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by JohnsUPS
Fri Jan 25, 2019 2:15 pm
Forum: General discussion
Topic: Power Supply - Radio Interference
Replies: 38
Views: 2098

Re: Power Supply - Radio Interference

To see if the PSU was faulty, I plugged the Pi into another brand new, official Pi PSU. Loud buzzing still present. On a whim, I dug out a couple of non-Pi 5v power adapters and tried them. The Pi booted and the buzzing was gone. Were the "non-Pi 5v" power supplies of a transformer type or were the...
by JohnsUPS
Fri Jan 25, 2019 2:52 am
Forum: General discussion
Topic: Bouncing an idea.(wire power through spare ethernet wires)
Replies: 8
Views: 527

Re: Bouncing an idea.(wire power through spare ethernet wires)

If the cable lengths are going to be rather short (OP mentioned ~12" or so), then voltage drop won't be a problem. The Pi will work just fine on 10/100 Ethernet, which uses wires 1, 2, 3 & 6 for transmit & receive. If you want to wire your own "poor man's POE" as I like to call it, just use the rema...
by JohnsUPS
Thu Jan 24, 2019 1:19 am
Forum: Beginners
Topic: Detect electrical current of external device
Replies: 13
Views: 1036

Re: Detect electrical current of external device

Correct. I was thinking DC when I composed that, but later realized my mistake. I edited my post to remove the reverse biased diode sentence, but apparently you responded before the edit went into effect. Also, I listed the specific transient supressor/TranZorb (in a previous post) that I would have...
by JohnsUPS
Wed Jan 23, 2019 10:43 pm
Forum: Beginners
Topic: Detect electrical current of external device
Replies: 13
Views: 1036

Re: Detect electrical current of external device

With relays connected as I have previously described, there will not be any back emf issues at all. This is because a physical contact switch (doorbell button) is activating the relay coils and not a semiconductor of some sort. Any back emf will be across wiring that is already handling the solenoid...
by JohnsUPS
Tue Jan 22, 2019 11:52 pm
Forum: Beginners
Topic: Detect electrical current of external device
Replies: 13
Views: 1036

Re: Detect electrical current of external device

+1. It will be the cheapest, smallest and most reliable solution. A lot of that depends on how much fabricating the OP is planning on doing. Smallest, probably. Once again, that would depend upon the construction technique used. I suggested relays mainly to keep things simple. I don't know about th...
by JohnsUPS
Tue Jan 22, 2019 6:59 pm
Forum: Beginners
Topic: Detect electrical current of external device
Replies: 13
Views: 1036

Re: Detect electrical current of external device

What I would do in this situation is to use a relay (or two - more about that in a moment). Minimal hardware is the goal here.. First, you need to determine what voltage the solenoids within the doorbell operates at. In my house it is 24VAC. Either look at the doorbell transformer (voltage probably ...
by JohnsUPS
Sun Jan 20, 2019 9:54 pm
Forum: Other projects
Topic: Question about powering home automation system
Replies: 4
Views: 701

Re: Question about powering home automation system

I believe you're overthinking the PoE aspect of this. True, PoE voltage (for IEEE standard 802.3af) is 48 VDC, and is designed to be able to deliver about 12.95 watts of power (minus voltage drops) to the end load. 13 watts of power is more than enough. The standard Pi supply delivers ~2 amps @ 5 vo...
by JohnsUPS
Fri Jan 18, 2019 1:12 pm
Forum: Automation, sensing and robotics
Topic: I2C to 1-Wire RPi Zero - Solar Hot Water Heater Build
Replies: 6
Views: 922

Re: I2C to 1-Wire RPi Zero - Solar Hot Water Heater Build

You will probably have to make your own breakout board for the DS2482. This is what I did. Not difficult. The easiest package to work with is the 8-SOIC package, so an adapter board that will go from the 8-SOIC foot print to a DIP package 0.1" spacing (if you're not making your own PCB) is probably ...
by JohnsUPS
Thu Jan 17, 2019 4:05 am
Forum: Automation, sensing and robotics
Topic: Joining multiple DS18B20 sensors
Replies: 13
Views: 1738

