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by JohnsUPS
Fri Apr 10, 2020 7:51 pm
Forum: General discussion
Topic: Raspberry Pi 3 with light sensor and LED!
Replies: 4
Views: 426

Re: Raspberry Pi 3 with light sensor and LED!

There should really be a comparator on the light sensor (how I would do it), but an easier/simpler way in this case would be to put a potentiometer (at least 10k or so) in series with the light sensor. The trigger point will then be the logic threshold of the GPIO pin (which is not ideal), but shoul...
by JohnsUPS
Thu Apr 09, 2020 5:40 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Use GPIO for Water tank level
Replies: 4
Views: 373

Re: Use GPIO for Water tank level

Another way to do this if you don't need much accuracy is to take a string of reed relays and mount them into a watertight tube. One end of each relay would be connected together and connected to ground. Each of the other relays would be connected to an individual GPIO pin. A floating circular magne...
by JohnsUPS
Sun Mar 29, 2020 10:29 pm
Forum: General discussion
Topic: How to create a static ip address
Replies: 5
Views: 482

Re: How to create a static ip address

It might be easier/more convenient to create a reservation on your router instead. You will need to know the MAC address of the Pi (either the wired or the wireless MAC depending on how you're connecting). The router will then always hand out that particular IP address to the device with the corresp...
by JohnsUPS
Sun Mar 29, 2020 1:31 pm
Forum: General discussion
Topic: Water tank level monitoring. Skill level required?
Replies: 10
Views: 961

Re: Water tank level monitoring. Skill level required?

Many years ago, I ran a hemodialysis center that had a 1K gal. storage tank for pure water from an RO machine that ran all night. It used a set of reed relays inside a sealed long poly tube, activated by a donut shaped magnet that rode on the outside of the poly tube with a float. An RPi could easi...
by JohnsUPS
Sun Mar 29, 2020 1:20 pm
Forum: General discussion
Topic: Rpi 3B+: how cold can it still opperate?
Replies: 21
Views: 881

Re: Rpi 3B+: how cold can it still opperate?

ok, thank you. i will proceed with the project, and see what happens. if worst comes to worst, i could try the XBEE option. ~Travis Keep in mind that the Xbee would have to function down to that temperature also. If the generator is near the house, then just run the appropriate wiring into the hous...
by JohnsUPS
Mon Mar 23, 2020 11:50 pm
Forum: General discussion
Topic: Brainstorming using the raspberry pi to make a generic respirator
Replies: 13
Views: 1510

Re: Brainstorming using the raspberry pi to make a generic respirator

On the topic of ventilators, I was wondering if a sleep apnea machine could be retrofitted in some way.......just a thought...
by JohnsUPS
Sun Mar 22, 2020 3:40 am
Forum: Other projects
Topic: Wiring Pi to Magnetic Lock and Relay Switch
Replies: 4
Views: 345

Re: Wiring Pi to Magnetic Lock and Relay Switch

Be careful with the lock. My workplace has many doors secured with these magnetic holds. Properly installed, they will hold 600lbs, so the magnetic field is considerable. Over time, the inductive kickback of the coils in the holding devices causes damage to the relay contacts that actuate them. I pe...
by JohnsUPS
Thu Mar 19, 2020 10:43 pm
Forum: General discussion
Topic: Problem with GPIO and relay
Replies: 22
Views: 1249

Re: Problem with GPIO and relay

Yeah, as a rule I use the GPIO pins as a source of logic switching only, and ALWAYS buffer the pin in some way or another. In the case of the diagram that pcmanbob posted, it is the combination of the resistor and transistor.
I am wonder how many times pcmanbob has posted this schematic.....
by JohnsUPS
Thu Mar 12, 2020 11:17 am
Forum: Beginners
Topic: Thank You :-)
Replies: 8
Views: 628

Re: Thank You :-)

Yes - Kudos.

I obtained an extra Pi at work and repurposed it as an additional desktop (have it displaying a web page generated by another Pi incidentally), and it is much snappier at displaying web content than some of my other desktop PC's :-)
by JohnsUPS
Wed Mar 11, 2020 10:42 am
Forum: General discussion
Topic: Control LED
Replies: 3
Views: 312

Re: Control LED

by JohnsUPS
Sun Mar 08, 2020 10:13 pm
Forum: Automation, sensing and robotics
Topic: Sensors for system at work
Replies: 16
Views: 1232

Re: Sensors for system at work

Here is another idea - Because the biscuits are on a V grooved conveyor belt (going by the pic that was posted), doing a make-break beam type of sensor would appear to be difficult to implement, as going straight across the conveyor does not appear to be an option. If I were to attempt this, I would...
by JohnsUPS
Tue Mar 03, 2020 12:25 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: MCP3008 voltage values are 2x larger than expected
Replies: 6
Views: 517

Re: MCP3008 voltage values are 2x larger than expected

Have you tried applying a constant DC voltage to validate the ADC and your code? If that comes back as accurate, then your readings are being based on how the ADC is seeing the sine wave. Maybe you need to look into synchronizing the ADC reads with a zero crossing detector (with delay to catch the p...
by JohnsUPS
Tue Mar 03, 2020 2:28 am
Forum: Beginners
Topic: Accessing School Wifi [solved]
Replies: 11
Views: 621

Re: Accessing School Wifi

In order to access the school Wi-Fi you need to know the Ip address of your school Wi-fi in the first hand. The IP address like ] may be the access point of the router. So in order to access your school Wi-Fi you need to find the correct the router Ip first. Then proceed. The above isn't correct. Y...
by JohnsUPS
Mon Mar 02, 2020 11:56 am
Forum: Beginners
Topic: Is it safe to build circuit after boot?
Replies: 16
Views: 1109

Re: Is it safe to build circuit after boot?

