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by amcdonley
Sun Sep 08, 2019 4:44 pm
Forum: Automation, sensing and robotics
Topic: Challenge of Powering Robot 24/7
Replies: 6
Views: 807

Re: Challenge of Powering Robot 24/7

You should get a higher number of cycles with LiFePO4 cells. ... Some guys don't get enough for 24/7 from 30W ... It's a challenge.all right. The 8x NiMH AA cells fit in 4x4x1.25 inches and deliver 18-21 Watt-Hours (318mA idle * 9.6v nominal * 6 to 7 hours "fairly idle play time"). What a...
by amcdonley
Sun Sep 08, 2019 4:26 pm
Forum: Automation, sensing and robotics
Topic: Challenge of Powering Robot 24/7
Replies: 6
Views: 807

Re: Challenge of Powering Robot 24/7

A dc-dc buck converter ... charging equalizers ... PS It would be just as interesting to explain how the charger works mechanically and how the robot locates it and plugs in. Yes, powering my bot would need some combination of converters, equalizers AND UPS function. The total requirements / constr...
by amcdonley
Sat Sep 07, 2019 3:48 pm
Forum: Automation, sensing and robotics
Topic: Challenge of Powering Robot 24/7
Replies: 6
Views: 807

Challenge of Powering Robot 24/7

For more than 20 years I have wanted my robots to become independent - managing their own charging to allow 24/7 operation. This year, with a GoPiGo3 robot, I substantially achieved this goal, and have learned more about the challenges facing a 24/7 robot. Specifically, in my case, the capacity of N...
by amcdonley
Mon Aug 26, 2019 7:16 pm
Forum: Automation, sensing and robotics
Topic: HDMI Off Power Saving Reality
Replies: 1
Views: 782

HDMI Off Power Saving Reality

After reading I could save 25mA by turning off the HDMI interface on my RPi 3B robot, with the command "sudo /usr/bin/tvservice -o", I was expecting to see my robot enjoying an extra 20 minutes of idle playtime. It would appear to be less than 6 minutes, or perhaps nothing at all when no d...
by amcdonley
Sat Aug 24, 2019 4:28 pm
Forum: Automation, sensing and robotics
Topic: Data Logging, Plotting Help
Replies: 10
Views: 3803

Local: Data Logging, Plotting

For simple logging sensor data to a file and then plotting it, all local: 1) Log Battery Voltage and Plot on linear scale by hour of day, and by time since first measurement 2) Log PiCamera Brightness Value and Plot on log scale by hour of day It is also possible to tie sensor readings into the RPi-...
by amcdonley
Mon Aug 19, 2019 7:16 pm
Forum: Automation, sensing and robotics
Topic: Simple Variable Sharing Between Python Processes?
Replies: 4
Views: 1910

Re: Simple Variable Sharing Between Python Processes?

You may consider a generic messaging queue (eg mosquitto) to communicate state changes across processes. I have to admit I am intimidated by the whole IoT complexity. I've watched rosie the red robot as he ventured there, but I have kept my distance. After 40+ years of doing commercial software sys...
by amcdonley
Mon Aug 19, 2019 6:28 pm
Forum: Automation, sensing and robotics
Topic: Simple Variable Sharing Between Python Processes?
Replies: 4
Views: 1910

Re: Simple Variable Sharing Between Python Processes?

SQLite3 doesn't support multiple writers. You very rapidly destroy your database if you get two writers running. Use python multi-threading to run everything in a single python process. Results on my Pi3B using multiprocessing pool.map to 3 "worker/inserter" processes that each obtain clo...
by amcdonley
Mon Aug 19, 2019 1:03 am
Forum: Automation, sensing and robotics
Topic: Simple Variable Sharing Between Python Processes?
Replies: 4
Views: 1910

Simple Variable Sharing Between Python Processes?

