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by JohnsUPS
Sat Jan 18, 2020 12:36 am
Forum: Automation, sensing and robotics
Topic: virgin post: need help with external pull up resistor
Replies: 13
Views: 467

Re: virgin post: need help with external pull up resistor

It appears as though you're using the 741 op amp as a comparator. Instead, I'd opt for an LM393. It probably has a higher input impedance, and is designed to work with single or dual supplies.
Also, adding hysteresis, if needed/desired, would be easier.
by JohnsUPS
Mon Jan 13, 2020 2:01 pm
Forum: Automation, sensing and robotics
Topic: Controlling Solenoid valve with Raspberry Pi 3
Replies: 58
Views: 1782

Re: Controlling Solenoid valve with Raspberry Pi 3

I've used that bridge rectifier trick before and it is an elegant way of switching an AC load. The application at the time was a motor speed controller.
by JohnsUPS
Sun Jan 12, 2020 4:17 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: 20x DS18B20 Temperature Sensors with 20M cabling each
Replies: 4
Views: 377

Re: 20x DS18B20 Temperature Sensors with 20M cabling each

What you do not want to do is connect all of this directly to GPIO pins. I have seen too many times the struggles folks go through when attempting the data line and pull up resistor scheme. Really short runs and proof of concept is fine, but I would discourage it. What should be used is a Maxim 1-wi...
by JohnsUPS
Mon Jan 06, 2020 10:17 pm
Forum: Automation, sensing and robotics
Topic: Tennis ball collector
Replies: 5
Views: 367

Re: Tennis ball collector

For your V1, just gathering the balls, I built a robot that did just that. It was limited to four billiard balls, but the mechanism could easily be adapted to tennis balls. Here is a suggestion: The gathering mechanism was simply a rotating bar that was set to about 1/8" of an inch below the top of ...
by JohnsUPS
Fri Dec 27, 2019 12:56 am
Forum: Automation, sensing and robotics
Topic: Which sensor would be most appropriate in this application?
Replies: 6
Views: 336

Re: Which sensor would be most appropriate in this application?

I don't think you'll find a simple solution to filtering out cars and leaves moving in the wind. So how about an infrared trip wire system, i.e. infra red diodes and sensors? /Mogens I was also thinking about something along this line. What came to mind was an infrared diode (or perhaps a laser dio...
by JohnsUPS
Wed Dec 18, 2019 1:18 pm
Forum: Automation, sensing and robotics
Topic: Current sensing question
Replies: 7
Views: 526

Re: Current sensing question

A couple of thoughts: Is it important to you to do this by sensing current? If so, either device you listed should work if you clamp it on the correct wire. I'd go with the fan wire (gas heater?). My second thought is do you want proof of heating happening? Or just proof that heat is being called f...
by JohnsUPS
Sat Dec 07, 2019 2:20 am
Forum: Java
Topic: How can you run a Java Applet in Raspbian Buster?
Replies: 5
Views: 557

Re: How can you run a Java Applet in Raspbian Buster?

I could get Java Web Start to work in Chromium in Raspbian Buster with this command in Bash: sudo apt install icedtea-netx At least the first demo on this page worked: https://docs.oracle.com/javase/tutorial/uiswing/examples/misc/index.html I can start some Java applets using commands similar to th...
by JohnsUPS
Sat Dec 07, 2019 1:44 am
Forum: Beginners
Topic: Connecting 5V pullup to Pi GPIO
Replies: 39
Views: 1734

Re: Connecting 5V pullup to Pi GPIO

When interfacing a Pi GPIO to anything else, I just play it safe and put in a level translator. I normally don't care about the added parts count on what is usually a single project anyway.
by JohnsUPS
Thu Dec 05, 2019 4:10 pm
Forum: Java
Topic: How can you run a Java Applet in Raspbian Buster?
Replies: 5
Views: 557

Re: How can you run a Java Applet in Raspbian Buster?

Unfortunately I am in this same predicament. There are status web pages hosted by small servers installed to monitor the HVAC in buildings where I work. These devices are old, and are using NPAPI still. I can pull them up in my Chrome browser (via a JNLP file/Java Webstart), but have had no success ...
by JohnsUPS
Tue Dec 03, 2019 12:52 am
Forum: Automation, sensing and robotics
Topic: Detecting an appliance is in use
Replies: 30
Views: 1321

Re: Detecting an appliance is in use

I made a monitor for my sump pump that simply counts the number of times that the pump has energized. All that was necessary was to connect a small step-down transformer across the motor leads. This pump has two cords coming from it - one for the pump and one for the switch, so the motor connections...
by JohnsUPS
Tue Nov 19, 2019 10:50 pm
Forum: Automation, sensing and robotics
Topic: Smart Coffee Machine Pump Controlled by Raspberry Pi & HC-SR04 Ultrasonic Sensor
Replies: 3
Views: 304

Re: Smart Coffee Machine Pump Controlled by Raspberry Pi & HC-SR04 Ultrasonic Sensor

Great project!

