Yes another BTTF Flux Capacitor, please help, simple question.

Other Hardware LEDs and Multiplexing
1

Hi everyone!

This is my first post! Yes I'm new to all this like some of you and yes I built a Flux Capacitor from the movie Back to the future.

As you can see in the pictures, most the work is done, I am at the stage of connecting the LEDs.

Here's what I bought :
-(1) Arduino UNO R3 board ATmega328P CH340G (not received yet)
-(100) 5mm warm white LED (received)
-(100) 200ohm resistors (received)
-(2) Battery Power Cable Plug 9V DC (not received yet)
-(1) Power supply adapter 110V AC to 9V DC (received)
-(1) In-line power switch ON/OFF DC (not received yet)

And this is my objective, I think the pattern is called "chasing" lights :

I know most other FC builders have the time traveling light up sequence and all but me I simply want the "chasing" light pattern because it will be plugged and turned on 24h/7d/365d... hope that's not a problem for the board. And yes I did search this forum, but like I said all the FC builds I found were more complex than mine so I couldn't copy the codes or anything.

I also drew a sketch of the how I would hook it up, I added a couple of question on the sketch.

Thanks for any help at all, this is all new to me so please keep that in mind :-/

2

I'd go with a pair of wires to each LED, 30 AWG wirewrap wire. Drive each one from an IO pin, unless
(5V - Vf)/200 is less than 8mA if you want to drive 3 LEDs from one pin.
Vf of white LED is 3.2V? (5-3.2)/200 = 9mA x 3 = 27mA.

3

I would consider using individually addressable LEDs. You can get SK6812-based LED strip with WW/CW leds (warm and cool white in same package, instead of red/green/blue), or RGBW leds (with RGB and a white LED). The wiring might be easier (since you just need the one data line), and you could do much cooler animations if you chose to...

If you do just use discrete LEDs like you proposed above, I would wire them with the positive side tied to Vcc, and switch the low side.

You could use a small transistor (well, a MOSFET, probably) to switch the LEDs if you wanted to push each set of LEDs to it's maximum brightness (by using smaller resistors - with 3.2v drop on the LED, you'd need to drop 1.8 in the resistor, so you could go as low as 90 ohms (eg, a 91 ohm resistor, or 100 for some margin).

One resistor per group of three LEDs will work, though it's poor practice (if the LEDs aren't identical, they won't be the same brightness). It's better to have one resistor per LED.

What pin is that, by the way? I don't recognize the art... Looks pre-DMD era, though?

4

Frankly, I would take the easy way out and use a MAX7219.

One resistor to rule them all, two capacitors, three wire interface to the MCU (use a "tiny"), as much brightness as you could reasonably want.

Setting scan limit to three (note the restriction in drive current for this value), three columns of eight LEDs will be quite easy to wire, write the same pattern (byte) to each column at each animation step.

Couldn't be easier. :grinning:

5

I'm having a hard time understanding your replies, like I said I'm new to all this, I already bought the parts listed in my first post, no offense but unless what I bought won't work at all I'm not buying anything else, I'm looking to make a "Y" shaped design (see pictures) with four (4) LED bulbs on each branch, I have an Arduino Uno R3 board, 200ohm resistors.

Can I make it work with what I have? that's my first question.

Second question : How do I hook it all up and program it?

Thanks again!

6

DrAzzy:
What pin is that, by the way? I don't recognize the art... Looks pre-DMD era, though?

That's a 1978 Hit the Deck pinball, I bought it a year ago, I'm new to pinball as well, but I managed to fix some of issues it had, changed the rubbers/bulbs, waxed the deck but it still won't start :frowning:

7

In other words...

.. You'd like someone to tell you exactly what to do and how to build it.
Then, how to code it to do what it does in the movie.
:slight_smile:

Right?

Jason.

8

retrofiesta:
In other words...

.. You'd like someone to tell you exactly what to do and how to build it.
Then, how to code it to do what it does in the movie.
:slight_smile:

Right?

Jason.

I built the hole thing myself out of wood that I shaped into all the parts I needed, I didn't need any help for that part, now I'm stuck :frowning:

I did my research on this, I bought what most of the people use for the electronics on these things, so I'm not asking you guys what to buy, I just want to know how to hook it all up and make it work.

If I don't get any help here as soon as all the parts are in I will do a lot of testing until I get it right, but I'm just checking here so I can maybe save a lot of time and get some help before all the parts are in, but after all, that's what forums are for :wink:

keeping my fingers crossed.

9

Should be able to use the parts you have. Uno has 14 Digital I/O Pins and you only need 12 (4x3). Use one LED and resistor per Digital output and set three outputs (LEDs) on at once, then off and three more on, then off then... until you're back to the beginning and continue looping.

Nobody's (typically) going to write code for you. Start with the Blink sketch in the Learning section of this site and get one LED blinking, then get three blinking, then get four sets of three blinking, then play with the delay values between blinks until it looks right.

www.arduino.cc/en/Tutorial/Blink

10

Paul__B:
Frankly, I would take the easy way out and use a MAX7219.

One resistor to rule them all, two capacitors, three wire interface to the MCU (use a "tiny"), as much brightness as you could reasonably want.

Setting scan limit to three (note the restriction in drive current for this value), three columns of eight LEDs will be quite easy to wire, write the same pattern (byte) to each column at each animation step.

Couldn't be easier. :grinning:

Yes it can. Wiring up leds with a MAX7219/7221 is a total pain, particularly when not using a square matrix.
Given, it looks like only 12 leds, then
for easy, I'd use Neopixels, the 2812s packaged in individual led packages. Something like these:

The advantage is that they are simple to wire up, and you get full color and brightness control.
All from a single arduino pin.

evy74,
With an Arduino R3, you won't be able to do brightness control as the brightness will be set by the resistor.
The R3 doesn't have 12 pins with PWM for brightness control, so all you can do is on/off.

With the neopixels, you could treat each of the 3 sections as individual chains which would require 3 arduino pins. That might make things simpler if the patterns are always symmetric across each section.

Adafruit has lots of information and example code on how to use the LEDs including some chaser code to start with.

From a high level logic perspective the overall s/w will be similar regardless of whether MAX chips, Neopixels, or 12 arduino direct i/o is used.
The difference will mainly be that with direct arduino pin control you will call digitalWrite() to turn on/off an led and with the others, you will call a different API function to turn on/off, set color, brightness, etc... for each led.

Given you already have the parts coming in, i'd just give it a go with the parts you have.
Since it it is only 12 leds, it won't be that difficult to wire up.
Then just figure out how you want to sequence the LEDs and turn them on/off as needed to get the pattern you want.

--- bill