An LED You Can Blow Out, With No Added Sensor

We’d seen it done with buttons, switches, gestures, capacitive touch, and IR remote, but never like this. [electron_plumber] made an LED that can be blown out like a candle, and amazingly it requires no added sensors. The project uses an Arduino to demonstrate turning a tiny LED on and off in response to being blown on, and the only components are the LED and a resistor.

[electron_plumber] used an 0402 LED and thin wires to maximize the temperature responses.
How is this done? [electron_plumber] uses an interesting property of diodes (which are the “D” in LED) to use the LED itself as a temperature sensor. A diode’s voltage drop depends on two things: the current that is being driven through the diode, and the temperature. If the current is held constant, then the forward voltage drop changes reliably in response to temperature. Turning the LED on warms it up and blowing on it cools it off, causing measurable changes in the voltage drop across the device. The change isn’t much — only a handful of millivolts — but the effect is consistent and can be measured. This is a principle [Elliot Williams] recently covered in depth: using diodes as temperature sensors.

It’s a clever demo with a two important details to make it work. The first is the LED itself; [electron_plumber] uses a tiny 0402 LED that is mounted on two wires in order to maximize the temperature change caused by blowing on it. The second is the method for detecting changes of only a few millivolts more reliably. By oversampling the Arduino’s ADC, an effectively higher resolution is obtained without adding any hardware or altering the voltage reference. Instead of reading the ADC once, the code reads the ADC 256 times and sums the readings. By working with the larger number, cumulative changes that would not register reliably on a single read can be captured and acted upon. More details are available from [electron_plumber]’s GitHub repository for LEDs as Sensors.

Embedded below is a video that is as wonderful as it is brief. It demonstrates the project in action, takes a “show, don’t tell” approach, and is no longer than it needs to be.

In the past we have seen LEDs that can be blown out like candles in different ways; one used a microphone to detect blowing while another used a thermistor to detect the temperature change from blowing. [electron_plumber]’s project is notable not only for using no added parts, but also for being documented in a way that just about anyone can get up and running, and that’s something we always like to see.

40 thoughts on “An LED You Can Blow Out, With No Added Sensor

    1. For sure, a property generally buried or obfuscated now and then. With addition of one or two (minor) components offers the base for some ‘out there’ instrumentation applications, in that case with a uP to map the overall multi-variable calibration all too easily.Thanks for post :-)

    1. Yes, smaller diode (0402) also works better (low thermal mass), mounting it on pcb would work worse (pcb would be a heatsink). Even using thin wires helps (they act like a heatsink too).

    1. It actually depends on where you’re from! If you speak each letter individually (sounds like “ell-ee-dee”) like we do in the USA, then “an” is correct because it precedes a vowel sound. If you treat the initials as an acronym (sounds like “lead” the element), like I’ve heard aussie Dave Jones say in his EEVBlog videos, then “a” is also correct.

      It’s unfortunate for technical writers because, unless you know it’s a regional thing, it just looks like incorrect grammar.

    2. What? LED pronounced like lead vs LED spoken as L.E.D. is a regional thing? Really?

      I’d heard and used both myself and never made that connection that it was a regional variation. For a moment I thought… oh… I just learned something new… but now that I think more about it… I am very skeptical.

      How does a spelling or pronunciation become THE correct one normally? At first, with a new word it’s basically a free-for-all. Then the employees of some dictionary that the people on one side of the pond or the other respect as authoritative say it is so. And it is only correct because enough people agree to follow that authority.

      What authoritative dictionary tells of the proper way to pronounce the abbreviation for “light emitting diode”?

      So… I guess it’s just a question of most common usage then? Well.. if people in the US and Britain came up with usages on each side that were common enough to be considered the correct usage for that area how did that happen? How do most of us learn these things in the first place? In the old days, pre internet that would be in a book. How many books tell one how to pronounce LED? Sure, eventually they might talk to one another and start to converge on pronunciation but what percentage of the population was that technical pre-internet? I would expect thousands of pockets of people in the US and hundreds in Britain with some pockets saying ‘lead’ and some saying ‘L.E.D.’ on both sides of the ocean.

      Unless this consensus developed very recently, now in the Internet days. But then.. why would it be different in the US and Britain? We all share the same YouTube!

      Nope. I bet both get used quite a bit on both sides of the ocean and some people just assumed that since some English speakers talk like themselves and others use the opposite it must be a US vs UK thing.

      1. It seems to be a form of speciation. One you have sufficient population for one pronunciation it sticks. I’ve seen this personally where my American office has enough Australians that they all say aluminium and incoming Americans switch to match the local jargon.
        Personally I prefer led to l.e.d. because if I’m going to make the effort to say all the letters I may as well say light emitting diode, which is only 33% more syllables. (See also www)

    1. Suffice to say you can turn the LED on long enough to measure or via alternate at lower volts if you prefer so you can’t see the light one bit…

      Reminds me, we did tests on LED vs 5ns detectors in respect of shortest period of time to detect LED turn on with fastest photosensor few years ago – part of a project to attach measurement to determine turbocharger turbine speed on a T3 with the RB30 engine on this car, great fun, top speed 240Km/Hr and didnt take long to get there either… ie. We detected each edge as it spun to approx 130Krpm – which happens to be same as my oldie Beckman ultracentrifuge – hey I want another one for parts – msg me through quora link !

      1. Just a tip lately there’s been many plates copied off of the net from car sales sites and gumtree leaving the plate on the image lets them do it, They will use it for robberies and Toll evasion and other purposes that will cause months of grief you they will spray their cars etc just to do this.

          1. Thieves are getting lazy these days – they cant even be bothered to get off their chair and cruise around town looking for a similar model/year/color car? Maybe my car is just popular for the region I’m in, but Id say I cross paths with another 4Runner of same generation & color at least once every 2 mins driving around town, whether the other car is driving or parked.

        1. Yes Dave Davidson.
          In normal circumstances most appropriate to alert and thanks for thinking of the issue from the perspective of its abuse by criminals. In general a pertinent issue and substantive if you were in Australia as its a Western Australian license plate and these days many police cars Australia wide have non-obvious automated scanning equipment with good bandwidth to the databases, easy to spot as those traffic sedans have three antennas…
          There is an online nationwide verification in Australia, not sure about USA…
          https://online.transport.wa.gov.au/webExternal/registration/

          BTW: Your name link goes to a facebook page with error msg
          “The link you followed may have expired, or the Page may only be visible to an audience that you aren’t in.”
          Feel free to msg me via my quora profile link on my name on this comment (I changed it from earlier comment) and I can tell you more ;-)

  1. Wow… Insanely cool project!
    I guess, next steps will be adding some more precise temperature measurement (i.e. TMP411 from TI), so the resolution is even higher…
    And then it’s possible not only to blow out LED, but also implement flickering, like in real candle!

  2. Awesome hack! Would not have guessed this to work *that* nicely! – I just copied it with a red 0603 LED soldered to some 10 cm long, 0.1 mm diam. copper wire and using a 220 Ohm series resistor. Works like a charm.
    Also tried some 3 mm LED: this needed *a lot* of blowing and worked better with a larger sampling buffer, which seems natural given the larger thermal mass.

  3. If you have a project that has an always on status LED you could use that trick to give it a sense of solar time as the environment cycles through hot and cold over the day. This may even work in an air conditioned environment as they do vary a bit. Would be interesting to see if it was accurate enough to compensate for drift in the CPU clock and replace a RTC in some applications. Track the behavior of such an LED over years and you’d have enough data to extract the various frequencies out of it, or you could just guess based on first principles and some smart mathematics.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.