Review of N00b Schematic for Gumball Machine LED lights

[harmeister]

Hello everyone,

I recently purchased one of those large gumball machines that has the spiral piece in the middle where the gumball can roll down. This particular machine came equipped with neon lights that were controlled by a microcontroller. But the controller is no longer functional. I would like to replace this with an arduino and various WS2818b LED's

From a functional point of view I think I have all the parts that I need and understand the voltage requirements of each of the parts. But, of course, I would like for people who know more than I do to review, if possible.

I would like to have a single power supply that will supply both the LED's and the Arduino as well.

Parts List:
1x Arduino Uno R3
1x USB cable
1x 5V 15A 75W Power supply
1x MT3608 Step-Up Adjustable DC-DC
3x 40 LED strip (2 ft long each)
1x 100 LED strip (10 ft long, will need power at both ends)
1x coin “switch”

Each LED pixel draws 0.3W. So the total power need would be a little less than 67W (220 LED's + the Arduino) if everything was on simultaneously. Since I will be having the LED's chase, that will be improbable, but it should be able to handle it. The power supply recommends an 80% max draw, which would be 60W, so the max draw of 67 would be on occasion (90%) which the supply can tolerate. I will just have to program the LED's to not all be on at the same time in that case to keep it below the 80% threshhold.

The USB cable will essentially be permanently attached, but rarely connected to a computer. The 5v power supply will supply the power to the LED strips directly, but to power the Arduino i am running it through the Step-Up converter since the barrel connector requires 7-12V. (I will target 9v, but anything above 7 is ok). This will allow me to also limit the amperage that goes into the Arduino while keeping the USB cable and the power attached (relying on the auto switching capability in the Arduino to keep both attached simultaneously, may not be wise, I know).

The schematic I have come up with is below.

From the programming side, I am good. But just to explain, the 3x 40 strips will all be doing the same thing, either chasing or a slow pulsing. I left each with it's own data connection so that should I want to I can cycle through with different patterns and colors if I want later. The 10ft one goes down the spiral and will only be on occasionally, "attract mode" essentially, but will definitely be on when the coin "switch" is triggered (put in a coin, spin the dial, get a gumball).

My questions are as follows:

• Since everything is a constant voltage, I don't need to put any resistors in, do I? The examples I have seen deal mostly with a single LED, so those are obvious, but I don't think that is necessary with a WS2818 strip.
• The voltage drop on the 10ft one is enough that I will need to put power at both ends, that should be straight forward. Anything special I should know here?
• Do I need to connect the ground from the Arduino to the LED's? I don't think so, since it is not the thing powering the strips, but just want to check.
• Questions on how step-up modules work:

1. The MT3608 Step-Up module limits the output amperage to 4A, which is way more than the Arduino needs, and if I understand the way current works it will only draw what it needs, regardless of the max. Is this correct? I don't want to fry the module since the power supply could produce 15A, but the Arduino won't draw that.
2. How much current am I going to lose by increasing the voltage or is that a non-issue (see power requirements above)?

• Is there something else that should be obvious but I am missing because this is all new to me?

[JohnRob]

Hi,

Interesting project, when your done pls post a photo

General comment, In any schematic the norm is:
Power = red lines
Ground = black lines You should follow this color code with your physical wires.

Your schematic is pretty good. Easy to read and seems logical in how the signals are drawn.

Answers:

1. Correct, no resistor. The WS2818 takes care of controlling the LEDs

2. No, nothing special I can think of.

3. YES you MUST connect the arduino ground. With no ground the commands cannot reach the WS2818. Consider trying to hammer a nail into a board and the board is not connected or on anything. Or consider a bulb with only one wire.

4. Not clear why you think you need the MT3608. I assume the round (5V POWER) is the source.

Regarding the current rating of the supply. The arduino will only draw what it needs. Again consider a light in a car. The battery will put out 400Amps+ but the bulb (or LED) only takes a portion of an amp.

5. Yes (see below)

a) Your physical wiring is important. Your schematic suggests the LED grounds and power supply grounds (and when you add in the Arduino ground) should all be at on physical spot. I.e. they should all come together at one connection. Same goes for the Vcc.

b) I would change your coin input to go from D0 to ground. And I would put a 0.1 capacitor near D0 to the board ground, for ESD and general electrical noise. You should also add a 1k to 5k resistor from D0 to +5V. This will increase the current through the coin sensor and make it less susceptible to electrical noise.

[harmeister]

The schematic maker didn't have slots to connect the barrel plug on the Arduino to the stepped up barrel plug off of the MT3608.

As for why, it may be naïveness on my part. The reason that I thought I needed to stepup the voltage was because the arduino barrel required at least 7V to be functional. I had considered having the board powered directly from the 5v pin, but I want to have the USB connection be able to be plugged in to test the lights without having to disconnect the power to do the upload of the code changes. The pin would not allow me to do that.

For the ground from the board to the LED's it's easy enough to tie in, and I honestly was uncertain. Since the Arduino ground comes in from the barrel I didn't know if I needed to have it be looped into the rest of the circuit, which is essentially providing just the data line, not the power.

I have changed the colors (and simplified for schematic purposes) the power lines. That was simply an oops moment. I knew better than that.

Finally, I do not quite understand the 5.b. response. I get the resistors and the capacitors, but don't get the wiring suggestion. Again, some sort of mental block on my part. The intent is to essentially provide an interrupt that I can detect and trigger a different routine for the LED strips. It's a toggle switch. Specifically a MULON SL-2nw5 switch (tech info included below). Essentially when the coin mech turns around it will trigger the switch with a momentary close of the circuit. The wiring from the old board is connected on the Common and the NO pins on the switch, so i had planned to use the same. If I understand correctly, 5V onto Common, and GRND and D0 off of NO (with a 1k resistor after D0 and GRND split, before the wire gets back to the Arduino), or did I get that backwards? Not sure how the capacitor fits in.

Updated Schematic

Specs for switch