Re: Joining multiple DS18B20 sensors

Prarietech, The driver chip is at the end of the line, near the Pi. In my application, it is in the same project enclosure as the Pi. I2C is a protocol that isn't designed to work over distance. It was developed for inter-chip communication, implying that the runs are generally short - on the order ...
by JohnsUPS
Wed Jan 16, 2019 12:14 pm
Forum: Automation, sensing and robotics
Topic: Joining multiple DS18B20 sensors
Replies: 13
Views: 1738

Re: Joining multiple DS18B20 sensors

I'll try tp post a schematic. Can't do it right now though. When I was referring to "driving the wire", I am referring to the long length of wire from the driver to the sensors. The Pi only talks to the driver chip (DS2482-100 in this case) using I2C through a couple of level shifters, as the chip i...
by JohnsUPS
Wed Jan 16, 2019 2:27 am
Forum: Automation, sensing and robotics
Topic: Joining multiple DS18B20 sensors
Replies: 13
Views: 1738

Re: Joining multiple DS18B20 sensors

Prarietech, yes, the DS2482 is driving the line the whole distance. Also keep in mind that some of the time the driver chip is driving the wire, and sometimes the DS18B20 is driving the wire, so the devices at each end have to be able to drive the whole distance at some point in time. This is why th...
by JohnsUPS
Sun Jan 13, 2019 7:51 pm
Forum: Automation, sensing and robotics
Topic: Joining multiple DS18B20 sensors
Replies: 13
Views: 1738

Re: Joining multiple DS18B20 sensors

You want to wire all of the sensors in parallel. This will avoid the star topology, and you can go quite a distance. I currently have an installation of five DS18B20 sensors along 369 feet of CAT6, and they are working flawlessly. Wired like so: At each sensor, there is a 10ufd tantalum capacitor ac...
by JohnsUPS
Sun Jan 13, 2019 6:54 pm
Forum: General discussion
Topic: Solder won't melt on pins when desoldering
Replies: 7
Views: 697

Re: Solder won't melt on pins when desoldering

Desoldering can be tricky, especially when the pin you're trying to desolder is connected to a ground plane of the board. The heat-sinking effect of the larger copper area can cause problems. As rpdom mentioned, flowing some regular 60/40 solder can help. I've done a lot of desoldering (it is how I ...
by JohnsUPS
Sun Jan 13, 2019 6:45 pm
Forum: General discussion
Topic: poe rackmountable switch
Replies: 2
Views: 216

Re: poe rackmountable switch

Any POE network switch that is compatible with IEEE standards 802.3af (PoE) or 802.3at (PoE+) will work.
by JohnsUPS
Mon Jan 07, 2019 2:37 am
Forum: Automation, sensing and robotics
Topic: Relay Line out voltage causing voltage on line in
Replies: 31
Views: 2237

Re: Relay Line out voltage causing voltage on line in

Also don't forget the reversed biased diode across the coil of the relay. This wasn't shown in the schematic. Standard practice is to locate the diode as close to the relay coil as possible. The ULN chip has these built in, but they are located on the chip, and I wouldn't depend on them......
by JohnsUPS
Tue Jan 01, 2019 11:59 pm
Forum: Automation, sensing and robotics
Topic: DS18B20 randomly missing connection
Replies: 3
Views: 897

Re: DS18B20 randomly missing connection

The mixed topology wiring is part of the problem here. Per Maxim and other testimonials that I have read, the 1-Wire protocol does not like a star topology. My suspicion is that it isn't very tolerant to reflections on the line, and with a star topology these reflections are going to happen at sligh...
by JohnsUPS
Tue Jan 01, 2019 11:27 pm
Forum: Automation, sensing and robotics
Topic: Relay Line out voltage causing voltage on line in
Replies: 31
Views: 2237

