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by PiGraham
Fri May 25, 2018 8:51 pm
Forum: Automation, sensing and robotics
Topic: Sensing 50Hz frequency deviation fast
Replies: 12
Views: 257

Re: Sensing 50Hz frequency deviation fast

hippy wrote:
Fri May 25, 2018 2:05 pm
PiGraham wrote:
Fri May 25, 2018 12:58 pm
For certain you cannot do this with just a Raspberry Pi
I am not entirely convinced that is the case.
I just mean you can't wire a Pi to mains and not fry everything. Some other circuitry is required, such as a zero crossing detecto opto-isolator
by PiGraham
Fri May 25, 2018 1:47 pm
Forum: Beginners
Topic: Help.. PI 3 to control motors from sense hat (self levelling)
Replies: 13
Views: 278

Re: Help.. PI 3 to control motors from sense hat (self levelling)

JFI - you don't use corner jacks to level a caravan https://www.practicalcaravan.com/forum/general/46360-levelling-up The info from Swift caravans was interesting. The gist seems to be that the main weight is taken on the wheels and the "steadies" hold the chassis steady around the axel fulcrum. I ...
by PiGraham
Fri May 25, 2018 12:58 pm
Forum: Automation, sensing and robotics
Topic: Sensing 50Hz frequency deviation fast
Replies: 12
Views: 257

Re: Sensing 50Hz frequency deviation fast

For certain you cannot do this with just a Raspberry Pi so saying a Pi is all you have and you can't use anything else doesn't make sense. A Pi running Ultiboo can do some pretty real-time things. It's worth a look. You should try to quantify your timing requirements in more detail. What happens if ...
by PiGraham
Thu May 24, 2018 7:02 pm
Forum: Add-ons
Topic: Outlier Temperature readings
Replies: 2
Views: 75

Re: Outlier Temperature readings

Take a rolling median of multiple readings. Keep a list of, say, 20 readings. Append the new reading at the head and remove the oldest reading at the tail then sort the list by value and take the middle value (index 10) and use that as the temperature for your alarm. I expect there is a median funct...
by PiGraham
Thu May 24, 2018 12:40 pm
Forum: Beginners
Topic: Help.. PI 3 to control motors from sense hat (self levelling)
Replies: 13
Views: 278

Re: Help.. PI 3 to control motors from sense hat (self levelling)

You would need to select motors that can apply enough torque to turn the jacks. You could gauge that using a torque wrench. Maybe something like this http://www.sears.com/craftsman-3-8-in-dr-beam-style-torque-wrench/p-00932999000P Then you need to decide how quickly you need the output shaft to turn...
by PiGraham
Thu May 24, 2018 8:06 am
Forum: Automation, sensing and robotics
Topic: Controlling a 360 degree servo
Replies: 4
Views: 183

Re: Controlling a 360 degree servo

You control speed, not position, with the PWM signal. If you need position control you will have to your own positional feedback and control loop.
As mattmiller says you stop movement by setting PWM to middle of the range.
by PiGraham
Tue May 22, 2018 8:51 am
Forum: C/C++
Topic: Increase GPIO toggle frequency
Replies: 24
Views: 656

Re: Increase GPIO toggle frequency

Hrater,
Thanks for those posts. They are very useful.
by PiGraham
Sun May 20, 2018 7:18 am
Forum: C/C++
Topic: Increase GPIO toggle frequency
Replies: 24
Views: 656

Re: Increase GPIO toggle frequency

If I were to look at using hardware SPI instead, how would that work given that these devices don't have a CS pin? Would I manually pull down one of the RPi CS pins, write the data (using the existing MOSI and CLK channels), and then pull the 'fake' CS pin HIGH? I'd really like to avoid hardware SP...
by PiGraham
Sun May 20, 2018 6:31 am
Forum: C/C++
Topic: Increase GPIO toggle frequency
Replies: 24
Views: 656

Re: Increase GPIO toggle frequency

That's a very fair point. I will have numerous other SPI devices in use in the very near future, and would prefer to keep these drivers separate if at all possible. Another consideration is the fact that I'll be moving to a non-RPi Linux device in the near future as well, the SPI details of which I...
by PiGraham
Wed May 16, 2018 8:14 am
Forum: Automation, sensing and robotics
Topic: monitoring rotary encoder on fast motor with pigpio - improving performance?
Replies: 14
Views: 382

Re: monitoring rotary encoder on fast motor with pigpio - improving performance?

My take is finding ways of doing things on the Pi without having to resort to additional hardware is a win win situation. The person doing the development learns a lot and it lowers the entry cost for everyone else wanting to experiment in the area - they may not need to spend money and time buying...
by PiGraham
Tue May 15, 2018 8:15 pm
Forum: Beginners
Topic: LED Strip colouring in reverse with PiGPIO
Replies: 18
Views: 418

Re: LED Strip colouring in reverse with PiGPIO

Yeah, you're right - it's not a MOSFET! It's a regulator, and the bottom line says -3.3, so it's a 3v3 version That makes for a novel power switch! I suppose that raising the ref pin to 3.3V turns the regulator off and dropping the voltage to zero puts it into normal regulator mode with shorted out...
by PiGraham
Tue May 15, 2018 6:43 pm
Forum: Automation, sensing and robotics
Topic: monitoring rotary encoder on fast motor with pigpio - improving performance?
Replies: 14
Views: 382

Re: monitoring rotary encoder on fast motor with pigpio - improving performance?

