science fair project help?

Thread Starter

dhawkins263

Joined Feb 1, 2018
13
ok in my school there is a science fair coming up and i was originally going to do a marx generator like what i had posted in a recent thread. but before i decide I want to know if anyone can give me any ideas on a science fair project that has to do with electronics? :)
 

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wayneh

Joined Sep 9, 2010
17,143
If your goal is to win, think about the judges and what they will be looking for. Read the fair's published comments regarding the goals and judging criteria. Give your audience what they want.

If you just want to have fun, figure out what interests you and go for it. Just be prepared to accept that the judges may not care for it.
 

ebp

Joined Feb 8, 2018
2,332
I have no idea of your capabilities and what you might be able to get for instrumentation, but here's one:

LED lighting is becoming very popular. Depending on the circuit used to drive LED lamps for AC power, the light output will vary from constant at a particular level to rapidly changing from a low level to a high level, usually at a frequency of twice the power line frequency. Most people cannot perceive this "flicker" because it is above "flicker fusion frequency" for humans. Some people claim they can perceive it and that it causes them headaches and other ills.

Project: actually measure the brightness ripple (variation in brightness with time, where the time interval of interest is one cycle of the AC power line) of several different LED lamps, including those that can be (and are being) dimmed. This does require an oscilloscope and some special circuitry (light meter that responds fast enough) and doing things with AC power.

If you can identify some LED lamps that do have large brightness ripple and some that don't, test some people to see if they can perceive the ripple. If you do a "double blind" test you'll totally impress the judges, assuming they know about that sort of thing. Double blind testing does require helpers to do the testing because neither the helper nor the test subject can know which lamp is which. The aim of double blind testing is to reduce the possibility of someone falsely perceiving something to be the way they believe it to be. Same for the people who administer the tests - if they know which is which they may "give it away" to the test subjects.
Double blind testing is real science. Testing of many things, such as drugs, is done this way.

Some people may not like the term "double blind" when you are testing something to do with vision ;)
 

Thread Starter

dhawkins263

Joined Feb 1, 2018
13
regarding ebp's post about LED lamps and double blind, seriously this sounds really cool:D.
all i have to do is get a hold of an oscilloscope. thanks for the feed back
 

Alec_t

Joined Sep 17, 2013
12,000
..... but don't try powering LEDs directly from the mains: that can be extremely DANGEROUS. Use a step-down transformer (not a switch-mode adapter/supply) to get a lower voltage if you want to test/demonstrate something to do with ripple.
 

ebp

Joined Feb 8, 2018
2,332
To clarify - I am talking about commercial LED light bulbs that you would use to replace a line-operated incandescent light bulb. Some are dimmable, some are not. Some have driver circuits (quite complex electronics) inside that apply almost pure, smooth DC to be actual LEDs. Some have circuits in which the LED current and instantaneous brightness follow the instantaneous AC voltage (the LED lamps that have what look like fat yellow filament in them are like this).

There is another way to get some idea in general terms of whether the brightness is constant. One word only (so TS will think about it): stroboscope
 

philba

Joined Aug 17, 2017
960
What ever you do, remember that the judges tend not appreciate the truly scientific work but rather the visual impact of the display. So, go for serious crowd-pleasers.

A cynical professor's advice about teaching seems to apply here: If you make them think they are thinking, they will love you but if you actually make them think, they will hate you.
 
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