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by pfletch101
Thu May 23, 2019 3:42 pm
Forum: General discussion
Topic: Static IP Address
Replies: 2
Views: 80

Re: Static IP Address

In my opinion (and that of a number of others who have weighed in on this question in the past), the preferred way of doing this is by setting up your router to assign this IP address to your Pi, based on its MAC address. You can determine the latter by typing (for a wired connection): ifconfig eth0...
by pfletch101
Mon May 20, 2019 7:25 pm
Forum: Automation, sensing and robotics
Topic: DS18B20: Influence of supply voltage on temperature
Replies: 15
Views: 392

Re: DS18B20: Influence of supply voltage on temperature

that the almost certainly increased 'wasted' current flow with increased supply voltage through the circuitry around the sensor was heating it up, so that it was correctly reading a higher temperature. I still don't think so. These sensors have been around for decades, long before Raspberry Pis exi...
by pfletch101
Sat May 18, 2019 7:12 pm
Forum: Automation, sensing and robotics
Topic: DS18B20: Influence of supply voltage on temperature
Replies: 15
Views: 392

Re: DS18B20: Influence of supply voltage on temperature

But to answer your question, I am not sure why the change in Vdd to the sensor would change the temperature reading. Could it be something as simple as heating due to increased power dissipation in the sensor at the higher supply voltage? Scrubbing the data sheet for the sensor, there is nothing to...
by pfletch101
Thu May 16, 2019 7:25 pm
Forum: General discussion
Topic: my service is not starting at power up [solved]
Replies: 16
Views: 292

Re: my service is not starting at power up

You should modify your script so it does not die if the service it depends on is not available. How can I do that? In one important sense, you can't! If the service it depends on doesn't start up at all and/or fails after starting up normally, your script presumably cannot start or carry on. What y...
by pfletch101
Thu May 16, 2019 2:04 pm
Forum: General discussion
Topic: my service is not starting at power up [solved]
Replies: 16
Views: 292

Re: my service is not starting at power up

I'm running a Blynk script using Python in this matter: phone app <-> server <-> script. Threfore, if the local server (installed on the same board where my code is running) is not up and running before the script's execution, the service call fails. That's to be expected as it makes sense. I just ...
by pfletch101
Wed May 15, 2019 10:14 pm
Forum: General discussion
Topic: my service is not starting at power up [solved]
Replies: 16
Views: 292

Re: my service is not starting at power up [SOLVED]

No, no graphics involved. Python code is trying to connectet to a local (127.0.0.1) server. it appears that the below line helped delaying the script thus solving my issue. ExecStartPre=/bin/sleep 30 Thank you. That (or an equivalent) was going to be my next suggestion. It doesn't really fix the un...
by pfletch101
Wed May 15, 2019 10:00 pm
Forum: General discussion
Topic: my service is not starting at power up [solved]
Replies: 16
Views: 292

Re: my service is not starting at power up

As Paeryn implies, the script must be assuming something about its environment that is true in a running system but not true when the system is in the process of booting up. The usual culprit is networking, but this does not seem to be the case here. If the script does do something with graphics, it...
by pfletch101
Wed May 15, 2019 8:00 pm
Forum: General discussion
Topic: my service is not starting at power up [solved]
Replies: 16
Views: 292

Re: my service is not starting at power up

It would probably help if you posted your system unit file (in code tags) here. However, I have one further thought: have you set up the unit file to start it after networking is fully loaded and available?

Code: Select all

After=network-online.target
in the [Unit] section.
by pfletch101
Wed May 15, 2019 7:16 pm
Forum: Automation, sensing and robotics
Topic: DS18B20: Influence of supply voltage on temperature
Replies: 15
Views: 392

Re: DS18B20: Influence of supply voltage on temperature

ptimlin wrote:
Wed May 15, 2019 5:37 pm
But to answer your question, I am not sure why the change in Vdd to the sensor would change the temperature reading.
Could it be something as simple as heating due to increased power dissipation in the sensor at the higher supply voltage?
by pfletch101
Wed May 15, 2019 6:53 pm
Forum: Beginners
Topic: Network Problem?
Replies: 7
Views: 152

Re: Network Problem?

It would appear that you don't have a hard-wired network connection and that your WiFi connection is not set up correctly (most likely you haven't specified your WiFi country , so it doesn't know what frequencies to scan in looking for available networks). Click on the raspberry on the top left of y...
by pfletch101
Wed May 15, 2019 6:34 pm
Forum: General discussion
Topic: my service is not starting at power up [solved]
Replies: 16
Views: 292

Re: my service is not starting at power up

Have you enabled it? This is required to have it start automatically when the system boots.

Code: Select all

sudo systemctl enable blynkscript.service
by pfletch101
Tue May 07, 2019 11:54 pm
Forum: Python
Topic: I wrote a program in Python but I want to send data to a JavaScript program
Replies: 6
Views: 206

Re: I wrote a program in Python but I want to send data to a JavaScript program

One answer is to use a directory that has been mapped to tmpfs (data kept in RAM rather than on disk). I have found that the published recipes for modifying fstab to add additional tmpfs mounts freeze my system when the revised fstab is loaded, but a number of directories (including /run) are mapped...
by pfletch101
Tue May 07, 2019 10:22 pm
Forum: General discussion
Topic: RPi for button presser
Replies: 19
Views: 447

Re: RPi for button presser

It looks as if your only source of power is the 5V supply from the Pi's GPIO. That is still (at the very least) not ideal for a solenoid. If the rest of your wiring is correct (difficult to tell from the picture), I am a bit surprised that the Pi is not rebooting as a result of the power drain when ...
by pfletch101
Sat May 04, 2019 10:39 pm
Forum: Beginners
Topic: Why does the requests.post keep firing?
Replies: 6
Views: 168

