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by JohnsUPS
Thu Oct 17, 2019 3:12 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: DS18B20 Max Distance
Replies: 44
Views: 46992

Re: DS18B20 Max Distance

@JohnsUPS Hello, first of all let me thank you for your careful post. I'm sure it has provided countless people (like myself) with inspiration on how to extend the scale of their 1-wire designs... I have a couple of questions: First, I was quite surprised to see how you are using the CAT6 wire, bun...
by JohnsUPS
Thu Oct 17, 2019 1:45 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: One wire DS18b20 sensors disconnected when reading too fast
Replies: 4
Views: 97

Re: One wire DS18b20 sensors disconnected when reading too fast

If your sensors are located in such a manner that running one cable and daisy chaining them together isn't practical, you can run each sensor back to a separate GPIO pin. However, each pin must have its own pullup resistor to 3.3v. This will eliminate the star topology that was created when the data...
by JohnsUPS
Sat Oct 12, 2019 1:26 am
Forum: Beginners
Topic: Trouble reading DS18B20 one wire through 16 relay board on RPi
Replies: 14
Views: 372

Re: Trouble reading DS18B20 one wire through 16 relay board on RPi

Thanks for the post, I have six pieces of ULN2803A chips, will that work? Or I have to get the Dallas DS2482-800 ? For either, would you mind to show me how do I connect it with the one wire sensor and the pi? The ULN2803A driver and the DS2482-800 driver are chips with completely different target ...
by JohnsUPS
Thu Oct 10, 2019 10:37 pm
Forum: Beginners
Topic: Trouble reading DS18B20 one wire through 16 relay board on RPi
Replies: 14
Views: 372

Re: Trouble reading DS18B20 one wire through 16 relay board on RPi

You probably shouldn't attempt to switch the sensors on and off. They will be perfectly happy running all the time. Besides, if the sensor is off, you will miss any temperature swings that may have happened. The relay board isn't needed. If you want to run 32 sensors, no problem. The way I would tac...
by JohnsUPS
Mon Sep 09, 2019 2:00 am
Forum: Troubleshooting
Topic: Help with 4-20mA and Raspberry Pi 3B+
Replies: 6
Views: 316

Re: Help with 4-20mA and Raspberry Pi 3B+

If you still want to use the current to voltage converter board, then you don't need a resistor in series with the output of the sensor as the board provides this series resistor for you. The board is expecting to be connected to a current source directly. It appears as though you're making sure tha...
by JohnsUPS
Sat Sep 07, 2019 5:04 am
Forum: Troubleshooting
Topic: Help with 4-20mA and Raspberry Pi 3B+
Replies: 6
Views: 316

Re: Help with 4-20mA and Raspberry Pi 3B+

You didn't provide any details about the pressure transmitter. I am referencing this two wire pressure sensor wiring diagram, using the "4-20ma Output Wiring Diagram with Integral Cable", which appears to be wired similarly to what you have shown: https://cdn.automationdirect.com/static/specs/prosen...
by JohnsUPS
Tue Sep 03, 2019 3:18 am
Forum: Automation, sensing and robotics
Topic: Car clutch sensor
Replies: 3
Views: 256

Re: Car clutch sensor

Other than tapping off an existing switch (such as the one tied to the cruise control), you could add your own switch to the clutch pedal. Where the switch resides would depend on how the clutch is set up. The switch could either reside under the dash by the pedal, or if there is a lever somewhere (...
by JohnsUPS
Fri Aug 30, 2019 12:26 am
Forum: Other projects
Topic: Pushbutton multiple inputs
Replies: 12
Views: 516

Re: Pushbutton multiple inputs

So basically you are saying if the button was wired to 3.3V and GPIO from the beginning with PD resistor enabled via SW, I should not see random inputs triggered on that pin? Not exactly. With the way you stated that this push button is wired, with one side going to +5V, then pushing the button wil...
by JohnsUPS
Thu Aug 29, 2019 11:35 pm
Forum: General discussion
Topic: pics - how are you using your Pi?
Replies: 18
Views: 1122

Re: pics - how are you using your Pi?

Recent project....Temperature and rooftop data center chiller monitor.

Image
by JohnsUPS
Tue Aug 27, 2019 10:13 pm
Forum: Automation, sensing and robotics
Topic: Motor Sensing Circuit help
Replies: 5
Views: 507

Re: Motor Sensing Circuit help

Does the motor operate at full on and full off or does it operate at variable speeds? Knowing the answers to those questions will help to identify how sensitive the sensing circuit needs to be. Because the output of the CT transformer is 0-1V @ 0-15A, you could feed it to a comparator circuit, but n...
by JohnsUPS
Fri Aug 09, 2019 1:30 am
Forum: Other projects
Topic: How to read 4-20mA signal input
Replies: 20
Views: 26517

Re: How to read 4-20mA signal input

What can also be used to keep the current loop isolated while still being able to precisely read the voltage across the scaling resistor used in the loop is a switched capacitor building block, like the LT6943: https://www.analog.com/media/en/technical-documentation/data-sheets/6943f.pdf The output ...
by JohnsUPS
Tue Aug 06, 2019 10:18 pm
Forum: Automation, sensing and robotics
Topic: Phone hang-up sensor
Replies: 9
Views: 424

Re: Phone hang-up sensor

I wasn't able to see the pic, but what could also be used is a reed relay within the phone, actuated by a magnet attached to the receiver.
by JohnsUPS
Fri Aug 02, 2019 11:45 am
Forum: Advanced users
Topic: Multiple DS18B20 temperature sensors
Replies: 27
Views: 17967

