Newbie - Which board and other parts?

Thanks in advance to those that reply. I am very inexperiened with electronics, but with what I've read, I think I can handle this if I'm pointed in the right direction.

I'd like to experiment with an Arduino for a project I have in mind, and I would like to buy the right board without overspending. I would like to wire 7 banks of 15 LED's with each bank lighting up sequentially (one at a time, like KITT in Knight Rider).

My LED's are going to be wired/installed out away from the board in a pattern, so I don't want to connect them directly to a breadboard (unless that's the best way to wire it!).

To the point: 1) Which board can accomplish this (I don't want to buy more than I need - cost is important)

2) Is there any other board-specific hardware that I need to be sure to purchase (not talking resistors, wires or LED's, and I'm not powering anything other than 105 LED's)

Is there any other project information that would be helpful? Thank you again!

-Ryan

I would like to wire 7 banks of 15 LED's with each bank lighting up sequentially (one at a time, like KITT in Knight Rider).

Assuming it's one bank at a time, a standard Arduino (using ATMega328) would be fine. But let's say you want to be able to control the 105 LEDs individually, than you'd need a 128 bit decoder (a single 7 to 128 bit decoder is quite rare, but you can chain up multiple smaller decoders, for example 4 32bit 5 to 32 decoders) in order to be able to utilize the limited number of pins ATMega328 has.

That said, you can relax the requirement for the number of decoders required and go for a higher pin count chip (i.e. Arduino Mega), but even with Mega, you will still need to multiplex some pins since it only has 70 usable pins.

You'll also need to use some kind of LED driving circuitry since 100 plus LEDs can easily consume 1A or more current and the on-board power supply will not be able to handle that load.

I'd suggest you search this forum for Knight Rider and see what approaches other people had tried.

If you used a single decoder (or several smaller decoders acting as one) then you can only turn on one LED at a time. If thats all you wanted to do you just need 15+7 pins (connected something like this: )

Since only one LED in each bank is going to be on it could be accomplished with seven 74xx154 4-to-16 decoders (one for each bank) or you can wire it as pictured in the above and strobe each LED that you want to be on for 1/7th of the time with 7x the current. If you do this fast enough it looks like they are on constantly (this is what is often done for marquis displays).

I appreciate both of your responses. I mis-typed my number of LED’s (not sure what I was thinking) and it’s only 40 total (8 banks of 5). To some of your points:

Assuming it’s one bank at a time, a standard Arduino (using ATMega328) would be fine.

Yes, one bank at a time. I would love to wire all the LED’s to light individually, but I’m going to wire in a 75 foot straight line, and I think the sheer amount of wire would be cost-prohibitive.

You’ll also need to use some kind of LED driving circuitry since 100 plus LEDs can easily consume 1A or more current and the on-board power supply will not be able to handle that load.

If only one bank is on at a time (8 total LED’s), is power an issue?

My bigger question about power is with the distance of the last bank from the power source. If the last LED is 75 feet away, is that too long and will the power drop?

Thank you again, I appreciate it!

-Ryan

If only one bank is on at a time (8 total LED's), is power an issue?

it wouldnt be But it is always adviced to have a seperate powersupply for things which might require more power than a arduino can supply

My bigger question about power is with the distance of the last bank from the power source. If the last LED is 75 feet away, is that too long and will the power drop?

YES

OK, so will this be sufficient to address the power drop over 75 feet?

1) plan on running with additional (AC) power 2) Plan on a different resistor for the bank that's furthest away?

Or, is 75 feet insurmountable? Is Arduino not the right device?

Thanks!

OK, so will this be sufficient to address the power drop over 75 feet?

Yes

  1. plan on running with additional (AC) power

Thats a Big no both the arduino and the led’s are not designed to run on ac power !

