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by jbeale
Fri Oct 11, 2019 8:41 pm
Forum: Troubleshooting
Topic: PIR motion sensor outputting every 16th minute
Replies: 6
Views: 120

Re: PIR motion sensor outputting every 16th minute

PIR sensors are detecting an extremely small signal, on the microvolt level. That kind of sensor tends to pick up RFI (radio-frequency interference) so if it is anywhere near a RF transmitter, such as for example a wireless gas or electric meter that might transmit every 15 minutes, that could be a ...
by jbeale
Sat Oct 05, 2019 3:55 am
Forum: General discussion
Topic: Pi4 "networked AI core"?
Replies: 5
Views: 197

Re: Pi4 "networked AI core"?

Cut and pasted from your link: "Your tiny, dual-display, desktop computer …and robot brains, smart home hub, media centre, networked AI core, factory controller, and much more" What that says to me is that *with the right software* it can do these things- as of course could any other SBC, with varyi...
by jbeale
Fri Oct 04, 2019 2:09 am
Forum: Graphics, sound and multimedia
Topic: video analysis from IP camera
Replies: 2
Views: 159

Re: video analysis from IP camera

There are posted examples of facial recognition using the Raspberry Pi, for example https://www.pyimagesearch.com/2018/06/25/raspberry-pi-face-recognition/ don't expect it to work very fast, as this needs a lot of computation. He mentions 1 or 2 FPS for face recognition, but you can get 8 or 10 fps ...
by jbeale
Wed Oct 02, 2019 3:10 am
Forum: Troubleshooting
Topic: RPI4 Ethernet port needs 8 wires?
Replies: 13
Views: 452

Re: RPI4 Ethernet port needs 8 wires?

I am minimizing underground runs of cable, by using a MMF-RJ45 splitter/combiner to run two separate 4-wire 100baseT ethernet circuits through one direct-burial 8-wire Cat5e cable, and one of the two circuits on the far end goes to a Pi in a buried seismic vault. It works. Actually it doesn't go DIR...
by jbeale
Mon Sep 30, 2019 2:27 pm
Forum: General discussion
Topic: How to use RS485 Shield with Raspberry Pi
Replies: 19
Views: 462

Re: How to use RS485 Shield with Raspberry Pi

For the software configuration of the serial interface, it sounds like you are talking about the inittab / sysvinit structure being replaced by systemd, which happened in 2015. Does this thread help?
https://www.raspberrypi.org/forums/view ... p?t=123081
by jbeale
Sat Sep 28, 2019 12:20 am
Forum: Other projects
Topic: 360 degree human presence detection
Replies: 16
Views: 598

Re: 360 degree human presence detection

I've used several kinds of doppler radar sensors. They do work but they will not discriminate between small nearby motion and large distant motion. If you've got a metal frame or metal springs in your mattress, they would likely pick up any motion of those as well. A large mass on a load cell or for...
by jbeale
Thu Sep 26, 2019 4:10 am
Forum: Other projects
Topic: 360 degree human presence detection
Replies: 16
Views: 598

Re: 360 degree human presence detection

You might look up "force sensitive resistor" for example, here's one that is long and thin and costs about $10 per foot. One of the links even mentions "off bed sensor" as a typical application. https://www.adafruit.com/product/1071 https://www.amazon.com/Pressure-SF15-600-Resistance-Type-Resistor-S...
by jbeale
Thu Sep 26, 2019 1:23 am
Forum: Troubleshooting
Topic: [Not getting my full Gigabit internet speed on RPI 4b 4GB]
Replies: 31
Views: 1095

Re: [Not getting my full Gigabit internet speed on RPI 4b 4GB]

A chain is as strong as the weakest link. Your connection between the Pi and the remote speed-test server has a lot of links, both real and virtual. The iperf test ruled out a few possible issues, so that just leaves all the rest... I would consider how that test works, where the data comes from, et...
by jbeale
Wed Sep 25, 2019 2:28 pm
Forum: Beginners
Topic: PIR sensor and night vision
Replies: 2
Views: 125

