circuit board advice and programming questions

I’m making a 2 part board for an led unit that operates at 12-24VDC and will produce MINIMAL EMI for radio communications. the board is going to have to take in power and a communication input and then daisy chain the power and the rest of the communications. example led 1,2,3,4,5 are connected together one into the other. but each one needs to be able to work interdependently of another where unit one is flashing mode 1, unit 2-4 is in mode 2 and unit 5 in mode 3 and on and on up to ten units long. likewise, the units stack tall up to 4 units tall but only ever in 2 modes (ex: 4 units high but unit 1-2 are in mode one, and unit 3-4 are in mode two.)

when it comes down to it i need 5 modes per unit. just worrying about each unit it will have 9x 3w led’s that operate at 3-4v each @ 1A an led so 3 x 3 led’s for close to 12VDC each string of 3 and that would only make 3A per unit required. my concern is how wide the trace will need to be and weather i can daisy-chain up to 10 units wide though the unit. (each unit physically connects together with a pin and pad design)

I’m planning on using one board with the led’s on one side, the power control unit and the connectors for connecting to power(XT-60) and I/O (RJ45/ 8P8C) and to connect two units by wire and two led displays to show the mode on the other. I have attached a picture of the led’s and the sketch i have designed.

in summery:
daisy-chainability
power requirements
amperage control
MINIMAL EMI
display to led 8 seg disp.

cminke: I'm making a 2 part board for an led unit that operates at 12-24VDC and will produce MINIMAL EMI for radio communications.

How minimal do you need your electomagnetic interference to be? Any specifics?

cminke: communication input and then daisy chain the power and the rest of the communications.

Well, daisy chaining the power is easy enough, BUT from the drawing, it looks like you are trying to daisy chain AC. While this is a valid technique, it would save time and money to have the "master" unit to do AC to DC conversion (lets say 110VRMS to 12VDC) and then have the "master unit supply 12VDC to all of the "slave" units (in parallel). As for daisy chaining communications, you might find it difficult and/or unnecessary. For instance, you can't "daisy chain" USB, UART, or other such serial comms. You might be able to get away with using SPI or I2C (might - depends on the distance between the units). If you really want to daisy chain comms, I would have the "master" unit take in data from USB, then send the info via I2C to the respective "slave" units. Honestly, though, you might want to consider using switches on each unit to specify which mode you want the lights to blink in. Much simpler.

cminke: when it comes down to it i need 5 modes per unit. just worrying about each unit it will have 9x 3w led's that operate at 3-4v each @ 1A an led so 3 x 3 led's for close to 12VDC each string of 3 and that would only make 3A per unit required. my concern is how wide the trace will need to be and weather i can daisy-chain up to 10 units wide though the unit. (each unit physically connects together with a pin and pad design)

I think you need to review circuit theory again. 12 LEDs with each rated at 5V at 1A will require a 5V voltage source supplying up to 12A (total unit power = 5V*12A = 60Watts). Reason: the LEDs should be in parallel. Also, you will need relays to drive the LEDs since neither the 5V supply pin or digital I/O pins can source 12A of current. Also, don't forget the current limiting power resistors you will need for each LED. Current limiting resistor = (5V - 0.7V)/1A = 4.3 Ohm resistor rated at 5Watts.

cminke: amperage control

What amperage do you want to control?

Hi,

I’m making a 2 part board for an led unit that operates at 12-24VDC and will produce MINIMAL EMI for radio communications.
the board is going to have to take in power and a communication input and then daisy chain the power and the rest of the communications.
example led 1,2,3,4,5 are connected together one into the other.
but each one needs to be able to work interdependently of another
where unit one is flashing mode 1, unit 2-4 is in mode 2 and unit 5 in mode 3 and on and on up to ten units long.

likewise, the units stack tall up to 4 units tall but only ever in 2 modes (ex: 4 units high but unit 1-2 are in mode one, and unit 3-4 are in mode two.)

when it comes down to it i need 5 modes per unit.
just worrying about each unit it will have 9x 3w led’s that operate at 3-4v each @ 1A an led
so 3 x 3 led’s for close to 12VDC each string of 3 and that would only make 3A per unit required.

my concern is how wide the trace will need to be and weather i can daisy-chain up to 10 units wide though the unit. (each unit physically connects together with a pin and pad design)

I’m planning on using one board with the led’s on one side, the power control unit and the connectors for connecting to power(XT-60) and I/O (RJ45/ 8P8C) and to connect two units by wire and two led displays to show the mode on the other.
I have attached a picture of the led’s and the sketch i have designed.

Sorry, but trying to clarify what you want.
for example;

led 1,2,3,4,5 are connected together one into the other.
but each one needs to be able to work interdependently of another

You want all 5 LEDs to be independent of each other, but the controller can make them all or some work together?

The picture has no labels telling us what we are looking at.
Are you talking about LIGHT BOXES, like Close Encounters?

