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Topic: Resistors with LED strip (Read 306 times) previous topic - next topic

Mkstrawn

Good day folks,

I'm extremely novice and this is my first project.

5V 2812B - 8 LED pixels - chase sequence
Driver: ATTINY85 programmed by Arduino UNO
Power: (2) 3V lithium 123 batteries

2812B has the following connections: 5V, Ground, Clock.

Before I move the project from breadboard to PCB, do I need to add any resistors to this project? And if so, where would I run it/them?

I appreciate your time,
Mike

larryd

No technical PMs.
If you are asked a question, please respond with an answer.
If you are asked for more information, please supply it.
If you need clarification, ask for help.

Paul__B

The resistor is not necessary if
  • The LED strip is connected directly to the Arduino and
  • The LED strip is connected to the same 5 V power supply as the Arduino at the "5V" pin.

Note that the diagram above is misleading!  :smiley-eek:

It incorrectly shows the black (ground) wire going from the power supply connector to the Arduino.

The ground (black) wire must run together with the green (data in) wire from the Arduino to the LED strip.

Similarly the capacitor must connect directly at the LED strip and the resistor should be located there at the LED strip rather than anywhere else.

PaulRB

#3
Jul 21, 2019, 10:50 am Last Edit: Jul 21, 2019, 10:54 am by PaulRB
Quote
Power: (2) 3V lithium 123 batteries
Not sure that's a good choice. According to the ws2812b data sheet, the supply voltage should be 3.5~5.3V. If your batteries are in series, the voltage will be too high. If in parallel, the voltage will be too low. The voltage range for the tiny85 is 2.7-5.5V, so the batteries in series will be too high for the MCU also.

A better choice would be a li-ion battery such as 18650 size, because it's rechargeable and because it's voltage is nominally 3.7V (4.2V fully charged and down to about 2.8-3.2V discharged).

Another better option would be 3xAA NiMh rechargeables.

Mkstrawn

Awesome! Thank you for your help folks. I'll have to look around at my battery options.

Mkstrawn

Not sure that's a good choice. According to the ws2812b data sheet, the supply voltage should be 3.5~5.3V. If your batteries are in series, the voltage will be too high. If in parallel, the voltage will be too low. The voltage range for the tiny85 is 2.7-5.5V, so the batteries in series will be too high for the MCU also.

A better choice would be a li-ion battery such as 18650 size, because it's rechargeable and because it's voltage is nominally 3.7V (4.2V fully charged and down to about 2.8-3.2V discharged).

Another better option would be 3xAA NiMh rechargeables.
This is a project I am looking to produce, so disposable batteries are definitely the goal here. What is your opinion on running the (2) 3V's in sequence with a diode, such as the 1n4004?

Thanks!

Mkstrawn

The resistor is not necessary if
  • The LED strip is connected directly to the Arduino and
  • The LED strip is connected to the same 5 V power supply as the Arduino at the "5V" pin.

Note that the diagram above is misleading:smiley-eek:

It incorrectly shows the black (ground) wire going from the power supply connector to the Arduino.

The ground (black) wire must run together with the green (data in) wire from the Arduino to the LED strip.

Similarly the capacitor must connect directly at the LED strip and the resistor should be located there at the LED strip rather than anywhere else.

Thanks for the help! So the Arduino is only being used to program the ATTINY85. The LED strip will then be running off of a PCB with the ATTINY85 driving it. The goal is to run (2) lithium 3V batteries, but I need to find a way to reduce the voltage from 6V down to 5V, as PaulRB kindly pointed out. So I guess I'm trying to figure out what other Diodes, capacitors, regulators, etc. I need to include in my schematics.

If my lingo is off I am sorry hahaha I am brand new to this. But you folks are making it much more fun and easy for me!

Thanks again.
Mike

larryd

You can use a buck converter to go from 6v to 5v, lots on eBay.

A dirty way way is to add a silicon diode (.7 volt drop). You will need to watch load currents.

6v - .7 = 5.3v



No technical PMs.
If you are asked a question, please respond with an answer.
If you are asked for more information, please supply it.
If you need clarification, ask for help.

PaulRB

This is a project I am looking to produce, so disposable batteries are definitely the goal here. What is your opinion on running the (2) 3V's in sequence with a diode, such as the 1n4004
This is 2019 and the planet is in serious trouble because of the way we humans treat it like a giant trash can. No-one should be promoting disposable batteries in my opinion.

Mkstrawn

You can use a buck converter to go from 6v to 5v, lots on eBay.

A dirty way way is to add a silicon diode (.7 volt drop). You will need to watch load currents.

6v - .7 = 5.3v




Very cool! Thanks Larry, I'll look into it.

Mkstrawn

This is 2019 and the planet is in serious trouble because of the way we humans treat it like a giant trash can. No-one should be promoting disposable batteries in my opinion.
I hear ya. Well I'll do some more research on rechargeable batteries. Right now my goal is to get 5 prototypes done for as little cost as possible. From there, I plan on finding an engineer to help me get the electronics dialed in before I start producing more of them, so I'll definitely inquire on rechargeable options once that happens.

Thanks again for your help, Paul.

Mike

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