Re: PIR sensor and night vision

The PIR sensor detects body heat beyond 5 micron (5000 nm), known as "thermal infrared". An IR LED illuminator for the camera emits in the "near infrared" around 850 nm (actually dimly visible, as a dull red glow in the dark). The near-IR LED has a much, much shorter wavelength, and should be comple...
by jbeale
Mon Sep 23, 2019 8:12 pm
Forum: General discussion
Topic: How can i connect and get data from multiple MQ-2 Gas detection Sensors?
Replies: 5
Views: 143

Re: How can i connect and get data from multiple MQ-2 Gas detection Sensors?

If we're talking about this sensor http://wiki.seeedstudio.com/Grove-Gas_Sensor-MQ2/ it is pretty cheap, just the tin-oxide sensor with an adjustable resistor for analog voltage output, and I think no way to control the heater separately. That page claims: "It is suitable for detecting H2, LPG, CH4,...
by jbeale
Mon Sep 23, 2019 2:25 pm
Forum: Automation, sensing and robotics
Topic: Raspberry Pi model 3B video processing speed
Replies: 5
Views: 249

Re: Raspberry Pi model 3B video processing speed

simple motion detection is done on a Pi by the PiKrellCam https://billw2.github.io/pikrellcam/pikrellcam.html package basically as a side-effect of the H.264 compression, which has to calculate motion vectors anyway, so it has the same GPU, CPU and power footprint as simply recording video and it wo...
by jbeale
Sun Sep 22, 2019 2:47 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: PWM input clock (clk_pwm) frequency for Pi4
Replies: 9
Views: 380

Re: PWM input clock (clk_pwm) frequency for Pi4

An oscilloscope could show what the difference is. If you don't have one, but if you can post the code, then someone who does have one might be able to check what the signals look like. I've got a scope and a Pi3B but I don't have a Pi4. Is your code generating the pulses using PWM hardware, or is i...
by jbeale
Sat Sep 21, 2019 7:09 pm
Forum: Media centres
Topic: Hard disk always connected - dangerous?
Replies: 7
Views: 392

Re: Hard disk always connected - dangerous?

The best real-world data we have on consumer-grade HDD reliability, as far as I know, is this based on Google's server farms. Google uses (and uses up) more hard drives than any other company on the planet, as far as I know. https://storagemojo.com/2007/02/19/googles-disk-failure-experience/ I presu...
by jbeale
Sat Sep 21, 2019 3:17 pm
Forum: Other projects
Topic: 360 degree human presence detection
Replies: 16
Views: 598

Re: 360 degree human presence detection

I can see why in a hospital, nursing home, or home care setting there would be reasons this information is interesting. On the sensor side the choices are different if you demand this must work even if the sensor may be covered by sheets or blankets that would absorb ultrasonic pulses. Doppler radar...
by jbeale
Sat Sep 21, 2019 3:01 pm
Forum: Camera board
Topic: Camera line_time_ns demonstration
Replies: 2
Views: 148

Re: Camera line_time_ns demonstration

Very interesting experiment, thanks for posting this.
Note if the light flash rate was 3 kHz I think the interval is 1/3 millisecond, not 1/3 microsecond (?)
by jbeale
Tue Sep 17, 2019 12:42 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Maximum length of ethernet cable between Raspberry Pi and camera
Replies: 8
Views: 344

Re: Maximum length of ethernet cable between Raspberry Pi and camera

In my use case with a thin HDMI cable, there was no interference, but then it was outdoors with no other signal sources anywhere around. If you have other cables or signal sources immediately adjacent, then I would expect some effects. Other things being equal, I would expect an HDMI cable to be les...
by jbeale
Mon Sep 16, 2019 7:23 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Maximum length of ethernet cable between Raspberry Pi and camera
Replies: 8
Views: 344

Re: Maximum length of ethernet cable between Raspberry Pi and camera

I'm aware of an adaptor for RPi camera extension using HDMI cable, which I have used. I used a very thin and flexible type of HDMI cable (only a few mm in diameter, and less than 1m long) and it worked. This version claims a 5 meter HDMI cable works: https://www.tindie.com/products/freto/pi-camera-h...
by jbeale
Fri Sep 13, 2019 2:16 pm
Forum: General discussion
Topic: 12v battery + 25 watt Solar = always powered 4B?
Replies: 17
Views: 692

Re: 12v battery + 25 watt Solar = always powered 4B?

