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by experix
Thu May 14, 2015 2:42 pm
Forum: Off topic discussion
Topic: Benchmark my code [completed]
Replies: 7
Views: 933

Re: Benchmark my code

I can give you execution times and performance notes (I assume that's what you mean by benchmark) on my B+, and I'll probably get a model 2 soon. In addition, if it doesn't look like too much work, I'll translate it into experix for comparison (drawing graphs is likely to be much faster). Can you em...
by experix
Tue May 12, 2015 3:08 pm
Forum: C/C++
Topic: Serial port in C - how to get it close to "real time"?
Replies: 16
Views: 6844

Re: Serial port in C - how to get it close to "real time"?

If you are using the serial port in the usual way, via open,read,write on /dev/ttyAMA0, that's a serious bottleneck because you are doing a user-kernel and kernel-user transition on each little transaction. I got much higher data rates (about 7 x on some gertbot experiments) by writing my own serial...
by experix
Sat May 09, 2015 5:00 pm
Forum: Off topic discussion
Topic: In search of a quiet mini-computer
Replies: 94
Views: 11995

Re: In search of a quiet mini-computer

There are a lot of useful suggestions in this thread, mainly about careful trials. This is not easy to do right. But before embarking on a big complicated double-blind trial and doing all the appropriate statistical analysis to ensure validity, let's check some basics. Did you use the model 2 with t...
by experix
Tue May 05, 2015 3:24 pm
Forum: C/C++
Topic: Scan USB for device ID
Replies: 1
Views: 812

Re: Scan USB for device ID

libusb has functions for this and related things. There's some confusion about the libusbx fork and obsolete webpages, but it looks like the right one now is http://libusb.info . Your Linux system probably has libusb on it, but you might need to download header files in order to do programming. It's...
by experix
Tue May 05, 2015 3:11 pm
Forum: General discussion
Topic: PI project for University
Replies: 1
Views: 347

Re: PI project for University

If you ask around in the science departments you might find a prof or grad student who wants to set up something that involves data collection, analysis, imagery, control and so forth. The RPi can do all of these things, but chances are the people you talk to won't have a clue. The only thing they c...
by experix
Thu Apr 30, 2015 9:29 pm
Forum: General discussion
Topic: data transfer: compress it? how?
Replies: 3
Views: 930

Re: data transfer: compress it? how?

lzlib isn't GNU. zlib is the nearest as it supports reading and writing gzip files. lzlib is LZMA based whereas gzip is DEFLATE, similar but not the same. LZMA generally compresses better but takes longer to do so. oops! I found lzlib thru the GNU software directory but overlooked the statement tha...
by experix
Thu Apr 30, 2015 6:02 pm
Forum: General discussion
Topic: data transfer: compress it? how?
Replies: 3
Views: 930

data transfer: compress it? how?

Robotic and remote sensing projects need to store and transfer data for many purposes: -- command and control -- images -- sensor scans -- whatever Compression may help by affording better utilization of the storage capacity and communication channel bandwidth. But it imposes costs in terms of progr...
by experix
Thu Apr 16, 2015 7:12 pm
Forum: Advanced users
Topic: experix release r15: headless
Replies: 0
Views: 261

experix release r15: headless

If you like to put your Raspberry Pi in a tree or a robot, you are going to love experix_r15! You can run experix headless, communicating over a net connection with the experix_head program. Graphs and pictures appear on your workstation while you send commands to your robot as it explores Olympus M...
by experix
Wed Apr 15, 2015 2:59 pm
Forum: C/C++
Topic: IDE for C++
Replies: 12
Views: 27867

Re: IDE for C++

I haven't used an IDE in years. I'm working in C (maybe there are good reasons to use an IDE with C++? I don't know) and my programs run in text terminals (they don't use X or gui). To me the IDE adds a layer of complication with little benefit. I like to use one text terminal with my modified nano ...
by experix
Mon Apr 13, 2015 3:05 pm
Forum: C/C++
Topic: math problems in C
Replies: 12
Views: 3526

Re: math problems in C

Thank you, BMardle and jojopi, for setting me straight. My only excuse is that I do pay attention to those compiler warnings about wrong-type arguments and fix them in my code before I get to the testing phase, so I have not run into that kind of trouble with printf. But I have done considerable wor...
by experix
Sat Apr 11, 2015 4:44 pm
Forum: C/C++
Topic: math problems in C
Replies: 12
Views: 3526

Re: math problems in C

I admit I'm stumped. I'm thinking I have to go back and check every bit of arithmetic in all of my programs. Try this and compare the results I have put in a comment beneath the code. Why is it correct only in that infinitely pedantic last try? /* gcc -g -Wall -o temp temp.c */ #include <stdio.h> #d...
by experix
Sat Apr 11, 2015 3:46 pm
Forum: For sale
Topic: Is it possible offer help for money?
Replies: 12
Views: 1926

Re: Is it possible offer help for money?

Maybe there should be a forum category for this. Two things to suggest: post something about yourself, your interests and experience and what kinds of things you want to work on. Look at problems that other people are asking for advice on and see if you have something to contribute.
by experix
Wed Apr 08, 2015 2:42 pm
Forum: General discussion
Topic: Sampling High Frequency
Replies: 22
Views: 15851

Re: Sampling High Frequency

Your remarks about filtering and fft make me think your problem might really need a lower sample rate, but the noise causes problems. In that case you could put a filter before the ADC.
by experix
Wed Apr 01, 2015 3:06 pm
Forum: General discussion
Topic: Just announced: the Raspberry Model C
Replies: 23
Views: 3683

Model C still using CONFIG_DISK_SPIN_RANDOMIZE?

