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by Joel_Mckay
Wed Dec 12, 2018 12:14 pm
Forum: Advanced users
Topic: Piezo sensor + Database
Replies: 5
Views: 408

Re: Piezo sensor + Database

What makes you think that the OP needs parallel access to the data? Experience building loggers with structures that always eventually degenerated into something that looks like large circular-buffers: ;-) https://en.wikipedia.org/wiki/Producer%E2%80%93consumer_problem https://en.wikipedia.org/wiki...
by Joel_Mckay
Wed Dec 12, 2018 10:41 am
Forum: Advanced users
Topic: Piezo sensor + Database
Replies: 5
Views: 408

Re: Piezo sensor + Database

SQLite is written in C, and is usually not setup to even be thread safe. Thus, it mainly was intended for a standalone program, and is not great for parallel access to the data. Python often relies on SWiG ( http://swig.org/ ) for all of its performance libs. Likewise, Julia wraps just about everyth...
by Joel_Mckay
Wed Dec 12, 2018 8:37 am
Forum: Automation, sensing and robotics
Topic: Looking to do a project and I have no idea what I'm doing
Replies: 2
Views: 128

Re: Looking to do a project and I have no idea what I'm doing

Aprs on a pi3 (usb sound card + UART based gpio ) https://www.marcelpost.com/wiki/index.php/Aprs There are multi-drop gateways people have made: https://github.com/elafargue/aprs-box http://la3t.no/polaricserver Note direwolf is usually 95% of what people need ;-) We tend to play with the older RTL-...
by Joel_Mckay
Wed Dec 12, 2018 7:43 am
Forum: Troubleshooting
Topic: RPi3 Freeze
Replies: 12
Views: 322

Re: RPi3 Freeze

@wg141124 Check the drive free space, and list your device mounts. df -h mount The Read-Only errors can be caused by ignoring a partitions "ro" flag, OS error/crash forced re-mount into safe mode, and or the Flash memory is quietly failing. I suspect with a write-heavy server running that your flash...
by Joel_Mckay
Wed Dec 12, 2018 7:32 am
Forum: Advanced users
Topic: Piezo sensor + Database
Replies: 5
Views: 408

Re: Piezo sensor + Database

MySQL syntax may have changed, but the db user privileges are usually mostly separate from the system user privileges. For example, root user here is mysql's root password, and not a system login password. sudo /usr/bin/mysql_secure_installation mysql -h localhost --user="root" --password="admin_pas...
by Joel_Mckay
Wed Dec 12, 2018 7:13 am
Forum: Advanced users
Topic: Solution: Dedicating one core to a real-time process
Replies: 2
Views: 158

Re: Solution: Dedicating one core to a real-time process

Guaranteed latency OS like LinuxRT essentially install a program as a kernel module.
;-)
Our clubs rc1 variant of Stretch with this kernel will be out Dec. 28, 2018 (includes many updates):
https://sourceforge.net/projects/microm ... pberry-pi/

Cheers,
J
by Joel_Mckay
Sat Dec 08, 2018 11:34 am
Forum: Automation, sensing and robotics
Topic: HELP - Stewart Platform
Replies: 3
Views: 118

Re: HELP - Stewart Platform

a linuxCNC Hexapod uses 6-axis odd kinematics models, and the pi3B+ can barely handle our Cartesian setup. The RT kernel we use is here: https://sourceforge.net/projects/micrometer-cnc-on-raspberry-pi However, I suspect you may find a Pi's limited resources difficult to use for this type of robotics...
by Joel_Mckay
Fri Dec 07, 2018 1:32 am
Forum: Graphics, sound and multimedia
Topic: Compact flash card media players
Replies: 1
Views: 82

Re: Compact flash card media players

Depends what you are doing, and how accurate the timing needs to be. You might be able to do live parallel steams from a VLC rtsp server, and hope the buffers stay relatively well matched. Due to networking and gpu-decoder Latency, the playback mismatch will be difficult to sync up. There are also s...
by Joel_Mckay
Fri Dec 07, 2018 12:38 am
Forum: Troubleshooting
Topic: Data Retrieval from corrupted file system raspberry pi SD card
Replies: 5
Views: 175

