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by JohnsUPS
Fri Aug 09, 2019 1:30 am
Forum: Other projects
Topic: How to read 4-20mA signal input
Replies: 20
Views: 23536

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: 235

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: 16491

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: 472

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: 422

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: 312

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: 23536

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: 376

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: 744

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: 542

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: 1078

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: 744

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: 498

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: 498

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: 358

Re: RPI Ethernet Gadget intermediary.

It may be more practical to insert a PC with dual Ethernet ports running Wireshark in the middle....
by JohnsUPS
Mon Jun 03, 2019 11:16 pm
Forum: Beginners
Topic: How to hookup battery pack to a servo?
Replies: 8
Views: 292

Re: How to hookup battery pack to a servo?

... I just randomly start soldering wires together lol Don't do that. It's the fastest way to destroy your Pi. You need to draw a diagram of the breadboard wiring that works, then transfer that to a stripboard layout (or whatever other system you choose). Do the above...........^^^ You may find tha...
by JohnsUPS
Wed May 22, 2019 11:55 pm
Forum: Troubleshooting
Topic: "Blips" in ADS1115 reading used with Raspberry Pi 3B
Replies: 1
Views: 152

Re: "Blips" in ADS1115 reading used with Raspberry Pi 3B

You may want to bump up the ADS1115_CONVERSIONDELAY from 8ms to about 10ms. What may be happening is your code is trying to read the chip prior to the completion of the conversion. This happened to me recently, and going to 10ms solved the problem. Bumping this value may provide more stability in th...
by JohnsUPS
Wed May 22, 2019 11:15 pm
Forum: Beginners
Topic: Need to operate 12 servos at a range of 1200 yards
Replies: 9
Views: 518

Re: Need to operate 12 servos at a range of 1200 yards

Seems like wireless would be the way to go. I have had good luck with these: https://www.amazon.com/EnGenius-Technologies-EnStation5-AC-Outdoor-Wireless/dp/B073H5KSSJ/ref=sr_1_fkmrnull_2?keywords=engenius+access+point+ac867&qid=1558566532&s=gateway&sr=8-2-fkmrnull I have deployed a set (for remote b...
by JohnsUPS
Wed May 15, 2019 1:18 am
Forum: Automation, sensing and robotics
Topic: My temp sensor ds18b20 doesn't seems accurate
Replies: 14
Views: 779

Re: My temp sensor ds18b20 doesn't seems accurate

I have had this happen to me also. Where were the sensors purchased? I have about 30 of these sensors. 10 each were purchased from three different vendors. Two of the vendors were of Chinese origin, and the other was Mouser. After the first order of 10, I realized they were not calibrated because th...
by JohnsUPS
Wed May 08, 2019 5:25 pm
Forum: Beginners
Topic: Will a power supply with a higher amp-age work with the pi?
Replies: 22
Views: 14454

Re: Will a power supply with a higher amp-age work with the pi?

It is like the ampere-hour capacity of a battery and is not applicable to the discussion in this thread. I agree, that is more correct. Reservoir was probably not the best choice of words. Current sourcing capability. I also agree about the water flow analogy being useful, but only to a point. I ge...
by JohnsUPS
Wed May 08, 2019 10:29 am
Forum: Beginners
Topic: Will a power supply with a higher amp-age work with the pi?
Replies: 22
Views: 14454

Re: Will a power supply with a higher amp-age work with the pi?

A lot of that is incorrect. The size of the reservoir is not the "amperage capability". The current is not the "actual water" but the rate of flow of the water. I respectfully disagree. Note that I said "as it applies to this discussion". Sure, electrons (or holes, depending on the theory you subsc...
by JohnsUPS
Wed May 08, 2019 12:39 am
Forum: Beginners
Topic: Will a power supply with a higher amp-age work with the pi?
Replies: 22
Views: 14454

Re: Will a power supply with a higher amp-age work with the pi?

Another way to look at the electricity and water comparison is this: Voltage is the water pressure produced by a water pump. Amperage capability (as it applies in this discussion) is the size of the reservoir that feeds the water pipe. Currrent is the actual water. Resistance is related to the diame...
by JohnsUPS
Sun May 05, 2019 1:17 am
Forum: General discussion
Topic: Raspberry Pi Zero W.....for a pub
Replies: 6
Views: 463

Re: Raspberry Pi Zero W.....for a pub

If your pub has the need for cold food storage, then the Pi could be used to periodically take temperature readings to satisfy the inspectors. This is more mechanical, but a machine that could tip a bottle and pour a shot would make for interesting conversation. A reaction timer.....light (LED or wh...
by JohnsUPS
Sat May 04, 2019 5:07 am
Forum: Automation, sensing and robotics
Topic: Pressure logging project
Replies: 6
Views: 418

Re: Pressure logging project

If you go with the 625 transducer with the 4 - 20ma output, it is to your advantage that it has a current source output. Current outputs are inherently less noisy and can run fair distances in an electrically noisy environment. This is good, especially if you're connecting it to an ADC. You can easi...
by JohnsUPS
Thu May 02, 2019 1:51 pm
Forum: HATs and other add-ons
Topic: Sensors maximum length
Replies: 6
Views: 490

Re: Sensors maximum length

When it comes to the DS18B20 temperature sensors with regards to wiring length, you may want to check this thread:
viewtopic.php?t=36163

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