12v LED Strobe Controller

[BobK]

Too busy right now, but retirement is coming up soon.

bob

 

[highstandardz]

Thanks for all your help. I will try to make my first module soon after the plow season. If I have issues, where would I be able to purchase a module that controls lots of leds I can install in my truck? LOL

 

[peter.s]

I've split it up into modules. Starting at the top right corner is the DC input conditioning circuit. You will need one of these to clean up the 12V supply from the vehicle, which can have interference and large surges on it, which can cause misoperation and/or damage.

The VDD and VSS arrows on the left of this module supply power to the logic ICs (in the modules at the left). Each IC must have a decoupling capacitor, 0.1 uF ceramic, connected between its VDD and VSS pins as close as possible to the IC. These are not shown on the schematic but you DO need them, to prevent glitches and incorrect operation. They are especially important in electically noisy environments, which yours is.

Hope no-one minds me resurrecting this thread.

I'm interested in the set up Kris put together - particularly the DC conditioning circuit at top right of his diagram. I'm a little confused by the set up so I'm hoping someone can elaborate on it for me? My apologies if these are basic questions...

In the conditioning circuit diagram the top +12V line drops down to a VMM and then a VDD before continuing to the other circuits suggested by Kris. What exactly does the VMM and the VDD connect to?

Also - is the RD10R a 10Kohm resistor?

And - Kris states that each IC must have a decoupling capacitor (0.1uF ceramic) connected to the VDD and VSS pins. Does this include a 555 timer if I were using one?

 

[KrisBlueNZ]

Hi Peter

In the conditioning circuit diagram the top +12V line drops down to a VMM and then a VDD before continuing to the other circuits suggested by Kris. What exactly does the VMM and the VDD connect to?

That circuit at top right is a two-stage protection circuit to protect the semiconductor circuitry from noise, spikes, and surges on the automotive supply, which is normally very electrically noisy.

The varistor is there to protect against load dump, which will occur if the battery becomes disconnected (e.g. if the battery terminals are not strongly attached and you drive over a bump), where the load on the alternator/regulator circuit disappears. This produces a surge voltage over 100V (I've seen numbers as high as 160V mentioned) for several hundred milliseconds. The varistor is supposed to absorb a lot of that energy but in the worst case it will fail; with luck, it will fail short circuit and blow a fuse upstream. (You could - and probably should - include a fuse to the right of the varistor in this circuit.)

That varistor specified has a clamping voltage of 39V but they're no longer available. Now, I recommend the Littelfuse V18AUMLA2220 which is an SMT part. It has similar specifications.

VMM is the automotive 12V rail with no further protection. It's used as the positive supply for the LED pod circuit just below it. These can't be powered from VDD because they draw significant current and this would cause voltage drop across RD. This means the LED pods may have to withstand up to 40V in worst case conditions.

There are other way to protect circuitry against surges on the automotive supply - a high-voltage switch that simply disconects the circuit on overvoltage may be suitable.

VDD is the supply voltage for the circuitry, after the second stage of protection, which consists of a series resistor, RD, 10Ω, and a 15V, 3W zener diode to 0V, with another smoothing capacitor.

Also - is the RD10R a 10Kohm resistor?

10Ω and should be rated for 5W. I should have mentioned that on the diagram!

And - Kris states that each IC must have a decoupling capacitor (0.1uF ceramic) connected to the VDD and VSS pins. Does this include a 555 timer if I were using one?

Yes, definitely - especially for a 555. The 555 generates nasty current pulses at its supply pins when the output changes state.

 

[peter.s]

I recommend the Littelfuse V18AUMLA2220 which is an SMT part.

Hi Kris - Thank you for replying so quickly and clearly! The explanation of how (and why) the protection circuit works is very helpful

Just to make sure I'm clear on the varistor - are you suggesting to replace V18ZA40 with V18AUMLA2220?

 

[KrisBlueNZ]

Yes.

 

[peter.s]

Thanks again!...

 

[peter.s]

Just to make sure I'm clear on the varistor - are you suggesting to replace V18ZA40 with V18AUMLA2220?

Hi again Kris - I'm having trouble getting hold of the varistor suggested for this set up... and I don't know enough about this to decide on an alternative.

Would you mind suggesting an alternative component? This is what I have readily available - http://www.gmelectronic.com/varistors

 

[KrisBlueNZ]

I think your best option would be http://www.gmelectronic.com/vcr20d220kar-p119-374

 

[peter.s]

Thanks again Kris, this is much appreciated!

 

[lilmatt119]

I too am planning to build a control box in the near future, so I am studying up on the circuitry, and therefore thank you Kris, for having already made that schematic.I do have a question though. Is there a way to make multiple pattern options selectable with a switch, or is that microcontroller territory?

If it is micro territory, I will just add in the knobs for the potentiometers into my box as well. If I go this route I plan to wire a switch where I can select between the strobe generator #2 and the wig-wag generator.

 

[KrisBlueNZ]

If you have a limited number of outputs, e.g. just left and right indicators, then you can generate all of the patterns independently and just use a rotary switch to choose between them. A microcontroller would make things much simpler electrically, but either way will work.

 

[lilmatt119]

that's what I was thinking. Thank you!