Tom… :slight_smile:

Thank you for both of your replies just to clarify a couple things the units are working off of 12 volts DC not AC second of all each unit needs to be able to be programmed and function independently of another they need to be able to the programmable through five different colors are there 5 color LEDs a piece. I will definitely take your advice on using the i2c protocol for data transfer if you believe that this will be able to work as a master to slave operation. Also I don't understand your math based on the 9 LEDs per unit if each LED is running at 4 volts then I in theory should be able to wire 3 in series x 3 rows in parallel for an added amperage of 3 amps x 12 volts correct me if I'm wrong. Also I planned on using a mosfet to switch the colors of the LEDs as all 9 LEDs will change at the same time in each unit I would like to be able to have each LED turn on independently on one color only one at a time like a mini traffic advisor in each unit

cminke:
Also I don’t understand your math based on the 9 LEDs per unit if each LED is running at 4 volts then I in theory should be able to wire 3 in series x 3 rows in parallel for an added amperage of 3 amps x 12 volts correct me if I’m wrong.

Wait, why aren’t all the LEDs in parallel? You can control all of them independently if you do.

right but wouldn't that make a massive amount of current draw if its 1A an led and 9 leds per unit remember im trying to send power THOUGH a unit into another up to 10 times (10 units thats up to 90A@4V) is that too much power to send via pad and pin contact design?

cminke: right but wouldn't that make a massive amount of current draw if its 1A an led and 9 leds per unit remember im trying to send power THOUGH a unit into another up to 10 times (10 units thats up to 90A@4V) is that too much power to send via pad and pin contact design?

yo dawg, it's all about what sort of functionality you want, and then design around that. Do you want to control all of the LEDs independently or not? If so, you can work around the 90A@4V issue.

Hi,

Can you tell us your electronics, programming, arduino, hardware experience?

Thanks.. Tom... :)

my programming experience is minimal but i understand logic well like how to organize things and arrange them to work and flow . what i don't know are the specif commands to do things like layout and design

my electronic experience is about the same im taking a electronics course in college right now and ive always self tought myself but i have made some simple led projects with the arduino and leds.

my real question right now is, what is the MINIMAL size/surface area /awg required to send 30A@12VDC? [3x1A@12VDC (3x 4VDC@100mA) x 10units ]

i need to be able to send it though a pad and pin design so im concerned about amperage being too much

There’s two things when picking a wire size or trace width: maximum heating and voltage drop.

Heating:
Obviously, a small thin trace or wire can’t take a lot of current without heating up and glowing red hot. There’s lots of online calculators available that will help you pick a minimum wire size for any current you specify. Obviously for a PCB trace, you need to know how thick it is first - this should be specified by your board manufacturer. 1oz or 35um is considered standard for most purposes. The ‘normal range’ extends from 0.5oz to 2oz and it would be unusual to specify something outside that range.

For traces that need to carry really large amounts of current (like 30A) you can design the board with no soldermask on top of the trace. Then solder a bare copper wire along the trace. That can really improve your current capability.

General wiring, like inside the walls of a house, has some more complex rules depending on if the wire is inside a conduit or in an area where a wiring fire will be discovered easily. Aircraft wiring standards make a distinction on whether the wire is in a bundle with other wires.

Voltage drop:
This one is what catches a lot of people, including myself. A wire, any wire, has some resistance. A thick wire has less resistance than a thin one. If you are sending power a long distance (like 3m/10ft or more) then the voltage drop over that length will be significant. You may put 5V power in one end and get 3.9V out at the other end. That is significant.

To work out the voltage drop, you need to know the current and you need the resistance of the wire. Usually it’s ohms-per-100ft or something like that, so you must multiply by the length of the wire. Don’t forget the ground wire also has a voltage drop, so add that length too. Then a quick application of Ohm’s Law will give you the voltage.

You can never have zero voltage drop. Usually you end up with a compromise between voltage drop and the cost or weight of the wire.

okay well i'm looking for a mass production scale so IDK how the wire on the wire trace will fair but i MIGHT just have an actual large AWG wire inside connecting the terminals in parallel. HOWEVER i STILL need to know the minimum required PAD AND PIN size to be able to connect them. havent been able to research anything yet

also ref: EMI needs to be minimal because of proximity to sensitive radios

cminke: also ref: EMI needs to be minimal because of proximity to sensitive radios

So, what frequencies are significant? You can't just say "sensitive" without some idea of how sensitive.

VHF and UHF generally 150-500mhz

i'm looking for a mass production scale so IDK how the wire on the wire trace will fair

It would be very smart of you to get professional advice before committing to mass production.

cminke: also ref: EMI needs to be minimal because of proximity to sensitive radios

What you're doing with the LEDs shouldn't give much EMI. However, to keep EMI as small as possible, keep the traces/wiring as small/short as possible. Also, if using wire, make it twisted pair wire.

Put the whole thing inside a box made from insect screen wire mesh. You'll still be able to see the LEDS but the RF noise will be contained.

Metal mesh, not fiberglass. Connect the mesh to the Arduino Gnd as well.

Is that a serious piece of advice? Ahahah :o the unit needs to be waterproof so a mesh won't be practical. But it's an interesting idea xD also @ power Broker thanks that will definitely be a good idea!

Any other opinions on microcontroller? Trying to keep a small size while being able to be prototyped