Output devices (week11)

Group Assignment

  • measure the power consumption of an output device

Link to Fab Academy 2020 assessment page

Measure voltage, current, resister and frequency(Hz) by the number of LEDs on NeoPixel

Using ATtiny3216 breakout board, I made a program for easier experiment that can adjust the number of LEDs in 0, 18, 36, 72, 144(max number of my NeoPixel LED is 144) by pushing switch.



I made a input/output board using ATtiny3216 breakout board as I did not have any access to lab under COVID-19 situation.

For detail about input/output board, please see individual page of output device seek

Check voltage by data pin
Check voltage by VCC pin

Then I checked voltage, current, resister and frequency.

Timelapse - checking current value by number(0, 18, 36, 72, 144) of LEDs in NeoPixel

Experiment result


  • color of LED: (255, 255, 255)
  • with 470Ω resister to data pin
# of LED1st2nd3rd
18 3.38V3.22V 3.15V
36 2.99V2.79V2.82V
72 2.67V2.54V2.58V
144 2.46V2.36V2.38V


Max Current between VCC and ground of Neo Pixel

This result is the outcome by parallel connection for the circuit of NeoPixel and multi meter between voltage and ground pin. It's not appropriate to measure the current in that circuit. Instead, I did another experiment to check current by shunt resister after I come back to lab.

# of LED1st2nd3rd
18 9.80A9.96A9.68A
36 9.03A9.40A9.24A
72 8.35A8.14A7.96A
144 6.93A6.91A7.77A


For 144 of LED in NeoPixel, the resister value is 2.12MΩ (when voltage is off).


Frequency between anode and cathode was not changed by the number of LED

# of LED1st

Check current by shunt resister as of 13 June

After I come back to lab, I could check the current by shunt resister circuit. As NeoPixel LED resister value depends on the number of LEDs and the connection, I put a resister as a serial circuit bridging 5V and GND in NeoPixel.

I tested this by ATtiny412 output board that I made for my final project.

On this circuit, I used 1Ω resister and check the voltage by multimeter.

From the formula of V(voltage) = I (current) x R (resister), I could calculate the current from voltage value that I check by multimeter.

This is a connection for the experiment.
Checked the voltage loaded in 1Ω resister for each case of the number of LEDs.



Experiment result (on output board using ATtiny412)

Firstly, I tried to blink LEDs on NeoPixel(WS2812B) with the same number(max: "144") as above experiment with ATtiny3216. However, the maximum number of LEDs that I can blink on ATtiny412 output board was "24" it looks unstable brightness.

I tried some cases as follows but could not find out the cause of this.

  • Get voltage from AC Adapter (5V) to ATtiny412 output board
    --> blinked only few LEDs(24 LEDs or less in unstable brightness)
  • Embed the same program of "tinyNeoPixel_sample_412_0613_2.ino" to ATtiny3216 breakout board,
    --> 54 LEDs by white color(255,255,255) (After change the FTDI cable as a voltage source from USB Type A connector of Raspberry Pi to MacbookPro, 144 of all the LEDs blinked successfully)
    --> 144 LEDs by green color(0,150,0)

From the experiment using ATtiny3216 breakout board, This looks to be caused by current volume flowing in NeoPixel. However, by ATtiny412 output board(v1.0), even though I change the VCC source from 5V VCC and GND pins of FTDI interface to AC Adapter(5V, 1.2A).

This also might be any electronics problems in my output board and I checked electronics continuity for each pin of Vcc, data pin to control NeoPixel and GND. THe continuity is ensured and no problem at least I could check.

For this experiment, I checked the number of LEDs by 24, 12, 6, 1 and 0

I measured the voltage for each case and calculate current (mA) by formula of I=V/R. As R=1Ω, the voltage value is equals to current in this shunt resister circuit.

# of LED1st2nd3rd
12 376mA375mA375mA
6 207mA207mA207mA
1 65.1mA65.1mA65.1mA