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by JohnsUPS
Wed May 06, 2020 8:21 pm
Forum: Other projects
Topic: Struggling to understand voltage drop
Replies: 8
Views: 350

Re: Struggling to understand voltage drop

The circuit appears like it should work, but what I am suspecting is that the coil of your relay is loading down your power source (the source isn't able to supply the necessary current), and as a result, the voltage is dropping. How big is this relay (what is the coil voltage/coil current rating?) ...
by JohnsUPS
Wed May 06, 2020 8:09 pm
Forum: Beginners
Topic: Need help measuring the speed of a small ball
Replies: 10
Views: 706

Re: Need help measuring the speed of a small ball

Ahhhh....reminds me of times past - played my share of foos back in the day..... If I get what you are describing correctly, you basically just want to measure the speed of the ball during a penalty kick or such as the ball enters the goal. Because the ball won't loose any significant amount of spee...
by JohnsUPS
Mon Apr 20, 2020 2:54 pm
Forum: Beginners
Topic: Lathe tachometer
Replies: 4
Views: 193

Re: Lathe tachometer

I did something similar to that. The object of the project was to flash a strobe light at a given time in the rotation to "freeze" the motion of the stock. This was designed for a wood lathe, however it would work on a metal lathe too. There was an adjustable timer delay between the sensor and the s...
by JohnsUPS
Mon Apr 13, 2020 8:58 pm
Forum: HATs and other add-ons
Topic: prototyping board w/o strips ?
Replies: 5
Views: 310

Re: prototyping board w/o strips ?

For making one off projects and prototyping, using the 0.1" on center, 0.040" dia plated through hole boards with point-to-point wiring, does the trick for me. The wire is usually 26 ga Kynar insulated wire wrapping wire that is stripped, formed and soldered as necessary to make connections. I never...
by JohnsUPS
Fri Apr 10, 2020 7:51 pm
Forum: General discussion
Topic: Raspberry Pi 3 with light sensor and LED!
Replies: 4
Views: 202

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: 224

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: 289

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: 8
Views: 358

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: 585

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: 1138

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: 227

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: 11
Views: 440

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: 458

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: 182

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: 965

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: 410

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: 522

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: 904

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: 529

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: 802

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: 529

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: 280

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: 667

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.....

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