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by PiGraham
Wed Sep 05, 2018 12:47 pm
Forum: General discussion
Topic: How to dispose of broken lipo
Replies: 40
Views: 1301

Re: How to dispose of broken lipo

Isn't there a risk of setting fire to the lithium in a broken cell by immersing it in water? Yes, I believe that's true. Which is why most disposal guides say don't do that if damaged; don't immerse in water, don't attempt to discharge. The guide quoted above doesn't say that though, which surprise...
by PiGraham
Wed Sep 05, 2018 12:44 pm
Forum: General discussion
Topic: How to dispose of broken lipo
Replies: 40
Views: 1301

Re: How to dispose of broken lipo

So the best thing is to ensure it has no energy left to do any damage before disposing of it. Stab it with a fork ,drive nails through it. Be sure to do this somewhere that won't burn and protect yourself. When it has burned down think about where to dispose of the remains. Just yesterday Microsoft...
by PiGraham
Wed Sep 05, 2018 12:31 pm
Forum: General discussion
Topic: How to dispose of broken lipo
Replies: 40
Views: 1301

Re: How to dispose of broken lipo

The salt water thing is curious. I suppose it's intended to gently discharge the cells without relying on the inter-cell connections. I believe you are right. I recall the salt is needed to make the water more conductive than it otherwise would be. It is effectively creating 'a higher resistance wr...
by PiGraham
Wed Sep 05, 2018 11:28 am
Forum: General discussion
Topic: How to dispose of broken lipo
Replies: 40
Views: 1301

Re: How to dispose of broken lipo

The salt water thing is curious. I suppose it's intended to gently discharge the cells without relying on the inter-cell connections.
But lithum metal combusts in water so be careful with damaged cells. I'd prefer to discharge the battery dry but I have no expertise in this.

https://binged.it/2oJQHHk
by PiGraham
Wed Sep 05, 2018 11:19 am
Forum: General discussion
Topic: How to dispose of broken lipo
Replies: 40
Views: 1301

Re: How to dispose of broken lipo

From Joans's link: For safety reasons, it’s best that LiPo cells be fully discharged before disposal (however, if physically damaged it is NOT recommended to discharge LiPo cells before disposal - see below for details). The batteries must also be cool before proceeding with disposal instructions. 1...
by PiGraham
Wed Sep 05, 2018 10:28 am
Forum: General discussion
Topic: How to dispose of broken lipo
Replies: 40
Views: 1301

Re: How to dispose of broken lipo

There is a risk of fire with LiPo so I would pick it up with tongs or slide it onto a ceramic plate of something like that so I could get it outside without touching it or getting too close to it. Then I would leave it on a non-flammable surface (e.g. concrete path or paving slab) in the open and aw...
by PiGraham
Mon Sep 03, 2018 3:36 pm
Forum: General discussion
Topic: Smallest wired keyboard
Replies: 17
Views: 3627

Re: Smallest wired keyboard

I was curious. I found this info on using with Arduino on serial.
http://cliffle.com/project/chatpad/arduino/
Apologies if this is duplicating info already posted.

A USB to serial adaptor (potentially built into a USB cable) could make an easy way to connect it.
by PiGraham
Sun Sep 02, 2018 5:39 pm
Forum: Automation, sensing and robotics
Topic: House Alarm - very remote PIR to trigger 12v Lights
Replies: 8
Views: 558

Re: House Alarm - very remote PIR to trigger 12v Lights

If you have WiFi coverage you could use a WiFi controlled mains socket.
https://www.amazon.co.uk/ANEKEN-Assista ... kets&psc=1

Probably the cheapest and safest option.
by PiGraham
Fri Aug 31, 2018 2:33 pm
Forum: Other projects
Topic: Transferring photos taken on one pi onto another pi
Replies: 7
Views: 483

Re: Transferring photos taken on one pi onto another pi

With NFS or SSHFS you can mount the remote system's file system on the RPi that's capturing the photo and the transfer is completely automagical. No intervention needed. Whether that uses NFS or SSHFS (FTP or Samba/CIFS having already been rejected) is arbitrary. Mounting something remote is the mo...
by PiGraham
Fri Aug 31, 2018 8:29 am
Forum: Other projects
Topic: Transferring photos taken on one pi onto another pi
Replies: 7
Views: 483

Re: Transferring photos taken on one pi onto another pi

Why not sshfs? It's already enabled. This isn't about why not to use 'X'. There are plenty of options. The key point was you can easily have one Pi save photos directly to the storage on another Pi (or other device). Plus you can save locally and automatically have that storage synchronise with sto...
by PiGraham
Thu Aug 30, 2018 1:41 pm
Forum: Other projects
Topic: Transferring photos taken on one pi onto another pi
Replies: 7
Views: 483

Re: Transferring photos taken on one pi onto another pi

Or, assuming these are on the same home network, use a network shared folder (NFS, Samba etc) or FTP. Cloud storage is another option.
by PiGraham
Thu Aug 30, 2018 10:14 am
Forum: Automation, sensing and robotics
Topic: Swimming lap counter
Replies: 8
Views: 2554

Re: Swimming lap counter

It looks like things like fitbit can track swim lengths. You might be able to use an accelerometer to get a crude estimate of position or direction. Integrating acceleration gives velocity and integrating velocity gives you position. That its basically adding values. It's usually noisy data and the ...
by PiGraham
Wed Aug 29, 2018 7:18 pm
Forum: Networking and servers
Topic: Why do I get a high ping when I plug in a second network cable?
Replies: 3
Views: 207

Re: Why do I get a high ping when I plug in a second network cable?