Re: Data Retrieval from corrupted file system raspberry pi SD card

Power brown-outs during a write operation can damage some sdcards at the hardware level, and even a surface test may not necessarily show the failed writes. You could use F3 (Fight Flash Fraud) on the pi to flood the drive capacity with pattern files to check for errors ( http://www.micrometer.xyz/c...
by Joel_Mckay
Mon Dec 03, 2018 1:40 am
Forum: Troubleshooting
Topic: Audio problem
Replies: 1
Views: 70

Re: Audio problem

Some updates will force power cycling the SoC to fix it: http://www.micrometer.xyz/cdn/node/74 Also directly check your speakers from the sound utility to make sure nothing is muted ;-) Cheers, J Tip: Also note, on some systems the repo-detached bin dependencies of the files may require you rebuild ...
by Joel_Mckay
Sun Dec 02, 2018 11:02 am
Forum: Advanced users
Topic: Would a backup-script also copy mounted drives?
Replies: 4
Views: 160

Re: Would a backup-script also copy mounted drives?

Although programs like rsync will let you stop at mount points (and stay in one filesystem) yep, see "-x" or "--one-file-system" flag ;-) I simplified a script, so other forum users can adapt it as needed. Cheers, J #!/bin/bash # Joels simple backup script demo # 2018 Dec 2 #bandwidth limit in kiB/...
by Joel_Mckay
Fri Nov 30, 2018 11:08 pm
Forum: Advanced users
Topic: f2fs : why not distribution with root fs as f2fs
Replies: 14
Views: 562

Re: f2fs : why not distribution with root fs as f2fs

I don't understand the sense of "f2fs might be faster..." sentence in relation with the clock of the device I suspect the communication overhead with F2FS may appear more efficient with a linear write in some scenarios (like avoiding partial erasure that can cause a read, modify, and write routine)...
by Joel_Mckay
Thu Nov 29, 2018 7:45 am
Forum: Advanced users
Topic: f2fs : why not distribution with root fs as f2fs
Replies: 14
Views: 562

Re: f2fs : why not distribution with root fs as f2fs

XDA: Interview with Francisco Franco... September 3, 2017. quote a Google engineer which says that based on their test, F2FS doesn’t perform any faster than the ext4 . (Kinda of a poor reference without any details) Have newer SD cards demonstrated better speeds. Maybe it's time to take another loo...
by Joel_Mckay
Wed Nov 28, 2018 8:23 pm
Forum: Graphics, sound and multimedia
Topic: Project to transport Audio over Ethernet
Replies: 5
Views: 288

Re: Project to transport Audio over Ethernet

"Sometimes fun projects just aren't worth the effort these days." So true, as one can get an 8 channel 24 bit pci sound-card for about $150 used off ebay (few people know how to work these), and is documented to be compatible with Ardour: "M-Audio Delta 1010LT PCI Sound-Card" As stated above, for li...
by Joel_Mckay
Wed Nov 28, 2018 10:52 am
Forum: Graphics, sound and multimedia
Topic: Project to transport Audio over Ethernet
Replies: 5
Views: 288

Re: Project to transport Audio over Ethernet

A Pi3 may have enough processor to output a live mic stream over JACK... yet I suspect you will need fairly high-end PCs with additional pci sound-cards to accomplish distributed JACK source mixing. Note, setting up a system with QjackCtl can be overwhelming for new users, but there are ways to auto...
by Joel_Mckay
Wed Nov 28, 2018 6:24 am
Forum: Graphics, sound and multimedia
Topic: Video Editing on Raspberry Pi [2018]
Replies: 1
Views: 193

Re: Video Editing on Raspberry Pi [2018]

Our group uses OpenShot because it can also import image sequences as video. https://sourceforge.net/projects/micrometer-cnc-on-raspberry-pi As for packagers, apt seems to work quite well on the regular Raspbian Stretch, and provides a traceable chain of accountability back to the open build-recipe ...
by Joel_Mckay
Tue Nov 27, 2018 11:03 pm
Forum: Advanced users
Topic: recommended method to switch a High-Power LED off/on?
Replies: 12
Views: 748

Re: recommended method to switch a High-Power LED off/on?