Re: Why does the requests.post keep firing?

duckredbeard wrote:
Sat May 04, 2019 9:20 pm
It doesn't like the "if logic = 0" line. Invalid syntax. Tried changing the value to 1 and ran again. No help.
should be

Code: Select all

if logic == [test_value]:
You're testing for equality - not assigning!!
by pfletch101
Thu May 02, 2019 7:26 pm
Forum: Other projects
Topic: Automate water heater - Temp sensor/110v relay/switch
Replies: 4
Views: 229

Re: Automate water heater - Temp sensor/110v relay/switch

Hi guys, I'm quite familiar with computer/linux etc but didn't even know about Raspberry PI until someone tells me I could probably do what I want with it. Here's what I'd like to do, can you please advise on what you'd use? I basically need to read the temp of a water tank, and create a condition ...
by pfletch101
Thu May 02, 2019 7:08 pm
Forum: Troubleshooting
Topic: wifi simultaneous access number
Replies: 1
Views: 53

Re: wifi simultaneous access number

Practical connection limits depend on what the connected devices are doing. 14 sounds reasonably good for light use, but would be extremely optimistic for (e.g.) simultaneous video streaming, even if the source is local. I think that 40 would be optimistic, even for very light use of the individual ...
by pfletch101
Thu May 02, 2019 3:46 pm
Forum: Beginners
Topic: Reading several inputs for same counter
Replies: 6
Views: 208

Re: Reading several inputs for same counter

In general, if you are dealing with multiple asynchronous events (your button presses in this case) and want to record each one without interference from any of the others, you would need to have a separate subprocess (not just a separate thread) for each event, to work around Python's limitation to...
by pfletch101
Wed May 01, 2019 8:44 pm
Forum: General discussion
Topic: Do I need heatsinks and a cooling fan for the 3B+? Getting a case...
Replies: 8
Views: 293

Re: Do I need heatsinks and a cooling fan for the 3B+? Getting a case...

Generally 3B cases will work for a 3B+. The exception is those cases that act as a heatsink and touch the main chip. The chip in the 3B+ is slightly taller than the one in the 3B and a 3B case that acts as a heatsink will damage the Pi as it presses down on the chip. Most cases that don't act as a ...
by pfletch101
Wed May 01, 2019 2:11 pm
Forum: Troubleshooting
Topic: Raspberry 3b+ won't boot after connect a camera
Replies: 3
Views: 118

Re: Raspberry 3b+ won't boot after connect a camera

If you connected the camera to the CSI port while the RPi is powered on, most likely you killed your RPi (and the camera) Aside from USB, HDMI, Ethernet LAN, and audio jack, NEVER CONNECT any peripheral while the device is powered ON. Good advice, but I would go further, and recommend not connectin...
by pfletch101
Thu Apr 25, 2019 10:37 pm
Forum: Troubleshooting
Topic: RasPI 3B+ died after changing config?
Replies: 1
Views: 100

Re: RasPI 3B+ died after changing config?

Download the latest version of Raspbian and use Etcher to burn it to a new SD card, then boot the new card. It will almost certainly work fine. If you have a suitable USB card reader, plug your (logically speaking) mangled card into it, edit the copy of /etc/network/interfaces on it and reverse the ...
by pfletch101
Thu Apr 25, 2019 1:44 pm
Forum: Automation, sensing and robotics
Topic: Outdoor Pond Water Level Control / Valve
Replies: 9
Views: 484

Re: Outdoor Pond Water Level Control / Valve

But the super simple approach is two float switches. Cheap, rugged and reliable. Most float switches are based on mercury contact switches, and sometimes magnet and reed. Mercury tilt switches are accurate (reproducible) to the mm. Magnet /Reed switches tend to gain hysteresis as they age. As to th...
by pfletch101
Wed Apr 24, 2019 5:39 pm
Forum: Automation, sensing and robotics
Topic: Outdoor Pond Water Level Control / Valve
Replies: 9
Views: 484

Re: Outdoor Pond Water Level Control / Valve

…. (although why wouldn't you just use a toilet fill valve?). The OP specified that there wasn't a great deal of 'drop' between the 'full' and 'refill' levels, so you need a float to be on a short arm to get enough rotation to overcome the hysteresis of a typical level switch. Thinking about it, ho...
by pfletch101
Tue Apr 23, 2019 9:33 pm
Forum: Automation, sensing and robotics
Topic: Outdoor Pond Water Level Control / Valve
Replies: 9
Views: 484

Re: Outdoor Pond Water Level Control / Valve

If you are not using something like an ultrasound depth gauge that gives an 'analog' depth measurement, you will need two sensors, one to signal the 'full' point, and one for your chosen 'refill now' point. I would probably use a small float on a (also small) hinged arm (a miniature version of the s...
by pfletch101
Tue Apr 23, 2019 3:43 pm
Forum: Troubleshooting
Topic: How to generate PDF with PHP package
Replies: 5
Views: 88

Re: How to generate PDF with PHP package

I'm using a pi to host a local web app. The app is built on laravel and I'm using the dompdf package that can be found on github. When i run this on windows, it works perfectly. but when i transfer it over to the pi (using the latest version of raspbian, apache, and php 7,2), the page that's suppos...
by pfletch101
Tue Apr 23, 2019 2:48 pm
Forum: Beginners
Topic: Pi Zero W Static IP address
Replies: 8
Views: 261

Re: Pi Zero W Static IP address

I am going to try a workaround using the Fing app as described here https://www.raspberrypi.org/documentation/remote-access/ip-address.md which should enable me to find the IP address of the Pi if it has changed from that originally allocated. thanks for feedback I suspect that this may be the best...

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