My philosophy has always been to power down first, [make changes] and power up last. Be sure to observe the proper power down procedures - don't just pull the connector or flip the switch. This will become a habit after a while, and your Pi (and SD card) will appreciate it. The advice about checking...
by JohnsUPS
Wed Feb 26, 2020 11:30 am
Forum: Beginners
Topic: Non Contact Voltage Detector Mashup
Replies: 11
Views: 731

Re: Non Contact Voltage Detector Mashup

JohnUPS Thank you. If I read the datasheet correctly the Vertis unit switch threshold is 15amp. I contacted both companies for a product that will trigger at 1amp. Guppy, Not sure what model you were looking at......they have many to choose from with various features. I actually tested the unit tha...
by JohnsUPS
Wed Feb 26, 2020 11:16 am
Forum: Beginners
Topic: Please help me understand the clock pin of Serial RS232 communication
Replies: 27
Views: 1097

Re: Please help me understand the clock pin of Serial RS232 communication

I did exactly this a while back using cheap Chinese calipers. During my research into the protocol, I came across the Mitutoyo information, and also having a Mitutoyo caliper, I was interested in decoding it too. However their serial protocol is much different, so I opted to skip. Because you alread...
by JohnsUPS
Tue Feb 25, 2020 12:26 pm
Forum: Beginners
Topic: Non Contact Voltage Detector Mashup
Replies: 11
Views: 731

Re: Non Contact Voltage Detector Mashup

All that you need is a current sensing switch - something like this: https://www.nktechnologies.com/current-sensing-switches/asm-current-sensing-switch/ or this: https://www.veris.com/Category/Current-spcMonitoring/Current-spcSwitch/Fixed-spcTrip.aspx These are basically current transformers with bu...
by JohnsUPS
Tue Feb 18, 2020 11:03 pm
Forum: Automation, sensing and robotics
Topic: Acs712 current sensor
Replies: 6
Views: 369

Re: Acs712 current sensor

If that is all you need to do, then there are multiple other ways to do this. The simplest would be to use a light-dependent resistor/photoresistor. When light hits the LDR, the resistance decreases. Depending on your ambient light situation, minor additional circuitry might be needed. Also, you cou...
by JohnsUPS
Tue Feb 18, 2020 2:43 pm
Forum: Other
Topic: Physical Button to Switch OS - - Help
Replies: 2
Views: 841

Re: Physical Button to Switch OS - - Help

Not only would using two Pis provide redundancy, but the switchover could be made to be almost instant, versus waiting for the other OS to come up.....
by JohnsUPS
Tue Feb 18, 2020 2:27 pm
Forum: Automation, sensing and robotics
Topic: Acs712 current sensor
Replies: 6
Views: 369

Re: Acs712 current sensor

The ACS712 sensor has an analog output, therefore, you will need to also use an analog-to-digital converter. The A-D will have a digital output that you can then send to the Pi. There are many A-D converters out there that can be used. How much accuracy do you need? That will dictate the bit resolut...
by JohnsUPS
Thu Feb 06, 2020 3:27 pm
Forum: Off topic discussion
Topic: Best example of a bad forum post?
Replies: 87
Views: 8064

Re: Best example of a bad forum post?

At risk of going further off topic here, but I suspect the problem is deeper than that. There appears to be a tendancy for folk to not take resposibility or action for themselves instead expecting others to do the work for them. Across the board not just in tech areas. Yeah, this is one of my peeve...
by JohnsUPS
Thu Feb 06, 2020 3:08 am
Forum: Off topic discussion
Topic: Best example of a bad forum post?
Replies: 87
Views: 8064

Re: Best example of a bad forum post?

I prefer to give the person posting the benefit of the doubt regardless of how they pose their question(s). Everyone has different backgrounds and levels of expertise and also command of English. Although most of the people that frequent this forum are technically oriented (and many are very sharp) ...
by JohnsUPS
Thu Feb 06, 2020 2:39 am
Forum: Automation, sensing and robotics
Topic: Current Transformer Current/Voltage monitoring
Replies: 1
Views: 571

Re: Current Transformer Current/Voltage monitoring

Usually the mechanism to monitor power (I am saying power because you're wanting to monitor both current and voltage) is to begin as you have done, with current transformers. You will also need potential transformers. A set of each will be needed for each phase. There are certainly other solutions, ...
by JohnsUPS
Fri Jan 31, 2020 12:10 am
Forum: Advanced users
Topic: How best to log 12 volt lead acid battery voltage with a Raspberry Pi?
Replies: 6
Views: 1290

Re: How best to log 12 volt lead acid battery voltage with a Raspberry Pi?

I think the simplest solution would be using an integrated voltage/current/power monitoring chip such as INA226 . You can get breakout boards from the usual sources, just check that the shunt resistor is suitable for your maximum current. Code examples for reading the chip on a RPi: https://github....
by JohnsUPS
Thu Jan 30, 2020 11:48 pm
Forum: General discussion
Topic: Distance Sensors
Replies: 8
Views: 1054

Re: Distance Sensors

This surely is a difficult measurement problem, given the various densities of the materials and temperature. Because it was said that absolute accuracy isn't needed, I thought I'd throw this out there for the OP's consideration: How viable would measuring the outside temperature gradient of the tan...

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