Finally figured it out. Seems like some kind of power issue. As soon as I unplug other USB devices the ping is normal again. When I plug them in again it rises immediately. Dunno why it just depends on the cable being connected and not the USB ethernet adapter itself. Just a thought The on-board Et...
by PiGraham
Wed Aug 29, 2018 10:53 am
Forum: Advanced users
Topic: Compare two images then convert the new image into text
Replies: 18
Views: 812

Re: Compare two images then convert the new image into text

So basically, I'm going to make a handheld device that can check any Scrabble board and use it to tally points of players and a dictionary to check each words. If you want this to be handheld and portable it might make more sense to do it as a smartphone App because that gives you a neat handheld d...
by PiGraham
Wed Aug 29, 2018 10:48 am
Forum: Advanced users
Topic: Compare two images then convert the new image into text
Replies: 18
Views: 812

Re: Compare two images then convert the new image into text

I suggest you use pattern matching to locate distinctive features on the face of the Scrabble board. That means you can avoid confusions with scenes that may contains grids but are not Scrabble boards. This may not be as simple as it sounds since there seem to be a vast range of designs for Scrabble...
by PiGraham
Tue Aug 28, 2018 7:54 pm
Forum: Python
Topic: pigpio callbacks
Replies: 16
Views: 798

Re: pigpio callbacks

You have the step count when you build the wave. A wave of ten cycles will move the motor ten steps. Why add callbacks and extra counters? Alternatively, just looping ten times to turn a gpio on, sleep, off, sleep, moves the motor ten steps. You can do that with pigpio or any other GPIO library. You...
by PiGraham
Tue Aug 28, 2018 6:26 pm
Forum: Python
Topic: pigpio callbacks
Replies: 16
Views: 798

Re: pigpio callbacks

You may want to do cleverer things to move faster or accelerate the longer the button is held but the above covers the basics.
by PiGraham
Tue Aug 28, 2018 6:24 pm
Forum: Python
Topic: pigpio callbacks
Replies: 16
Views: 798

Re: pigpio callbacks

The information about homing sounds good, thanks. You can then provide pulses to move the motor and you just have to keep track of how many pulses you send to the driver, which is a quantity managed in your code so you don't need to count it from gpio pin callbacks. This is the part I'm confused ab...
by PiGraham
Tue Aug 28, 2018 5:34 pm
Forum: Python
Topic: pigpio callbacks
Replies: 16
Views: 798

Re: pigpio callbacks

I'm just learning as I go, so I'd welcome any suggestions. What do you think is the best way to accomplish the goal of allowing a user to infinitely position a nut along a motor-driven lead screw where they want with a button press to start motion and another button to stop motion? A stepper motor ...
by PiGraham
Tue Aug 28, 2018 3:17 pm
Forum: Advanced users
Topic: Compare two images then convert the new image into text
Replies: 18
Views: 812

Re: Compare two images then convert the new image into text

It still might help if you were to describe what your purpose is in developing the app that you are working on: e.g. are you hoping to have a Scrabble-playing app that can respond to an opponent who is using a real Scrabble board? YES! Absolutely this. Why don't people explain their purposes when t...
by PiGraham
Tue Aug 28, 2018 3:15 pm
Forum: Advanced users
Topic: Compare two images then convert the new image into text
Replies: 18
Views: 812

Re: Compare two images then convert the new image into text

If this is literally a crossword grid or Scrabble board with one character in each box you may have to do something custom. You could use an edge detection filter then a Hough Transform to find the lines of the grid then extract the contents of each box (region of interest ROI) and pass that through...
by PiGraham
Tue Aug 28, 2018 3:03 pm
Forum: Python
Topic: pigpio callbacks
Replies: 16
Views: 798

Re: pigpio callbacks

moderatelyfunky wrote:
Tue Aug 28, 2018 2:56 pm
@PiGraham, I'm using polulu drv8825 drivers with some generic bipolar steppers
OK, so why do think it necessary to count edges of a PWM signal?
Why are you using PWM if you want to control position?
by PiGraham
Tue Aug 28, 2018 2:48 pm
Forum: Advanced users
Topic: Compare two images then convert the new image into text
Replies: 18
Views: 812

Re: Compare two images then convert the new image into text

Best to OCR the two images of the board to get characters into two arrays then compare the character arrays to find the differences.
by PiGraham
Tue Aug 28, 2018 2:31 pm
Forum: Python
Topic: pigpio callbacks
Replies: 16
Views: 798

Re: pigpio callbacks

You can use PWM for speed control with typical DC motors, but you don't get "steps" of position. Movement is continuous and you need some sort of position sensor to measure and thus control position. You can use RC servos with PWM to control position but then the position should be what you request ...
by PiGraham
Tue Aug 28, 2018 8:42 am
Forum: General discussion
Topic: Count clock ticks on a pin (gpio)
Replies: 3
Views: 247

Re: Count clock ticks on a pin (gpio)

I don't think that will work. Frequency is too high and implied timing resolution in microseconds is too small for high level language callbacks in a userland Linux system. Why don't you divide the clock on the MCU and output a slower clock to the Pi? Or you could use the Pi to generate a more accur...

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