mixing and have some fun as well.
I have already purchased the RGB LED's in the form of 3 separate LEDs on a little breakout board from SparkFun http://www.sparkfun.com/products/10111 and it also includes driver transistors (2N3904's).
I am considering the 555 based PWM circuit by Bill_Marsden but I just need to check a couple of aspects and also ask about linear vs log pots. My feeling is that linear pots are required to make the duty cycle vary linearly from 5-95% as Bill states that LEDs are not linear to current, but this PWM circuit will make them appear so, which is one of the reasons PWM is so popular controlling LEDs, but I'd appreciate confirmation in my scenario.
The PWM circuit only gives 5-95% duty cycle, whilst I can live with the 95% limit I would like to be able to turn the LED's off (perceptibly, not absolutely, so if you could see a dim light in darkness that would be acceptable). Another concern is that I'll need three schmitt triggers/555's and so I was wondering if a different chip could be substituted that could service all three LED's in one package, rather than having to use a 556 and a 555. Additionally, the box is going to run off 6xAA batteries (using a SG3525AN to supply the 5v) so I would like to minimise the current consumption and from what I've read the 555's are fairly power hungry compared to more modern devices.
I'm wondering if perhaps I've missed another type of circuit that would be more suitable? I believe that all I need some sort of variable current driver to vary the brightness, so I was wondering if a simpler transistor-based circuit would work? Or perhaps there is a fancy IC thats designed for exactly this sort of circuit? BTW I am aware I could use a micro controller for this, and I do want to start using micro controllers fairly soon but not for this project.
Cost isn't a particular issue for this one-off project but complexity is, as I am planning to construct the circuit 'dead-bug' style, so low component count is important.
Any advice gratefully received and thanks to the forum members who have posted all these fantastic circuits and advice over the years, apologies if my searches have missed somewhere that this or an equivalent question has already been answered.