Yu are pushing the limits of what's practical under Linux. You could offload the counting to hardware. There ate quadrature counter ics that can cope with high rate encoder counting. Your coide could then just query the position when it needs it using i2c. Pushing? Yes, reached? No. So why add more...
by PiGraham
Tue May 15, 2018 6:37 pm
Forum: Gaming
Topic: Exagear and Games
Replies: 9
Views: 388

Re: Exagear and Games

I have a Raspberry Pi 3 B+ which I am using as my desktop computer. I am planning on purchasing Exagear. However, I wish to legally purchase games for Exagear. Does anyone have any suggestions? I find it difficult to find information. Isn't the point of exagear to run PC x86 software on other platf...
by PiGraham
Tue May 15, 2018 6:33 pm
Forum: Advanced users
Topic: Mean of 60 temperature sensors
Replies: 17
Views: 699

Re: Mean of 60 temperature sensors

As scruss points out it's the cabling that is the catch to this situation. The OP says it's a large area commercial building with three stories and 50 to 60 sensors per story for a total of 150 to 180 sensors. This could be many miles of wires through a potentially very noisy environment and having...
by PiGraham
Tue May 15, 2018 9:43 am
Forum: Automation, sensing and robotics
Topic: monitoring rotary encoder on fast motor with pigpio - improving performance?
Replies: 14
Views: 382

Re: monitoring rotary encoder on fast motor with pigpio - improving performance?

You can use pigpio from c which should hep a bit. Yu are pushing the limits of what's practical under Linux. You could offload the counting to hardware. There ate quadrature counter ics that can cope with high rate encoder counting. Your coide could then just query the position when it needs it usin...
by PiGraham
Fri May 11, 2018 10:45 am
Forum: General discussion
Topic: E ink as Monitor for raspbian Lite
Replies: 4
Views: 216

Re: E ink as Monitor for raspbian Lite

i was hoping to just use the bash terminal. But does the refresh rate suggest you can't see what you typing for a second? I was looking at this display here http://www.ebay.co.uk/itm/like/123098315023?clk_rvr_id=1526739387782&vectorid=229508&lgeo=1&item=123098315023&rmvSB=true. But i can much docum...
by PiGraham
Fri May 11, 2018 10:29 am
Forum: General discussion
Topic: Model train project help
Replies: 13
Views: 556

Re: Model train project help

Options that I would consider are; PyGame https://www.pygame.org/news A python library for creating multimedia applications. It has functions to draw lines, or more complex widgets on screen. Tkinter - Pre-installed with most python distributions. A slightly old fashioned but powerful GUI framework...
by PiGraham
Thu May 10, 2018 7:45 am
Forum: Troubleshooting
Topic: Pi still has some power after removing power cable
Replies: 8
Views: 271

Re: Pi still has some power after removing power cable

There is a 5V feed on HDMI isn't there? On later Pi (except Zeroes) a self-powered high-side FET (AP2331W,RT9741CGV) is used to steer the Pi 5V to HDMI H5V. My underestanding is that should prevent back-feeding from the TV to the Pi. Curious. The HDMI seems to be the only possible source of power i...
by PiGraham
Thu May 10, 2018 7:36 am
Forum: General discussion
Topic: Flame Sensor
Replies: 11
Views: 341

Re: Flame Sensor

Since the DO os open collector it make no difference to that signal what voltage is connected to Vcc on the module. I suggest using the specified 5V. Use a pullup to 3.3V either using the built-in pullup or an external resistor. According to the sensor schematic "D0" has an internal pullup (R2 - 10...
by PiGraham
Thu May 10, 2018 7:22 am
Forum: Raspbian
Topic: Display file "real time" like in a console?
Replies: 9
Views: 310

Re: Display file "real time" like in a console?

Code: Select all

tail -f mylogfile 
For details on following a file that is changing see:

Code: Select all

man tail
by PiGraham
Wed May 09, 2018 5:19 pm
Forum: Troubleshooting
Topic: Pi still has some power after removing power cable
Replies: 8
Views: 271

Re: Pi still has some power after removing power cable

There is a 5V feed on HDMI isn't there? This looks relevant if not a simple answer: https://www.raspberrypi.org/forums/viewtopic.php?t=2518#p32811 There is the MHL standard which is intended to supply charging power whilst being a HDMI sink, so a TV would supply power to a device plugged into it. Al...
by PiGraham
Wed May 09, 2018 4:50 pm
Forum: General discussion
Topic: Flame Sensor
Replies: 11
Views: 341

Re: Flame Sensor

Thus the flame sensor "Vcc" must be connected to 3.3 V on the RPi rather than 5 V as in the Arduino example. This keeps the output "D0" in the proper voltage range for RPi, that is 0 V and 3.3 V. Since the DO os open collector it make no difference to that signal what voltage is connected to Vcc on...
by PiGraham
Wed May 09, 2018 4:09 pm
Forum: General discussion
Topic: Flame Sensor
Replies: 11
Views: 341

Re: Flame Sensor

It should be OK to use with RPi According to the circuit posted by MArkTF the output DO is drivern by an LM393 comparator and the TI datasheet for that says this about the output: The output of the LM193 series is the uncommitted collector of a grounded-emitter NPN output transistor. Many collectors...
by PiGraham
Wed May 09, 2018 1:55 pm
Forum: General discussion
Topic: Flame Sensor
Replies: 11
Views: 341

Re: Flame Sensor

If you want help using a sensor or other device you need to tell people what it is that you have (or intend to get). A link to a product page or data sheet is usually most useful.
by PiGraham
Wed May 09, 2018 11:32 am
Forum: Python
Topic: Help a fool aka building a selfie box for a wedding
Replies: 3
Views: 125

Re: Help a fool aka building a selfie box for a wedding

The search term "photobooth" may help you. I suggest that taking the photos is much more important than printing them on the spot so get the photo taking working first and embellish later if you have time. You could get by without a GUI. Some lights and a button and a preview display would do as a m...

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