Or, is 75 feet insurmountable? Is Arduino not the right device?

i think arduino can acheive this but there might be better options out there just wait and see some person with more experience can help you out :slight_smile:

  1. Okay, you don’t want to overspend: get an ardweeny, $10.
  2. You have 8 banks of 5 LEDs each.
  3. What do you have for a voltage source, and how many amps?

Lets assume you have them all wired in series, each LED drops 2.2V, with a 12V with a current limit resister sized for 20mA, so 56 ohm. Do the math for what you actually buy.

Then you just need a driver that can handle the 12V for you - two 7406s would do that, each can handle 6 banks.

Or, you wire the LEDs in each bank in parallel with its own current limit resister, and sink the resulting 100mA with transister per bank, so you need 8 MOSFETs such as
http://se.mouser.com/ProductDetail/NXP-Semiconductors/PSMN035-150P127/?qs=sGAEpiMZZMvKM5ialpXrmoKPBF94BAPg

See this thread also, similar is being done but for 8 LEDs/bank.
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1292349407/11#11

CR and Newbie thanks. I'm trying to build a working knowledge of electricity as I go along here. To your points:

1) So, to get the best voltage through the Arduino, I need to connect the DC power supply - 12v is the max (I think).

2) CR, the arrangement and functionality of my design would work much better if the LED's in each bank were wired in parallel. Radioshack has this LED, which I was thinking of using:

Peak emission wavelength: 660 nm Light output: 5000 mcd @ 20mA Forward voltage: 1.85V Absolute maximum ratings: Forward current (continuous): 30 mA Forward voltage: 2.5V Reverse voltage: 4V Power dissipation: 75mW

If I wire in parallel, would each LED need a different size resistor depending on it's position in the bank? (that math would be beyond me!)

3) I understand the concept of the Mouser Transitor, but not how to wire it with it's three pins. Obviously one goes to the Arduino port for it's respective bank, one goes into the individual bank it belongs to, but where does the other one go?

Again, my thanks. CR, how is the snow in Boston?

-Ryan

Ryan, Heres's a schematic showing a layout that could work for what you describe. I wouldn't normally draw it this way, but you said you were spreading the LEDs out so showed the 12V being spread out with them emanating from a common bus. I showed a mix of drivers for the LEDs coming from 12V. I'll post a 2nd schematic in a little bit showing LEDs in parallel, each needing their own current limit resister. I threw in some switches for effect. These would go to inputs with internal pullups enabled. I'm sure you have some s/w in mind that will be turning on the banks more automatically.

Just starting to flurry in the western suburbs, supposed to get 12-16-20", we'll see how it plays out. Have to rearrange the garage now so I can get the snowblower out later.

CR, Wow! Thanks for doing that!

I've spent the morning working on some diagrams. They are really more like concept-sketches. I'm probably not using the symbols all correctly, but hopefully it will help illustrate. Let me explain what my project is, and then I'll show you the diagram.

I am a youth swimming coach - have been for 15 years. I would like to make an LED chaser-string that I can submerge underwater so that my swimmers can see it while they are swimming. I will then set the LED's to light up in sequence at a desired "swimming pace" so that the kids can race the light that they see underwater.

A pool is 75 feet long. I'm going to space the LED's just under 2 feet apart. I thought to use 8 banks of 5 lights (40 LED's total) because it will use much less wire than running 40 individual circuits, and much less circuit controls.

The reason I am using 5 "tubes" is because it needs to be convenient to pull the lights out of the water and store them. A 75 foot tube isn't convenient, but five 15 foot tubes that can be connected and unplugged is much more useful.

I did this diagram with them in parallel, but I'm not committed to it.

URL to Diagram: http://tinyurl.com/2auet4u

Thanks again!

-Ryan

Ok, so more like this then. Shift registers colocated with arduino, connectorized to show break between segments. Showing 2 to start, add 6 more to make 40 lights. Could probably have the Rs on the arduino side of the connector. Then just the 6 wires & LEDs in each tube.

Not sure what I was thinking there, no reason the shift registers can't span the tubes ...