I have not worked with Arduino products, but they were recommended to me as the "right way" to complete my project. My project is a 3d Printed Stargate hitch receiver brake light. I modeled it as an exercise to learn Rhino3D. At any rate, when complete, it would be nice if the nine lights (LEDs) in the chevrons could chase or pulse when the brakes is pressed. The LEDs in the center ring would come on as one big light. I've drawn up what I assume would be a possible wiring diagram but I actually have no real knowledge how this it done. I'm hoping someone here could tell what items would be necessary. Maybe correct the diagram and/or recommend the correct parts?
Some of what I don't know:
Which pins for 12V power from the Auto harness?
What converter for 12v auto to Arduino power?
Which of the many Adrino models would be appropriate for my project?
Are resistors necessary for the LEDs, If so which ones.
I'm sure there are a lot more questions that I don't even know to ask.
The Arduino can usually run from the car's "12V" power through Vin or the Barrel jack. The "recommend" voltage range is 7-12V, and the limits are 6-20V.
...You'll get more than 12V with a fully-charged battery or when the engine is running and there will be some noise & voltage spikes on the power supply, so some people recommend an external switching regulator. I've got an Arduino Uno running in a vehicle with only the Arduino's on-board regulator with no problems (in my particular vehicle).
If there are any 12V input signals (tail-lights, brake lights, turn-signals, etc.) each input needs a [u]voltage divider[/u] (2 resistors), plus a pair of diodes (or a Zener diode) for [u]over-voltage and negative-voltage protection[/u]. The resistors in the voltage-divider can add-up to about 10K (it's the ratio that's important).
Are resistors necessary for the LEDs.
YES. You ALWAYS need a resistor (or other current-limiting circuit) with LEDs! Adafruit has a [u]LED tutorial[/u]. (I actually haven't read it carefully, but it looks right and I generally trust Adafruit.)
If so which ones
Most "regular" LEDs are rated for up-to 20mA. If we assume/approximate 2V across the LED and 3V across the resistor, Ohm's Law says 150 Ohms (minimum resistance for maximum current). In the reality, 220 Ohms is more common (for about 14mA).
But, there's one more issue... The TOTAL current shouldn't exceed 200mA. i.e. If you have 20 LEDs at 20mA each and they are all on at once, you're exceeding the specs.[/quote]
I'm still trying to get my head wrapped around this. But from your response I gather it can't be done. I'll have 23 LEDs x 20mA = 460mA. That is more than double the 200mA you mentioned.
KaisoBuilder:
I'm still trying to get my head wrapped around this. But from your response I gather it can't be done. I'll have 23 LEDs x 20mA = 460mA. That is more than double the 200mA you mentioned.
It's doable. Just can't power all the LEDs at the same time through the Arduino. You can "control" them though using a mosfet to handle the switching. Search YouTube for Arduino and mosfet and you'll see what I mean.
Edit - added the parts in bold to add some clarity. But my statement may not be entirely true as evidenced by the replies below.
KaisoBuilder:
I'm still trying to get my head wrapped around this. But from your response I gather it can't be done. I'll have 23 LEDs x 20mA = 460mA. That is more than double the 200mA you mentioned.
spend some more time learning how to power LED's.
how often will you have them all powered at once ?
you can light 100 leds, using one pin if you have them in series and the pin never sees more than 5 vdc and 20mA
if you chase, and never have them all on at one time, your max current is 20mA
but, if you need help with that, you must post a link to the data sheet. http://www.crossroadsfencing.com/BobuinoRev17/
has a board with a chip that does 64 individual using 4 pins.
MAX7219 daisychainable breakout board
just past half way down his page
there is a phenomenon called POV or persistence of vision. if you flash an LED the light will remain in you vision while you flash a second. this way, you can flash 5 so fast, they all appear to be on, at full brightness, but since you only have one powered at a time, you use about 50mA total current.
I just realized. I only need 9 LEDs to chase. The rest are all on. Can't those can be separate and direct from car power. And the Arduino only for the chase?