Re: Relay Line out voltage causing voltage on line in

What is happening is that you are getting coupling from the mains back to the input from within the relay, and this is largely the result of the high voltage AC connection. Bear in mind that the input impedance on your multimeter is very high, and that any coupling will show up because there is no l...
by JohnsUPS
Sat Dec 22, 2018 12:23 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Backlight Control on Waveshare 5" Touchscreen
Replies: 23
Views: 14777

Re: Backlight Control on Waveshare 5" Touchscreen

I'll try to post my schematic.... My standard practice is to buffer a GPIO pin with a small value resistor, then to the base of a transistor. This is done to protect the GPIO pin. The transistor then does the heavy lifting for whatever I'm wanting to drive. https://i.pinimg.com/originals/6a/cf/2e/6a...
by JohnsUPS
Mon Dec 10, 2018 3:19 am
Forum: Automation, sensing and robotics
Topic: How to power and read multiple DS18B20 temperature sensors
Replies: 18
Views: 8796

Re: How to power and read multiple DS18B20 temperature sensors

Have you considered using a 1 wire driver chip? I am using the DS2482-100. It is connected to the PI via I2C. The chip is powered from 5v, and there are level shifters in the two I2C lines to the PI. The chip also protects the GPIO line/PI from transients from the outside world. The 5v supply to the...
by JohnsUPS
Mon Dec 10, 2018 2:24 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Backlight Control on Waveshare 5" Touchscreen
Replies: 23
Views: 14777

Re: Backlight Control on Waveshare 5" Touchscreen

I bought an inexpensive 5" LCD panel for a recent project, and I needed a way to turn the backlight on and off. The display had an on/off switch on it, so instead of cutting traces, I added a couple of mosfets. I measured the backlight currrent, which was ~107ma. The mosfets I used were rated higher...
by JohnsUPS
Mon Oct 08, 2018 11:10 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: DS18B20 Max Distance
Replies: 44
Views: 48837

Re: DS18B20 Max Distance

Just an update to my earlier post about the data center temperature monitor. The monitor has been installed, and everything is working perfectly. I wanted to share some of the installation details, as this installation technique is now proven to work in an electrically noisy environment and should b...
by JohnsUPS
Sun Sep 09, 2018 12:32 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: DS18B20 Max Distance
Replies: 44
Views: 48837

Re: DS18B20 Max Distance

The setup is still working perfectly (and has been for weeks now), but a 1 wire bus master is not a "booster". It is just a proper driver. If someone has a distance requirement, using a driver is the logical place to start. The common method I see is by using a GPIO pin with a pullup, which may be O...
by JohnsUPS
Tue Aug 14, 2018 12:32 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: favorite replacement for 8-channel Bi-directional Logic Level Converter - TXB0108
Replies: 3
Views: 1168

Re: favorite replacement for 8-channel Bi-directional Logic Level Converter - TXB0108

In the past, I purchased several 4 bit bidirectional level shifters, all nice surface mount assemblies, but they were not very reliable. Instead, I have opted for a larger through-hole solution. It may be a bit more work if you need to shift many lines, but I have found the simple level shifter made...
by JohnsUPS
Sat Jul 07, 2018 2:28 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: DS18B20 Max Distance
Replies: 44
Views: 48837

Re: DS18B20 Max Distance

JohnsUPS That's are very good news, please check you PM inbox. BR, YV1HX, I wanted to post my test results because the search results I got when researching the distance were not too inspiring. I am the type that will test something like this for myself. Because I know that my previous post is sear...
by JohnsUPS
Fri Jul 06, 2018 3:15 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: DS18B20 Max Distance
Replies: 44
Views: 48837

Re: DS18B20 Max Distance

I am in the process of building a data center temp monitor for my work, and have settled on the DS18B20's for the sensors. However, I was concerned about the 1 wire protocol distance, until tonight when I was able to test this. I have five sensors at the end of 470 feet (143 meters) of Cat6 working ...

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