Brandon92 wrote:
Tue Nov 27, 2018 10:23 pm
Because there are a lot of led driver out there. Here are a couple as an example:
Agreed, the MAX20053 looks fairly applicable in a TSSOP, does PWM dimming, and is probably simpler than using something like a LDO LT3083 supply.
;-)
by Joel_Mckay
Tue Nov 27, 2018 6:44 am
Forum: Automation, sensing and robotics
Topic: Getting a stepper working with n928n
Replies: 3
Views: 166

Re: Getting a stepper working with n928n

Without current regulated drivers, they will overheat with excessive loads. The MP6500 2.5A/field modules are pin compatible with A4988 2A/field modules: https://www.pololu.com/category/229/mp6500-stepper-motor-driver-carriers Higher voltages (like 24v on a 5v stepper) usually mean you can step fast...
by Joel_Mckay
Tue Nov 27, 2018 6:32 am
Forum: Automation, sensing and robotics
Topic: 5 in one test strip reader
Replies: 1
Views: 140

Re: 5 in one test strip reader

I would recommend using a calibration card, full spectrum lighting (not a single LED), and a camera with manual focus. OpenCV + v4l2ucp should be able to handle your ROI search, and camera exposure control. Also, by using a contrasting backing tray in the opposite color of your strips: * split cam s...
by Joel_Mckay
Mon Nov 26, 2018 10:20 am
Forum: Automation, sensing and robotics
Topic: AM2302 DHT sensor ignoring sign of temperature....
Replies: 5
Views: 194

Re: AM2302 DHT sensor ignoring sign of temperature....

Personally, I would also look at the DC voltage drop to your sensor-outlets, as you may have to run it from a 12v supply to a local filter capacitor & 3.3v regulator at each destination. If you are using fine-gauge steel-wire, than a supply drop could pose an issue, and you may also have to under-cl...
by Joel_Mckay
Mon Nov 26, 2018 12:18 am
Forum: Automation, sensing and robotics
Topic: AM2302 DHT sensor ignoring sign of temperature....
Replies: 5
Views: 194

Re: AM2302 DHT sensor ignoring sign of temperature....

The DHT11 style 1-wire communication is unreliable in many situations... The driver code usually relies on busy-loop timers, bit-banged protocols, and brute-force polling. To make things even worse, after a few days some devices will simply stop responding to polls, and will magically come back to l...
by Joel_Mckay
Sun Nov 25, 2018 5:29 am
Forum: Automation, sensing and robotics
Topic: How to control 5 Stepper Motors using UART?
Replies: 1
Views: 157

Re: How to control 5 Stepper Motors using UART?

You can buy a cheap RAMPS board for 3D printers that does 5-axis with an Arduino running Marlin or GRBL (for smaller steppers, you can get away with doing this kind of setup). The stepper drivers are the popular A4988 Stepper Motor modules: https://www.pololu.com/product/1182/specs The ULN chips did...
by Joel_Mckay
Sun Nov 25, 2018 1:54 am
Forum: Advanced users
Topic: recommended method to switch a High-Power LED off/on?
Replies: 12
Views: 748

Re: recommended method to switch a High-Power LED off/on?

Well, if you are not to worried about efficiency, than a modified LM317 CC regulator could do for a low-voltage setup. https://www.instructables.com/id/Tiny-Color-Mixer-a-constant-current-3W-RGB-LED-wit/ As I said before, sometimes an LDO linear-regulator can be substituted into a design... if the e...
by Joel_Mckay
Sat Nov 24, 2018 10:15 pm
Forum: Advanced users
Topic: recommended method to switch a High-Power LED off/on?
Replies: 12
Views: 748

Re: recommended method to switch a High-Power LED off/on?

No, the XL4001E1 cannot modulate its output driver section, as the documentation is referring to the regulator's internal PWM.
The key subtle conceptual difference is that it is not a dim-able ballast by itself. :-)

Cheers,
J
by Joel_Mckay
Sat Nov 24, 2018 8:19 pm
Forum: Advanced users
Topic: recommended method to switch a High-Power LED off/on?
Replies: 12
Views: 748

Re: recommended method to switch a High-Power LED off/on?

I searched for something like that, to handle 5V and I found the XL4001E1: That chip is just a DC-to-DC Buck converter that can operate as a Constant-Current power supply. One subtle difference, is that this does not contain a Dimming circuit attached to it's output driver section. It is probably n...

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