Didier Stevens

Sunday 3 April 2022

Power Consumption Of A Philips Hue lamp In Off State

Filed under: Hardware,technology — Didier Stevens @ 17:25

A Philips Hue lamp is a LED lamp that can be controlled wirelessly. It always draws power for its control circuitry, also when the LED is turned off.

I wondered how much power it consumes in the off state. Doing some research, I found a couple of forums where people asked the same question, and getting answers that is was very little, varying from 0,01 A to 0,02 A.

I got similar results for the current when I measured this:

Figure 1: Switched off Philips Hue drawing 0,0175 A (varying easily with 25%)

But I wanted a more precise answer, and not only the current. I am more interested in the power (Watt) consumption. As our domestic electricity meters measure real power over a period of time.

Thus I measured the power consumption of a 1100 Lumen color Philips Hue lamp that I had switched of via the smartphone app over a period of 10 days.

Figure 2: Test setup

And these are the numbers I got after 10 days:

Figure 3: After 10 days of operation in the off state

0,07756 kWh over a period of 10 days, that’s 0,32316 W. Notice that the display indicates KWh, but that should be kWh (lowercase k for kilo).

Extrapolating to a whole year, that’s 2,831 kWh. Which in my case, correspond to a cost of €1,50 (roughly speaking) per lamp per year.

With online numbers claiming the current to be between 0,01 A and 0,02 A, at first I expected the power consumption to be higher. But the power factor is quite low (around 0,10), explaining a lower power consumption.

Monday 9 November 2020

The Qwerty Effect And Passwords

Filed under: technology — Didier Stevens @ 0:00

I recently learned about the Qwerty effect on a podcast: baby names are more likely to contain characters (percentual) from the right hand on a Qwerty keyboard than characters from the left hand.

This got me wondering: what about passwords?

I wrote a Python program and let it run on the rockyou password list:

There is a qwerty effect in this list: 57% of the passwords have more letters from the right-side, and 43% from the left-side.

To decide if a password is “left” or “right”, I count the letters per password (I ignore all other characters), and if the ratio of “left” letters to the total amount of letters is higher than the ratio of “right” letters to the total amount of letters, then the password is “left”. And vice versa.

Remark that I don’t know if these passwords were created by users with a qwerty keyboard. It could be another layout. But for some layouts, the set of left and right letters doesn’t change, as with azerty for example.

 

Saturday 4 April 2020

Video: GNU Radio Companion: Acoustic Beats

Filed under: technology,video — Didier Stevens @ 13:39

In this video, I use GNU Radio Companion (without SDR) to illustrate the acoustic beat phenomenon.

I mention a 400Hz dial tone in this video, but this will vary by country.

Tuesday 13 June 2006

A Ring Tone That I Cannot Hear

Filed under: technology — Didier Stevens @ 17:10

Teenagers have a new ring tone that adults cannot hear, because the frequency is too high: 17 kHz.

Test it with Audacity:

File / New

Generate / Tone… Frequency: 17000

Play it.

I cannot hear it. But I can hear a 14 kHz tone.

The ring tones are appearing on the net: here and here.

Analyzing the first one with Audacity (Analyze / Plot Spectrum) reveals a peak at 15 kHz.

Keep this in mind when testing:

  1. your hardware (sound card, speakers, …) must be able to handle the frequency (20 kHz is a common limit)
  2. when exporting as mp3, select the right sampling frequencies (Nyquist)

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