basic l.e.d. wiring

Oh Master - please teach me the diff between a circuit & schematic diagram?!! [ Actually, the way I see it, a circuit diagram shows the electronic path and all components and switching etc. A wiring diagram is the "physical" depiction using "real" components etc - eg, the12volt's relay pics are wiring diagrams whereas I tend to post "circuit" diagrams.    A schematic can be anything in between (as per many of the the12volt's "circuit" pics) or involve simplified or functional "blocks". Schematics are often simplified overviews to make the overall circuit's workings to be easier to understand. (So, if a circuit diagram has a block that replaces some components (eg, filter, or signal conditioning, or control circuit), is is a schematic?) ] Maybe I should review definitions, though I find the terminology people use is inconsistent, but each may be defined in each case (or company, or paper/article, etc). But it's usually trivial as readers - we usually see what a diagram conveys - or tries to convey! - without caring what its "diagrammatic type" is called. But one tip - before any test or exam, determine what the examiners mean... Why didn't I supply a wiring diagram when they asked for a circuit diagram? (Answer - because they asked for a wiring diagram and I was unaware of their definition - not that they had one! $%#@##!!) Ooops - I digressed. The underlying point - don't get too confused or hung up on ay issue. "Accept" and file it away for now and later it may (and probably will) fall in place. And always be open to new or alternative interpretations (even your own established "facts" or methods). We are clever enough to adapt, and others are clever enough to have better or alternate and still valid solutions. Oh the pain! (LOL!) Back to your diagram... The "input" fed off the LED supply. Shouldn't that be from the brake or tail signal? If so, or could be combined into the other input's resistive divider - ie, 3 resistors. As to resistor values, I'll look at that later. We want to determine 4 states - both off (easy - 0V), tail on, brake on, and both on. Note that for each, we program in a tolerance, eg, 0V is <0.5V, 3V = (say) 2.6V to 3.4V etc. Also no capacitors in series with the voltage regulator (caps do not pass DC, hence no current with flow).    They go "across" the supply, ie, between +ve and GND. That's to smoothen the voltage (by "shunting" or conducting the noise (AC) to GND). FYI - find some good "water models" for electricity. A capacitor is like a a pipe pouring into a bucket with its outlet part way up the side. Once filled above the outlet, the varying water inlet is "smoothed" out at the output. BTW - don't take water models nor any model to the extreme. They are merely models chosen to explain certain behavior thru analogy. They do not apply universally - ie, water is not electricity and a bucket is not a cap, but that bucket model is good to picture "capacitor smoothing" in principle. Too many people take the model to be the real "target" thing. Eg - if you use the atom as a solar system model, you can be in big trouble for certain theories etc. And models change. Eg - light. Once modelled as particles (eg, ping pong balls). Later modelled as waves. Now modeled as "photons" - a "particle" that exhibits "wave-like" properties. [Ain't that interesting? Do we model electro-magnetism as photons? Light is part of the electro-magnetic band. And if you really want to fuse (bad pun) your mind - what is electricity?; what is its fundumental unit? - it must exist, WE know that! PS - I suggest you might "take this onboard", but DO NOT ponder hard on it - maybe ask the experts and see how they also squirm!] Oh dear, lots of digression... [ My [bracketed] and FYI and BTW etc test tends to be extra info. ] But apart from series capacitors and that 2nd input, - oh, and a GND for the 78L05 - your circuit, er, schem... er, diagram looks fine. (IMO it's a circuit diagram.) Input resistance values later, though the others like 150R series LED resistors, and the MOSFET resistors look fine. Well done!

Well, still waiting on parts... I see exactly what your talking about for the capacitors.. Thank You.. that would have really rained on my parade..ajm

You wrote:"Input resistance values later, though the others like 150R series LED resistors, and the MOSFET resistors look fine."

I used a resistor divider calculator, and based the values off of what I already have in hand(470R-which were purchased pre.. You) 

So for the tail light I have a 470-R1 and a 150-R2.. giving me a 2.9v-3.4v range, based on 12v-14.4v fluctuation.. I then used 470-R1 and 200-R2 for the brake.. providing 3.7v-4.52v...based on 12v-14.4v input...