I have used a "moteino" which is Arduino with RFM69HW radio module. Range is plenty good enough for me: "~540 meters range @38400kbps with lots of trees and one or two buildings inbetween." https://lowpowerlab.com/forum/rf-range-antennas-rfm69-library/rfm69hw-range-test!/ The same unit is also avail...
by jbeale
Fri Aug 30, 2019 2:50 pm
Forum: Graphics, sound and multimedia
Topic: sound of thunder / speaker test
Replies: 1
Views: 174

Re: sound of thunder / speaker test

BTW it turns out electret mics do not like high humidity and condensation, which we have plenty of in Oregon. The trick for outdoor recording use was to mount the mic on the small end of an exponential horn. The horn throat was filled with a wispy material (stretched-out pillow stuffing) to reduce a...
by jbeale
Fri Aug 30, 2019 2:19 pm
Forum: Graphics, sound and multimedia
Topic: sound of thunder / speaker test
Replies: 1
Views: 174

sound of thunder / speaker test

Just FYI... one of my R-Pi boards is under the roof eaves along the back of the house, recording ambient nature sounds. I am using a small-electret stereo microphone and preamp that I built, going into a Behringer Line2USB cable to the Pi. Last night there was some thunder along with the rain, which...
by jbeale
Fri Aug 23, 2019 3:31 pm
Forum: Off topic discussion
Topic: Best Raspberry Pi Alternatives 2019
Replies: 62
Views: 4853

Re: Best Raspberry Pi Alternatives 2019

> how successful it's been in introducing youngsters to computing?

My take: there is no one thing that magically makes many people interested in computing who didn't already have some interest. For those who are interested (of any age) the R-Pi is a great choice, and an unusually good value.
by jbeale
Fri Aug 23, 2019 5:00 am
Forum: Troubleshooting
Topic: ads1115 strange output
Replies: 2
Views: 150

Re: ads1115 strange output

I don't know any details of your setup, but what kind of electronics does your pH probe contain? In other words what does that BNC connect to, does it contain batteries or use external power? According to one vendor's datasheet https://www.analog.com/en/design-center/reference-designs/circuit-collec...
by jbeale
Sat Aug 17, 2019 7:05 pm
Forum: Camera board
Topic: PiKrellCam: motion vector detect + OSD web interface
Replies: 1462
Views: 325104

Re: PiKrellCam: motion vector detect + OSD web interface

I had not paid much attention to how all this works, but I think at least on my system that the entire day's videos are simply moved to the archive folder around midnight. I was doing those experiments right around midnight, so the process of archiving may have just happened. At least on my system, ...
by jbeale
Sat Aug 17, 2019 7:07 am
Forum: Camera board
Topic: PiKrellCam: motion vector detect + OSD web interface
Replies: 1462
Views: 325104

Re: PiKrellCam: motion vector detect + OSD web interface

I have a few Pi's running PiKrellcam v4.2.1. In addition to motion capture, it takes a still photo every other hour. The still images are triggered by this line in my crontab: # take one still photo every other hour 7am-5pm 0 7-17/2 * * * echo "still" > /home/pi/pikrellcam/www/FIFO PiKrellCam also d...
by jbeale
Thu Aug 15, 2019 3:31 pm
Forum: Troubleshooting
Topic: Four dead Pis in one class!?
Replies: 15
Views: 918

Re: Four dead Pis in one class!?

It is true that using the Micro-USB power input is safer than trying to connect +5V directly to the GPIO pins, where there's one way to do it right and lots of ways to immediately smoke the Pi. However that is a completely separate issue from whether you are using two physically separate battery pac...

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