You could get a reverse osmosis filter setup and remove the bottle altogether. No pump needed either.....
by JohnsUPS
Mon Nov 18, 2019 11:56 pm
Forum: Automation, sensing and robotics
Topic: How to turn on Multiple TVs using a raspberry Pi?
Replies: 4
Views: 338

Re: How to turn on Multiple TVs using a raspberry Pi?

If the TVs are on a network, they may respond to a wake on LAN broadcast..... Otherwise, (as was previously mentioned) it would be perfectly feasible to configure a Pi with an IR LED connected to a GPIO pin and modulated with the "turn on" remote control code bit banged by a snippet of code. For tha...
by JohnsUPS
Thu Nov 14, 2019 1:22 am
Forum: Advanced users
Topic: Is it possible for RaspberryPi 3 B+ to power a 6V device
Replies: 14
Views: 723

Re: Is it possible for RaspberryPi 3 B+ to power a 6V device

I have contemplated doing this myself, but my solution was to connect an optoisolator across the switch of the remote. This way, all that needs to be done is to drive the LED of the optoisolator from a GPIO pin. Any general purpose opto should work, so long as the current requirements of the LED are...
by JohnsUPS
Wed Nov 06, 2019 2:54 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: DS18b20 and Relay
Replies: 4
Views: 954

Re: DS18b20 and Relay

What transistor are you using? Not all transistors have the center pin as the base.....
by JohnsUPS
Sun Nov 03, 2019 8:58 pm
Forum: Other projects
Topic: Messure AC current
Replies: 5
Views: 780

Re: Messure AC current

When working with mains voltages, please observe all the applicable precautions first....... To measure anything off the mains, you should really use a transformer for isolation. For measuring current, you could go with something like this: https://www.amazon.com/HiLetgo-Current-Ammeter-TA12-100-Ard...
by JohnsUPS
Sun Nov 03, 2019 12:21 am
Forum: Automation, sensing and robotics
Topic: Flow meter question
Replies: 4
Views: 774

Re: Flow meter question

I looked at the data sheet for the flow meter, and there is a 10k pullup on the open collector output to the V+ pin. Because the data sheet lists the working voltage as 5 - 24 VDC, the data line will be pulled up very close to 5V (if the meter is powered from 5V). The GPIO pins cannot tolerate more ...
by JohnsUPS
Fri Oct 25, 2019 1:37 pm
Forum: Advanced users
Topic: Multiple DS18B20 temperature sensors
Replies: 36
Views: 22060

Re: Multiple DS18B20 temperature sensors

I assume this has to do with the fact that the temperature sensors are on a long wire. I have them now on a 5 wire direct bury cable. Red carries the positive, black negative and yellow, white and orange carry a signal back. Each signal has its own resistor and gpio. The cable is about 50 ft long a...
by JohnsUPS
Fri Oct 25, 2019 1:01 pm
Forum: Advanced users
Topic: Multiple DS18B20 temperature sensors
Replies: 36
Views: 22060

Re: Multiple DS18B20 temperature sensors

I do not understand your last comment from your setup..."the data line comes back to a driver chip". I understand the single wire setup but what is your driver chip? Do you mean the internal PI I2C? In the temperature measurement setup that I have deployed, the data line does not come back to a GPI...
by JohnsUPS
Thu Oct 24, 2019 1:24 am
Forum: Advanced users
Topic: Multiple DS18B20 temperature sensors
Replies: 36
Views: 22060

Re: Multiple DS18B20 temperature sensors

I assume this has to do with the fact that the temperature sensors are on a long wire. I have them now on a 5 wire direct bury cable. Red carries the positive, black negative and yellow, white and orange carry a signal back. Each signal has its own resistor and gpio. The cable is about 50 ft long a...
by JohnsUPS
Mon Oct 21, 2019 11:59 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: One wire DS18b20 sensors disconnected when reading too fast
Replies: 8
Views: 1580

Re: One wire DS18b20 sensors disconnected when reading too fast

Thank you both for your valuable tips. I made some further debbuging. With one sensor at a time running for at least 30mins reading the temperature every 5 seconds. One of my four sensors dies after circa 10 minutes. I haven'm made another test run to confirm or another run with those remaining 3 t...
by JohnsUPS
Mon Oct 21, 2019 11:47 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: One wire DS18b20 sensors disconnected when reading too fast
Replies: 8
Views: 1580

Re: One wire DS18b20 sensors disconnected when reading too fast

It sounds like you are using a water proof ds18b20 sensor, there are many low quality/factory seconds being sold on line on various line on sales sites, these often fail after some use or randomly , I have experienced this myself. You could try testing your setup using just the ds18b20 chip obtaine...
by JohnsUPS
Thu Oct 17, 2019 3:12 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: DS18B20 Max Distance
Replies: 44
Views: 51466

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: 8
Views: 1580

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: 20
Views: 997

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: 20
Views: 997

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...

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