I really kicked myself on the last drawing after mentioning the cap.. lol

Good Morning, btw  :)

ajm

Will this work for the MOSFET..  Digikey.com part # IRLZ14PBF-NDajm

Only a quick look, but yeah, it looks good. I'm concerned by its 200 mOhm "ON" resistance at 6A, 5V - it seems high... Let's see, 6A x 0.2R => a 1.2V drop (at 6A). That could be okay else factored in to your resistor values. But you might be running a much lower current, hence a lower voltage drop... Assume 10 strings of 20mA LEDs => 2A total. 2A x 0.2R = 0.4V drop. Essentially negligible. Mind you, that assumes a 0.2R (200mR) ON resistance - I suspect it might be higher at lower currents. But it should still be ok. BTW - the 6A @5V means with a 5V Vgs and 6A through D to D (aka Ids). The 5V Vgs should be close to your "on" voltage - ie, the PIC etc off a 5.0V supply less a bit of "output" voltage drop (which I think is only ~0.2V etc if that, though maybe 0.5V). Remember to check if 6 LEDS per string (as per your last fig) is ok. That might be too many depending on the actual LED voltage (ie, 1.7V, 2.0V. 2.2V etc @ 20mA) and the FET and resistor drop, and the range of vehicle voltage. However the normal design would be based on (say) 14.4V and then any "under-voltage" merely tolerated as a dimmer output. But as you might have seen, LED brightness does not depend much on the voltage.    

Good Evening!... or maybe Good Morning.. depending on when you catch the ZZZ's.

Okay.. so I looked a bit more and found this. http://www.digikey.com/product-detail/en/IRLZ14PBF/IRLZ14PBF-ND/811728

I slept on more research trying to better understand how the MOSFET works and I think I found what will work. What do you think?

ajm

That's the same (MOS)FET... But it should be fine as per earlier. I think of a FET (incl. MOSFET) as a voltage of ~4-5V (Vgs) fully turning on G to S up to its rated current (ie, Igs). That's for an N-channel MOSFET (equiv to an NPN transistor) - a P-ch (equiv to a PNP tranny) requires Vg to be 4-5V BELOW S (ie, Vgs = -4 to -5V. The important things are: - enough Vgs to turn it fully on (or near fully on); - that Igs handles the current - that Igs x Vgs (ie, Watts dissipated) does not exceed its power handling. If it does, add a heatsink. Vgs below "Vgs On" means it's not fully on, but that doesn't interest us since we are simply using it as a "switch". (Varying the Vgs voltage on a FET is like varying the Ib or Ibe (Base current) on a transistor - it varies the current thru its "heavy" path, ie, Igs, or Ice for a transistor. IOW they can be used as amplifiers - ie, the much larger output current is proportional to the input voltage or current respectively.    Many describe a FET as being a "voltage controlled transistor" noting that a transistor is controlled by its (Base) current, though there are certain important differences (eg, a transistor output is a PN junction whereas a FET is more like a resistor - it's either an N "channel" or a P channel (it does not cross thru a P or N segment). IMO FETs are easier to use as it's merely a voltage to its Gate (at negligible current - ie, nA or uA) whereas a transistor requires "the correct (Base) current" (typically mA). Generally you design transistor circuits "backwards" - ie, we want 200mA output for a transistor with a minimum gain of 50, hence the base current should be 200mA/50 = 4mA. If the resistor in series with the Base is too small, the Base current might be too high and blow the Base. For low voltage, FETs don't care. Since their input impedance/resistance is typically Giga-Ohms, the "base" (gate) current is only nano-Amps. But web pages can explain that better than I have. PS - good night. It's nearly 1AM here, and under 6 hours till my alarm goes off.

I understand that it will work.....but I found another one.. wondering if you think this will be more suitable... Yes or No.. hehe  :-)

http://www.mouser.com/ProductDetail/International-Rectifier/IRLU3410PBF/?qs=9%252bKlkBgLFf09xnqw0semuw%3d%3d

ajm

No, Vgs 10V - you only have 5V. Plus harder to heatsink if needed (designed to solder its "back" to the PCB)

Thank You.  I just started looking at the basic commands.. Another learning curve ... but I will make it eventually..ajm