Right now I have a python module to manage concurrent access to some robot variables stored in a file "carlData.json" carlDataJason.py : * saveCarlData(dataname, datavalue, logit=False) # adds datanaem:datavalue to carlData.json file * getCarlData(dataname=None) # either returns dictionary...
by amcdonley
Sat Aug 17, 2019 7:05 pm
Forum: Automation, sensing and robotics
Topic: Raspberry Pi High Frequency Sampling
Replies: 5
Views: 2023

Re: Raspberry Pi High Frequency Sampling

That is samples per second, not bytes per second. So if each sample was 12 bytes (4 bytes each of X, Y, Z) then that would be 20,000 times 12 or 240,000 bytes per second. The top line is 1 byte per second, the bottom line slower for 5 bytes per second, which implies 12 bytes per second will be even...
by amcdonley
Sat Aug 17, 2019 4:34 pm
Forum: Automation, sensing and robotics
Topic: Raspberry Pi High Frequency Sampling
Replies: 5
Views: 2023

Re: Raspberry Pi High Frequency Sampling

Hey guys, ADXL355 digital accelerometer over SPI and would like to sample at 4000hz. Does the pi have a maximum sampling rate cap, According to How Fast Is SPI the Linux SPI driver (in a C language program) seems to max out around 20K bytes per second. I don't know how many bytes each ADXL355 sampl...
by amcdonley
Fri Aug 09, 2019 10:43 pm
Forum: Troubleshooting
Topic: RPi 3B WiFi Down - recovered by unplug, replug dongle
Replies: 1
Views: 227

Re: RPi 3B WiFi Down - recovered by unplug, replug dongle

I think I see what happened - a few hours prior I did a: sudo rpi-clone sda and after it finished and unmounted both partitions, I unplugged the USB microSDcard adapter. Guess that did it. /var/log/messages: Aug 9 17:54:35 Carl kernel: [171141.137968] usb 1-1.4: USB disconnect, device number 5 Aug 9...
by amcdonley
Fri Aug 09, 2019 10:21 pm
Forum: Troubleshooting
Topic: RPi 3B WiFi Down - recovered by unplug, replug dongle
Replies: 1
Views: 227

RPi 3B WiFi Down - recovered by unplug, replug dongle

I just found my RPi 3B robot incommunicado by both wlan0 and wlan1 and this printed on the closed remote SSH login: packet_write_wait: Connection to 10.0.0.188 port 22: Broken pipe In spite of a solid blue light on the WiFi dongle, the RPI disk activity light seemed to indicate the bot was still run...
by amcdonley
Tue Aug 06, 2019 6:54 pm
Forum: Astro Pi
Topic: PiCamera as Luminosity Sensor?
Replies: 8
Views: 8068

PiCamera as Luminosity Sensor - Python Code Available?

Would love a post project report and to see luminosity sensor code.

I want to use PiCamera (v1.3) to measure room light level over 24hr periods - don't need calibrated value, just continuous values from darkness to brightly lit.
by amcdonley
Fri Aug 02, 2019 9:20 pm
Forum: Automation, sensing and robotics
Topic: Agree? “IMU worthless for simple robots' x, y, heading?”
Replies: 9
Views: 1141

Re: Agree? “IMU worthless for simple robots' x, y, heading?”

You might be right but the question on the title I answered to was different than the one you are thinking at, since it did not had the "x, y heading" words at the end.. Kind of author changes its ckick-baity question then argues people gave him wrong answers, Please - I asked my question...
by amcdonley
Thu Aug 01, 2019 1:08 am
Forum: Automation, sensing and robotics
Topic: Robot Shared Values / DB impact on RPi SD card
Replies: 2
Views: 423

Re: Robot Shared Values / DB impact on RPi SD card

Thank you - great response. consider in memory databases https://en.wikipedia.org/wiki/List_of_in-memory_databases Or. if it suits you, a faster in memory key-value datastore like LMDB https://en.wikipedia.org/wiki/Lightning_Memory-Mapped_Database I have heard of, but know nothing about, SQLite whic...
by amcdonley
Wed Jul 31, 2019 8:32 pm
Forum: Automation, sensing and robotics
Topic: Agree? “IMU worthless for simple robots' x, y, heading?”
Replies: 9
Views: 1141

Re: Agree? “IMU worthless for simple robots”

blimpyway wrote:
Wed Jul 31, 2019 8:09 pm
try to make a simple two wheel balancing bot (segway bot) without an imu.
Understandably impossible for the "keeping its head up" function, but can it provide accurate (world frame: x, y, theta)? It's a serious question. Am I wrong about that application of IMU?
by amcdonley
Wed Jul 31, 2019 5:29 pm
Forum: Automation, sensing and robotics
Topic: Agree? “IMU worthless for simple robots' x, y, heading?”
Replies: 9
Views: 1141

Agree? “IMU worthless for simple robots' x, y, heading?”