Re: Multiple DS18B20 temperature sensors

The estimated cable length for the sensors: BME280: temp_air = 5 inch max (~ 0.13m) DS18B20: temp_topsoil = 6 ft (~ 1.8m) DS18B20: temp_frost = 9 ft (~2.7m) DS18B20: temp_water = 12 ft (~ 3.7m) DS18B20: temp_deepwater = 50 ft (~ 15.2m) I have read up on the linear, stubbed and star configurations. ...
by JohnsUPS
Mon Jul 29, 2019 1:46 am
Forum: Wanted
Topic: DS18B20 Sensor
Replies: 4
Views: 2600

Re: DS18B20 Sensor

If you're inclined to order a bunch of these, I would strongly suggest that you order them from a reputable dealer like Digi-Key, Mouser or Jameco who surely source directly from Maxim/Dallas. I ordered a couple of ten packs from China (from two different vendors), and each time received parts that ...
by JohnsUPS
Wed Jul 24, 2019 12:50 am
Forum: Automation, sensing and robotics
Topic: Electronic chess board and identifying specific pieces
Replies: 8
Views: 545

Re: Electronic chess board and identifying specific pieces

Possibly a bar code or Q code on the bottom to identify each piece......
by JohnsUPS
Sun Jul 07, 2019 3:00 am
Forum: Automation, sensing and robotics
Topic: which sensor to use for a coffee maker
Replies: 8
Views: 394

Re: which sensor to use for a coffee maker

It appears as though an appropriately small micro switch fastened to the "wall" shown on the left side of the picture may do it. The metal actuation arm of the micro switch could be bent to correctly contact the vertical brass (?) cylinder towards the top to maximize the throw of the contacting arm....
by JohnsUPS
Mon Jul 01, 2019 1:58 am
Forum: Other projects
Topic: How to read 4-20mA signal input
Replies: 20
Views: 26517

Re: How to read 4-20mA signal input

When you say "4-20ma" signal, that is usually referring to serial communication over a current loop, but as was pointed out, could also be an analog signal that is within that range. If it is current loop communications that you are referring to, the below may be of help...... If you prefer to roll ...
by JohnsUPS
Sat Jun 29, 2019 2:20 am
Forum: Automation, sensing and robotics
Topic: Monitoring HVAC
Replies: 2
Views: 472

Re: Monitoring HVAC

From what you have said, it sounds like all you want to do is monitor the states of various 24VAC supply/signal lines that run throughout your HVAC system. To reiterate what rpdom had stated, the Pi GPIOs can't accept a 5V signal, it can't be more than 3.3V. A relay is a good solution, but there is ...
by JohnsUPS
Tue Jun 25, 2019 3:14 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: 1-Wire Ds18B20 temperature sensor disappearing when over 60°C
Replies: 7
Views: 850

Re: 1-Wire Ds18B20 temperature sensor disappearing when over 60°C

When it comes to sending signalling over a long wire, the length of the wire can influence how quickly a voltage transition will appear at the other end. The topology, type of wire and the characteristics of the wire used will influence this. As it turns out, the 1-wire protocol is sensitive to sign...
by JohnsUPS
Sat Jun 22, 2019 12:55 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Water proof reliable temperature probe
Replies: 2
Views: 589

Re: Water proof reliable temperature probe

The sensor that you have is probably a knock-off/fake. There are a lot of them out there, especially if ordered from China. I have run into this issue myself. Do yourself a favor and spend a dollar or two more on sensors from a reliable seller, such as Digi-Key or Mouser. These larger companies sour...
by JohnsUPS
Sat Jun 22, 2019 12:47 pm
Forum: Beginners
Topic: How to make the GPIO connections more robust
Replies: 10
Views: 1129

Re: How to make the GPIO connections more robust

As a general rule when I'm interfacing to the GPIO pins, I follow the pin with some sort of buffer, such as a transistor or inverter. The choice of buffer mainly depends on what is ultimately being driven. The buffer circuitry helps to protect the Pi in the case of an "oops" or line transient and ca...
by JohnsUPS
Fri Jun 21, 2019 2:05 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: 1-Wire Ds18B20 temperature sensor disappearing when over 60°C
Replies: 7
Views: 850

Re: 1-Wire Ds18B20 temperature sensor disappearing when over 60°C

Are your sensors wired in a star topology (one wire per sensor back to the Pi), or are they all strung out along a single length of cable? If each sensor does have its own cable, try disconnecting two of the sensors (at the Pi - not just removing them from the end) and then see if things fail above ...
by JohnsUPS
Fri Jun 21, 2019 1:21 am
Forum: Automation, sensing and robotics
Topic: multiple DS18B20 no longer showing up
Replies: 4
Views: 536

Re: multiple DS18B20 no longer showing up

I have narrowed it down to somewhere during or after the cable run, because it works fine when I use a sensor connected directly to the GPIO pins. Bear in mind that if the sensor is connected directly to the GPIO pins, the connections are much shorter, and therefore cable characteristics (resistanc...
by JohnsUPS
Sat Jun 15, 2019 6:54 pm
Forum: Automation, sensing and robotics
Topic: multiple DS18B20 no longer showing up
Replies: 4
Views: 536

Re: multiple DS18B20 no longer showing up

My suspicion is that the data line is seeing reflections due to the longer length of wire now connecting the sensors. Take a look at this post - it may offer assistance in solving the problem: https://www.raspberrypi.org/forums/viewtopic.php?t=36163 and https://www.raspberrypi.org/forums/viewtopic.p...
by JohnsUPS
Tue Jun 11, 2019 9:31 pm
Forum: Advanced users
Topic: RPI Ethernet Gadget intermediary.
Replies: 4
Views: 413

Re: RPI Ethernet Gadget intermediary.

It may be more practical to insert a PC with dual Ethernet ports running Wireshark in the middle....

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