Recent content by axemaster

As a physicist doing electronics engineering for the past 4 years... this thread is pretty sad. As far as I can tell, LvW is exactly right. The main thing causing confusion here, is that he has failed to mention (or I've missed) that even supposedly "open loop" amplifiers have negative...

I agree with the above, and I'd like to add - if they don't answer your email, it really isn't personal. Most professors I know get an insane amount of emails - during a 2 hour class, one professor had over 30 emails pile up in his box. And this is normal. This is also why professors often will...

In general RF power harvesters don't work. Most wifi transmitters emit only a few watts at most. That power is spread out in a sphere around the transmitter, so at most you'll only capture <1% of the signal. Just from that you should see that charging a phone is completely non-viable (at least...

I'd like to jump in an quickly mention 2 things: 1. Relays have a finite lifetime. If you have one toggling on and off constantly, it will wear out. If it's switching a large current, it may burn out very quickly. 2. I strongly recommend that whatever you do, you test it out on a low power...

That would depend on the machine, but generally speaking they have a more gentle startup than linear regulators. So it shouldn't be an issue.

@benofer90 You might be able to use the buck converter you mentioned at: http://www.gearbest.com/development-boards/pp_140282.html?currency=USD&gclid=CNmE6OjC2McCFUWRHwodwmoEkQ It claims to be current limiting at 10A. Whether this is true or not... well, without a datasheet, who can say...

The buck converter came to mind because recently I was designing one to handle several kW... with a $2 comparator and 2 medium size MOSFETs. At 99.8% efficiency. It didn't even need a heat sink. That was the moment when I decided I like switchers. That said, switchers have the disadvantage of...

Obviously I don't know your system, but to measure RPMs you could use a few things: Encoders - This attaches to the spinning shaft. It's basically a ring with holes in it, and a light that shines through the holes. The frequency of the light flashing tells you how fast the thing is going. You...

There are a few general ways to go about this... 1. Control the speed of the generator. This is the best method, as it doesn't require dissipating huge amounts of heat. 2. Use opamp controlled transistors to control the current. The transistors will have to operate in their linear region (i.e...

If you want a useful reply you'll need to tell us more about what you're doing. What are you building, how big of a current are we talking about? What will this be used for?

The value you record will be specific to your photoresistor. Thus, there is no standard to compare it to. Ideally you would have a calibrating lamp of known brightness to set the scale. In your case, you will probably have to record the value when the full moon is out, and use that as your...

hFE is the forward current gain of the bipolar junction transistor. There should be a socket or something on your multimeter to plug in the transistor.

Very interesting, thanks for the info. I should have realized that O2, being ~20% of the atmosphere, wouldn't be significantly changed. I was also wondering how much the CO2 would increase, if you burned all the plants. The current CO2 mass in the atmosphere is 1.8*10^15 kg. I looked up plant...

I guess the part that annoyed me the most is when the Enterprise is free-falling to Earth, and the gravity inside is completely messed up and makes absolutely no sense. It was so ridiculous that it actually took me right out of the movie.

Hey guys, I'm writing a story where Earth suffers a catastrophic event, destroying all surface and ocean life. The surface is basically bathed in intense radiation. To be more specific, Earth is attacked by aliens, and ships destroyed during the battle in orbit crash into the planet below...