Voltage-Current Data

The various nOOd products do not have detailed datasheets available. Ideally, such a datasheet would include a curve showing a given nOOd's voltage-current behavior, which would be different for each color, length, etc. Therefore, we acquired this data via a very simple process using a bench power supply. There was no attempt made to control or monitor the LED junction temperature. 

The test setup and process was as follows:

Here is a zip file containing the resulting data:

There is a CSV file for each nOOd named after its PID (product ID). Each file contains the voltage-current data collected. There are also plots of the data along with the Python files used generated the plots via matplotlib. Those plots are also shown below.

Single Ended nOOds

These are all 3V voltage level and come in 25mm and 128mm lengths.

Double Ended nOOds

These come in 3V, 12V, and 24V voltage levels and in various lengths.

Powering Basics

An inline current-limiting resistor is recommended. For any given power supply, the voltage-current data above can be used to determine a resistor value. Checkout the All About LEDs guide for more information about how to make this calculation.

Here's the basic equation that can be used to estimate the resistor value:

where:

• R = the current limiting resistor value
• Vs = supply voltage (i.e., whatever power supply you are using)
• Vf = LED forward voltage
• I = current flow through LED

The general approach is to pick a desired current (I) flow through the LED (up to Imax). Then use the voltage-current data to determine what forward voltage (Vf) corresponds to that current. You should know your supply voltage (Vs) for your given setup. Then value for the current limiting resistor (R) can then be calculated.

Resistor Power Rating

The current limiting resistor must also be rated to handle the amount of current that will pass thought it. This is determined by computing the resulting power (watts) that the resistor will dissipate: 

where:

• P = the resulting power in watts
• I = the current flowing through the resistor in amps
• R = the resistor resistance in ohms

Most common through hole resistors are 0.25W rated. Those should be fine for the 3V nOOds. However, for the 12V and 24V nOOds, a higher power rating may be needed.

In general, it's best to match the power supply voltage to the LED forward voltage as closely as possible. Otherwise, an excessive amount of power must be absorbed by the current limiting resistor.

One Resistor to Limit Them All

Picking some nominal LED values and computing the resulting current limiting resistor with some typical power scenarios results in the following rough estimates:

The resulting resistors value are pretty small. Note that these are the minimum resistor values. It's always OK to use a larger resistor value. 

More current means more brightness, but nOOds are surprisingly bright even when run below their maximum current. Therefore, a 50 Ohm 1/4 watt resistor can be used as a single "should just work" resistor value for all of the above scenarios.

Options for 3V nOOds

The 3V nOOds can be powered directly off a 3V coin cell such as a CR2032. This won’t be as bright as with a “proper” power source, but for small items and props it’s a great effect and runs for hours…sometimes even a couple days! Because these cells are inherently current-limited, no resistor is needed.

The 3V nOOds can be powered and controlled from microcontroller output pins via digitalio (CircuitPython) or digitalWrite (Arduino), and the brightness modulated and animated using pulse-width modulation (PWM) via pwmio (CircuitPython) or analogWrite (Arduino). Here are some things to be aware of:

• Though most microcontroller GPIO pins are inherently current-limited, it’s considered prudent to add a current-limiting resistor (as described above) so the chip isn’t continually “redlined.”
• Every microcontroller has different current drive capabilities, with limits per pin, per port, and in total. This information will usually be in the “Electrical Specifications” section of the chip datasheet.
• Some microcontrollers can sink more current than they can source. That is, you might control more and/or brighter nOOds by connecting the cathode (–) end to GPIO pins, and the anode (+) to the microcontroller’s voltage, and use inverted logic. Again, check the chip datasheet.
• Avoid using analogio (CircuitPython) or analogWrite() (Arduino) to DAC-capable pins (true analog voltage out, not PWM, such as on the SAMD21 A0 pin); LEDs require current control, not voltage control.

nOOds could also be controlled with a WS2811 driver IC — the same logic that’s inside NeoPixels! This does not make the nOOd per-LED addressable*, but…with three nOOds side-by-side (red, green, blue)…could allow for a sort of color-controllable Neo-nOOd. The WS2811 is a “sink” driver, so the cathode end of each nOOd connects to the IC. The chip provides its own current control (18mA), resistors aren’t needed.

* The highest density addressable item Adafruit carries is this half-meter NeoPixel strip, but it’s much wider and not as flexy as nOOds; not really the same thing.

Chaining nOOds

nOOds can be connected in series (end-to-end) with a corresponding increase in voltage, e.g. 3V for one nOOd, 6V for two, 9V for three and so forth. You’ll still want a current-limiting resistor. Lower voltages might suffice, e.g. two red nOOds might work from a 5V supply…you’ll have to experiment. Probably best and easiest to work with these as parallel, not serial, components.