Rasbian has been compiled in the past with CONFIG_DISK_SPIN_RANDOMIZE. It makes a random choice for disk spin direction on each boot. This was introduced in 1976 when it was noticed that billions of disk drives all spinning in the same direction were changing the earth's rotation rate, causing clima...
by experix
Tue Mar 24, 2015 2:20 pm
Forum: General discussion
Topic: Beginner needs help with a computer project.
Replies: 22
Views: 3342

Re: Beginner needs help with a computer project.

A super powerful computer is really cool, but it's only a pile of junk until you have something for it to do. Give us an idea of the kinds of projects you want to undertake.
by experix
Tue Mar 24, 2015 2:15 pm
Forum: General discussion
Topic: Pi Project Ideas
Replies: 14
Views: 2150

Re: Pi Project Ideas

How about an experix robot of some sort? Use experix to bind together all the little pieces-- motor control, ADC input, whatever else. Your scripts will include all aspects of the operation: device control via GPIO and USB, data conversion and scaling, graph drawing, picture display, file i/o. I'll ...
by experix
Sat Mar 14, 2015 6:32 pm
Forum: Automation, sensing and robotics
Topic: Digital Pots And GPIO
Replies: 13
Views: 2838

Re: Digital Pots And GPIO

The Pi's GPIO header only exposes one PWM, so to do three of them you need something like the gertbot. It has four PWMs which you control via serial-port writes to the gertbot's processor. Actually, PWM is used to control LED brightness in all sorts of things, such as flashlights, bicycle taillights...
by experix
Sat Mar 14, 2015 5:02 pm
Forum: General programming discussion
Topic: Which language?
Replies: 30
Views: 3900

Re: Which language?

Will you consider adding experix to the list? You can write scripts that run specialized USB things and stuff on the GPIO, do all sorts of calculations on the data they give back, and draw pretty graphs of the results. By running the device-operating script in a thread, you can control it and do oth...
by experix
Fri Mar 13, 2015 1:47 pm
Forum: C/C++
Topic: Fastest GPIO access method
Replies: 5
Views: 2342

Re: Fastest GPIO access method

Hi, You mean are there two ways of wiringPi library usage one with sysfs & other with mmap? In wiringPi.c look at the functions wiringPiSetupPhys and wiringPiSetupSys at the end of that file. They set the variable wiringPiMode to the values WPI_MODE_PHYS and WPI_MODE_GPIO_SYS, respectively. That de...
by experix
Thu Mar 12, 2015 2:30 pm
Forum: C/C++
Topic: PutPixel?
Replies: 9
Views: 2030

Re: PutPixel?

See http://experix.sourceforge.net for framebuffer graphics functions which you can use in a console (i.e. not in X). The graphics primitives are in dist/source/svgalib/frbflib.c; higher-level stuff like graph-drawing and variable-pitch bitmap fonts are in svgafunc.c and experix uses this via a simp...
by experix
Thu Mar 12, 2015 2:19 pm
Forum: C/C++
Topic: Fastest GPIO access method
Replies: 5
Views: 2342

Re: Fastest GPIO access method

wiringPi gives you a choice of accessing GPIO via sysfs (which would be slow) or doing memory-mapped i/o directly. Maybe the comparison you mention was using the sysfs method.
by experix
Wed Mar 11, 2015 2:54 pm
Forum: Off topic discussion
Topic: Pi Store
Replies: 4
Views: 742

Re: Pi Store

It seems to be accessible only via an app on the RPi. I do my forum browsing with my Trisquel thinkpad, and don't want to go to the trouble of booting up the RPi and connecting the internet (which I can't do if the RPi is at home because I have no internet there), merely to find out what the store o...
by experix
Fri Feb 27, 2015 3:35 pm
Forum: General discussion
Topic: An idea for Headless Operation.
Replies: 4
Views: 729

Re: An idea for Headless Operation.

maybe this is a bit off-topic, but-- I have a program with its idiosyncratic display language that I want to run headless. The program needs to get a command line via readline() and turn the echos from readline (going over stdout) into display commands that go over the network to the remote 'head'. ...
by experix
Wed Feb 25, 2015 3:35 pm
Forum: General discussion
Topic: Pi controlled Laser system.
Replies: 2
Views: 549

Re: Pi controlled Laser system.

For control and data acquisition and display on a project like that, look at http://experix.sourceforge.net. My unfinished laser modulation and photon counting project is at http://sourceforge.net/projects/experix ... pld-stuff/.
by experix
Tue Feb 17, 2015 3:37 pm
Forum: Beginners
Topic: Changing volume using potentiometer
Replies: 5
Views: 6286

Re: Changing volume using potentiometer

I'm surprised nobody else picked up on this: your 3rd circuit seems to show an RPi GPIO pin used as an analog input. The RPi does not have any analog circuitry, such as the ADC that you need to make this idea work. So you need to get a ADC chip or one of the many GPIO add-on boards that have them.

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