Electrical Engineering

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2:30 AM

I'm a newbie with electrical engineering. I found out that EE might be the place to take questions about modifying Android hardware; however, much emphasis has been placed on "background research."

What kind of background research do I need to do?

In case it makes a difference, I'm trying to figure out if/how I can put a GPS locator into my $20 tablet that didn't come with one.

1 hour later…

Nick Alexeev

3:35 AM

@Shokhet Buy an external GPS receiver, although that doesn't qualify as "modifying by EE.SE" standards.

The person who have sent you to EE.SE doesn't seem like an avid EE.SE member himself. I'm not sure he knew what he was talking about when he have sent you here.

Shokhet

@NickAlexeev That should work :)

@NickAlexeev Oh? ....you should probably leave a comment, then, if this is really the wrong place to ask. Helping other users and all that.....and saving yourself from a whole bunch of off-topic questions, coming from that post.

Nick Alexeev

@Shokhet For future reference, the questions about electronics use are off-topic on EE.SE . Taking a consumer tablet and sticking a consumer GPS receiver onto it is use, not "modifying". I'll add it to that meta discussion too.

Shokhet

@NickAlexeev Good to know. Thanks for the help.

Nick Alexeev

@Shokhet No worries. Thanks for taking your concern to chat first.

Possibly, you can get your question answered in the Andriod.SE chat.

Shokhet

@NickAlexeev No problem. I find that chat is a very underused utility around SE.

@NickAlexeev Oh! That's not a bad idea.

Thanks! :)

2 hours later…

jippie

6:11 AM

morning

3 hours later…

jippie

8:56 AM

Anyone with C knowledge around?

I want to build a lookup table in (Stellaris) flash memory

but I haven't figured out yet how to define the multidimensional array that skips couple values ...

The code looks a bit like this:

// int32_t vcos[ 2001 ][ 80 ];

static const int32_t vcos[][] = {...}

vcos[  50 ][ 0 ] = 65535;
vcos[  50 ][ 1 ] = 65332;
vcos[  50 ][ 2 ] = 64728;
vcos[  50 ][ 3 ] = 63724;
vcos[  50 ][ 4 ] = 62327;
vcos[ 100 ][ 0 ] = ...
vcos[ 100 ][ 1 ] = ...

the commented out line is how it worked fine except for the fact that it moves the array to RAM (which won't fit).

The static line should be the solution according to Google

But how do I get the specific values in the static const array? Skipping 0..49, 51..99, ... etc.

jippie

9:51 AM

Solved it by removing all empty values from the table.

2 hours later…

PeterJ

11:31 AM

@jippie, interesting to know the latter works what did you mean by removing empty values, making the array dimensions smaller? While I could see how it could for a static I didn't think most compilers would be smart enough to optmise and compact the array otherwise. P.S. guessing from the values couldn't it be a uint16_t to halve the size?

jippie

@PeterJ cos is short for cosine, it tends to go negative every once in a while ;o)

trying to do integer DFT

I'd hoped the compiler would be able to optimize unused values from the table.

@PeterJ oh and I use 32 bit mcu and was hoping to increase accuracy in due time by increasing the number of bits used for values < 1.

PeterJ

@jippie, fair enough but you need 17 bits? Otherwise thought it might make sense to use the full range of an int32 or otherwise use an int16.

jippie

I hope to calculate dft from 40(ish) samples well within 20 ms

@PeterJ I do have 256kB flash ... Not sure if retrieving 16 bits from flash is as fast as 32-bits.

Does using a zener like this actually make a difference?

Q: Zener Diode Selection for Relay

I am using a Zener diode along with a flyback diode with a relay in order to speed it up a bit. This works very well but I am currently using a rather over-sized zener from the inventory. For proper design, I'm trying to determine what the power (or current rating) of the zener diode in the ab...

PeterJ

@jippie, about to head off but not sure for a Cortex / Stellaris off the top of my head but guess it wouldn't make much practical difference, just might be an idea and if 16-bits would fit in RAM that will probably make it faster if an issue.

jippie

@PeterJ yes good point.

JonRB

11:54 AM

@jippie the zener? yes. It speeds up the disengagement. Using just a diode would result in an exponential decay but adding a Zener fixes the decay voltage and thus can be faster (if the zener is like 1v... it probably wouldn't be). The V in V = Ldi/dt is now "fixed" rather than exponential

jippie

@JonRB The diode fixes the voltage at 0.6V, how does a zener change that other than changing the exact voltage?

JonRB

Look at the orientation of the Zener. The Zener fixes the voltage at 0.6+24V

higher voltage, higher rate of decay, faster disengagement time

jippie

yes i did notice that

@JonRB the relay's coil voltage being reversed, is that the idea?

JonRB

yes

jippie

ok, fair enough :-)

@JonRB thnx for your explanation

JonRB

12:01 PM

jippie

/me is out for a little while

JonRB

tbf the diode only "fixes" the voltage if it is > the resistive drop. Because typically this isn't the case, the R-L decay characteristics dominate

2 hours later…

jippie

1:57 PM

Why is the compiler complaining?

int32_t amplitude = amplitudeReal ** 2 + amplitudeImag ** 2;

it works when I type:

int32_t amplitude = amplitudeReal * amplitudeReal  + amplitudeImag * amplitudeImag;

both amplitudeReal and amplitudeImagare int32_t

hmmm .. seems I am confusing C and Perl.

jippie

2:54 PM

Q: What's going on in this 110kV short-circuit video?

This may fall in the weekend-amusement category to a certain extent, but what exactly is going in this 20 sec. video? As far as I can tell they trigger a phase-to-ground and a phase-to-phase short. Is it some kind of legitimate test or someone goofing around? I don't speak Russian, so I can't tel...