I'm hooking up an Arduino to an automotive power supply which fluctuates between 12 and 14.4 volts. I'm also hooking up RGB LED light strips in this circuit as well, now I'm not afraid of the 14V frying the LEDs, but I do not want the brightness of the LEDs to fluctuate with the voltage. Is there anything I can do to prevent this besides an inefficient 12 V linear regulator?
RGB LEDs in automotive environment with fluctuating voltage
arduinoautomotivevoltage-regulator
Related Solutions
Do you have the DC supplies and Arduino grounds connected together? If not then any PWM from the Arduino will not work.
Most small plug type DC supplies are floating, so their grounds will not be connected to USB ground (of course the USB ground may be floating if e.g. on laptop battery)
As Russell mentioned a diagram of your connections would be useful.
Thanks for the diagrams:
Your problem is as stated above, you need to connect the grounds together. Otherwise, the Arduino PWM signal has no return path (remember a voltage is always relative to something) to Arduino ground since the grounds are not connected.
It's okay to connect all the grounds together (arduino and DC supplies)
The only time is isn't is in the very rare case where you might have a supply "ground" that is above earth ground relative to supply grounds (e.g. a 20 V supply with V+ at 50V and V- at 30V relative to earth/AC ground could not be connected to a 20V supply with V+ at 20V and V- at 0V)
If in doubt you can test for any voltage between the grounds with a multimeter (e.g. one probe to one ground, one to the other ground) but since most DC supplies are floating (not referenced to earth ground) then essentially the outputs are just like batteries.
Hope I haven't confused things here :-) Connect them together and let us know how it goes. Here's an altered version of your diagram (note extra black ground lines):
From what I can see this little box is designed to take a 12V low-current signal and amplify it to a 12V high-current signal.
It is not suitable for directly connecting to an Arduino.
You will need three NPN transistors to connect between V+ and each of the R, G and B inputs, and then drive the bases of the transistors through a resistor from the Arduino.
But that's only a wild stab in the dark since there seems to be absolutely no documentation available anywhere.
After much hunting I managed to find this image:
so it seems it is designed to go midway through a chain of LEDs to power more of them, not be driven by a low voltage device like an Arduino.
Related Topic
- Electrical – Issues with NPN Transistors and RGB LEDs (Common Anode)
- Electrical – Controlling individual LED strips of different kinds and lengths with a single microcontroller
- Electrical – Controlling DC voltage with Arduino
- Electronic – arduino – Which of these is the correct wiring of an RGB light strip with n-channel MOSFET for Arduino
Best Answer
simulate this circuit – Schematic created using CircuitLab
This is a good first cut. The Arduino output is assumed to be 3.3 volts, and the total of 33 k load on it should not change that appreciably. C2 gives a turn-on/turn-off time of a millisecond or so. OA1 is a single-supply, rail-to-rail opamp. With 1 volt on the + input, it will drive enough current through Q1 to produce 1 volt across R2, which in this case will be 10 mA. You can change the LED current by changing R2. The R5/C1 network will keep noise on the 12V line from upsetting the op amp.
The opamp should not draw much current, and the Q1/R2 combination is no less efficient than a simple resistor.