Well project Flashy lights got another step closer as I found Autodesk 123D Circuits that allows you to play with an Arduino without having to break it in real life. So I made up a quick mock up of the Amber Beacon project I have. The code will make the programmers twitch as I suspect its over complicated.
I did have issues trying to work out the correct way to hook up a MOSFAT transistor and I am using bulbs as the LEDs I plan to use are going to be 10W LED and wanted to simulate that better.
Now to work out how to have multiple patterns, make it switchable, and possibly to include some PWM (Pulse Width Modulation) AKA brightness adjustment.
I know this is complicated way to build something I can buy off the shelf but it does mean I get to play. Eventually the Amber Beacon on top of the vehicle will get the same upgrade with better (synced) flashing. Even thought of hooking the amber bar to the indicators so when the Alarm goes off so does the beacons, and or indication (suitably dimmed).
So a few more of my friends have chimed in with some suggestions,
Using a microcontroller is complete overkill! smile emoticon You can do non-programmable flashing with a simple timer circuit like a NE555, there are plenty of example circuits on the web. Beware your calculations of power - 12V is nominal, it can be much higher when the battery is being charged hard in cold conditions, and LEDs aren't a simple resistive device like an incandescent lamp, so whilst 0.83A is a rough average current, the peaks may be much higher, as all LED lamps are strobed at high frequency (many kilohertz) as they are much brighter that way. Transistor switching is normally done on the negative side of the load (your LED lamp) as the electronics for that is simpler than switching it on the positive side. Simplest is to use a NPN Darlington power transistor switching the negative side of the lamp, there are many transistors available from Maplin and lots of example circuits on the web. Obviously positive switching is easier to wire on a vehicle so you need to figure out which is best suited to your needs. Search for "emitter follower" or "high side switch" circuits for some ideas if you want to use positive switching. Farnell used to stock some nice high-side FETs designed for automotive use (i.e. immune to the electrical noise in a vehicle plus the heat etc). I don't recall the part numbers as it's a long time since I used any. FETs are complicated to drive unless you get the "logic level input" type that contain extra circuitry to interface directly to a signal from a microcontroller. The switching transistor will burn a fair amount of power so it will need a heat sink. It's worth getting a beefier transistor than you think you need, so that there's margin for extremes of temperature else it'll overheat and fail on a hot day.
Have you got a spec for the LEDs so we can tell if they are simply a diode or if they have any embedded driver circuit? To get the best out of any LED you need to know several things such as the maximum average power as well as the optimum over-current to drive them at. Typically you always over-drive an LED but in short bursts, as it generates far more light that way. For example if an LED wants 1 Amp average power, you could give it 1 Amp continuous and get 1 unit of light from it, but if you forced it to take 2 Amps it might give off 4 units of light, but you can only afford to turn it on at 2 Amps half the time so that the average current (power) remains the same at 1 Amp. Typically the strobing is at many kHz so that it's invisible to the eye, but the net effect is that the LED would be giving you twice as much (usually more) than its rated constant output. -Stephen Hobbs
Seems my idea of a Arduino maybe overkill but might not be as hard to work out as the wiring for the above ideas.
The LED chips I have are cheap from China and specifications are a little unknown. But below is the info I do have,
High Power chips LED COB 20mm square 10W Warm White DC9-12V 900mA 3000K-3500K 900lm 140° 10W Amber DC9-12V 900mA 585-590nm 400lm 140°
My current thinking of the layout 4 banks of 2 mounted in the grill. Not to scale mind. The chips are 20mm but have 140deg view so don't think a diffuser is needed. Might just get some clear plastic glued on unless I can find someone with a 3D printer that can print clear lenses for me. I would love to have a multitude of patterns for fun. 1 & 2 could alternate etc hence the like for the UNO which I think can deal with 8 channels.