Electronics > Beginners
RGB circuit help
undescriptive:
Hi everyone!
I'm looking to try and create a circuit that will allow me to run an RGB (high power 3x3W or 4x3W - so at least 3A preferably cope with upto 5A) LED.
This in it's self is easy enough - I have used a latching switch and dip switches (with relevant resistors) on the +ve side of the LED to be able to change colours.
My next complication would be to add some kind of momentary switch to be able to change the colour to a different selectable colour.
This should not be additive i.e. LED could be Red+Blue(pink) and then switch to Red+Green(yellow) not to white.
I would like this to be made of all discrete components - no microcontrollers!
I have a kind of working solution (see attached image), but it's not great, too many diodes! the diodes have been put in place to prevent some weird feedback that I don't understand
I have been going round and round in circles trying to work out what I can do to get this to work.
This will be running from an 18650 battery - 3.7v 3000mAh power source
any help would be great!
Thanks for reading!
Zero999:
Please post a proper electrical schematic, rather than a cartoon. It's not easy to follow because it doesn't provide any information about the switch contacts or the transistors.
Nitrousoxide:
From what I can see from the illegible diagram (please use a proper CAD/CAE program), the circuit will not work.
--- Quote from: undescriptive on July 16, 2018, 02:25:58 pm ---My next complication would be to add some kind of momentary switch to be able to change the colour to a different selectable colour.
This should not be additive i.e. LED could be Red+Blue(pink) and then switch to Red+Green(yellow) not to white.
I would like this to be made of all discrete components - no microcontrollers!
--- End quote ---
If you want to cycle between colours, you will need some form of a state machine. This can be achieved through the use of flip-flops (or binary counters) and discrete logic.
For example, you would need 7 states to cover all possible combinations (R, G, B, R+G, R+B, G+B, R+G+B).
Do you have any experience in logic design?
Clearly, after the logic stage there will be a power stage, this may simply consist of resistors and NPN BJT's.
Ian.M:
Three 74HC4067 16:1 analog switches( one each for R,G and B), with as many groups of three presets as you want different colours, rigged as potential dividers, each group feeding R,G and B control voltages to the Yn'th 'way' of the corresponding analog switch, with their Z (common) terminals feeding voltage controlled PWM generators driving low Vgs threshold MOSFETs for R, G and B.
If you don't want full coulourspace analog RGB, omit the PWM generators and replace the pots with DIP switches + pullup resistors.
In either case, you need logic to select the desired colour by applying a 4 bit binary number to the S3:S0 address pins of the '4067 chips (in parallel). This could be a counter, either clocked by an oscillator if you want it to change automatically, or by a pushbutton. If you want a button that changes to a different set of colours when held, wire it direct to all the S3 pins with a pullup resistor.
However it would be a whole lot easier using a 3.3V 8MHz Arduino Pro Mini, with three PWM outputs controlling the MOSFETs, three pots fro R G and B level, and a few buttons to control storing and playing a colour sequence
undescriptive:
Hi everyone,
Hopefully this should clear things up a little (see attached pic)
unfortunately, I can't install any cad software on this machine.
I'm not trying to hold logic states - just jump between 2 different "paths" - the dip switches will control the colour of each path
Does that make any more sense?
I have seen many circuits for changing between 2 different LEDs, but they don't cover what to do if it's the same LED package
If there is anything else I can clarify, please let me know!
This circuit does work, however, I'm sure there is a much better way of doing this that I'm just not seeing!
I have limited experience in designing circuits (I'm much better at code) so if someone was to totally rebuild this from scratch, I wouldn't be opposed. I'm willing to learn where I'm going wrong!
Thanks again!
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