Found a phenomenal [90 page introduction and analysis](https://arxiv.org/pdf/1704.06053.pdf) (university level, but first and last sentence of some paragraphs are understandable): Manon Kok, Jeroen D. Hol and Thomas B. Sch ̈on (2017), ”Using Inertial Sensors for Position and Orientation Estimation”,...
by amcdonley
Wed Jul 31, 2019 5:16 pm
Forum: Automation, sensing and robotics
Topic: Robot Shared Values / DB impact on RPi SD card
Replies: 2
Views: 423

Robot Shared Values / DB impact on RPi SD card

My robot is nearing the point of needing a place to share more state and history between Python processes. Currently I have a “json data module” that abstracts access to a few rarely written values persisted on the SD card file system, and two logger files which are written to once or twice an hour....
by amcdonley
Sun Jul 28, 2019 4:07 am
Forum: Automation, sensing and robotics
Topic: 'Uninteruptible' Power Supply
Replies: 3
Views: 525

Re: 'Uninteruptible' Power Supply

strongly suggest this UPS, I use it with my desktop RPi for over a year with no off time, even through hurricanes.

https://lifepo4wered.com/lifepo4wered-pi+.html
by amcdonley
Thu Jun 20, 2019 5:46 pm
Forum: Automation, sensing and robotics
Topic: Let's give voice to my robot... Speaker problem
Replies: 11
Views: 1786

Re: Let's give voice to my robot... Speaker problem

drotosclerosi wrote:
Wed Jun 19, 2019 2:29 pm
So i bought this little speaker

I'm just worried about the weight: could a 42grams speaker connected to the 3.5 mm jack damage it in any way?
Use a short extension cable and velcro the speaker to your bot.
by amcdonley
Tue Jun 18, 2019 12:52 pm
Forum: Automation, sensing and robotics
Topic: irritating battery limits
Replies: 21
Views: 2187

Re: irritating battery limits

OK, so i took a look at that specialized battery, and it definitely looks intriguing. The problem lies in that this solution would only work for the pi part of the robot, and would not allow function for the rest whilst charging. Ideally, I would need a circuit that could take a signal from a GPIO ...
by amcdonley
Sun Jun 16, 2019 10:19 pm
Forum: Automation, sensing and robotics
Topic: irritating battery limits
Replies: 21
Views: 2187

Re: irritating battery limits

Have you looked at this phenomenal UPS https://lifepo4wered.com/lifepo4wered-pi+.html ?

I have the earlier version running a desktop RPi continuously for six months at a time. I like to update the OS periodically and sometimes that requires a reboot.
by amcdonley
Sun Jun 16, 2019 1:02 pm
Forum: Automation, sensing and robotics
Topic: How to maximize Robot Play Time - NiMH Batteries?
Replies: 6
Views: 964

Re: How to maximize Robot Play Time - NiMH Batteries?

Are you using the batteries with UPS to run both the RPi and the motors?? My bot is built upon the Dexter Industries GoPiGo3, which provides the power management and isolation using a single 7 to 12 v 2.5A source. Note: I have found it best for me to start from a supported platform. I spent/wasted ...
by amcdonley
Sat Jun 15, 2019 12:42 pm
Forum: Automation, sensing and robotics
Topic: Let's give voice to my robot... Speaker problem
Replies: 11
Views: 1786

Re: Installing OpenCV

THe fact is that i'm already in big pain installing opencv for facial recognition If you are willing to use Python and not virtual environments: (From https://www.pyimagesearch.com/2018/09/19/pip-install-opencv/) sudo apt-get update && sudo apt-get upgrade sudo apt-get install libhdf5-dev l...
by amcdonley
Sat Jun 15, 2019 12:17 pm
Forum: Automation, sensing and robotics
Topic: How to maximize Robot Play Time - NiMH Batteries?
Replies: 6
Views: 964

Re: How to maximize Robot Play Time - NiMH Batteries?

I usually use Hobby Lipo batteries for all my projects as they are cheaper and have higher energy density as well as can handle much higher amps if needed. But I would guess you are not running them in a UPS (uninterruptable power supply) mode that allows connecting/disconnecting the charging sourc...

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