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by drgeoff
Tue Feb 13, 2018 9:34 pm
Forum: Beginners
Topic: MCP3008 use for detecting battery capacity
Replies: 6
Views: 188

Re: MCP3008 use for detecting battery capacity

You can measure any higher voltage than the input range of an ADC by resistively dividing the high voltage. If necessary (in your case it isn't strictly needed) you can apply a scaling factor (multiplier) to whatever number comes out of the ADC chip in the subsequent digital domain. https://learn.sp...
by drgeoff
Tue Feb 13, 2018 11:55 am
Forum: Off topic discussion
Topic: It *has* to happen!
Replies: 28
Views: 1116

Re: It *has* to happen!

So if you buy 5000 Pi0s, you have a greater than 50% chance that at least two of them have the same MAC address? Yes, that is what probability theory says if the MAC addresses are assigned randomly from the entire pool of 2^24 possibles, ie with no regard for ones that have already been used. 2^24 ...
by drgeoff
Tue Feb 13, 2018 10:57 am
Forum: Off topic discussion
Topic: It *has* to happen!
Replies: 28
Views: 1116

Re: It *has* to happen!

I think it is 4824 before you have > 50% chance of having 2 with the same address if you have n RPis the number of possible pairs is n(n-1)/2. Each pair has a probability of 1 in 2^24 of having the same MAC. So for a 50% probability of one pair with both MACs the same you need (2^24)/2 pairs Puttin...
by drgeoff
Mon Feb 12, 2018 10:49 pm
Forum: Off topic discussion
Topic: It *has* to happen!
Replies: 28
Views: 1116

Re: It *has* to happen!

if you have 2 RPis the chance of both having the same MAC is 1 in 16777216. I'm not sure that's correct because my understanding is that addresses are chosen at random, that not all 16777216 combinations will have been used before some of those are reused. Like a 16777216 sided dice rolled every ti...
by drgeoff
Mon Feb 12, 2018 9:37 pm
Forum: Off topic discussion
Topic: It *has* to happen!
Replies: 28
Views: 1116

Re: It *has* to happen!

my maths is not up to it but it is like the birthday problem https://en.wikipedia.org/wiki/Birthday_problem as the PI has 24bit [16777216) possible vaules then the chances of having 2 pi's with the the same IP when that >50% is ... well I leave that to someone who knows what they are calculating ;)...
by drgeoff
Sun Feb 11, 2018 10:51 pm
Forum: Advanced users
Topic: Raspberry Image comparison - fog detection
Replies: 7
Views: 317

Re: Raspberry Image comparison - fog detection

fabio_m wrote:
Sun Feb 11, 2018 9:56 pm
About the Sobel instead I'm still not sure on how to get a simple "number" from all of that.
I've already told you how to get a single number after the edge detector.
by drgeoff
Sun Feb 11, 2018 10:22 pm
Forum: Troubleshooting
Topic: ACT LED intensity
Replies: 19
Views: 456

Re: ACT LED intensity

You have been given enough hints.

Do some reading up on PWM in general (not RPi specific) and when you understand it, the penny should drop. If it does not, perhaps you should consider changing faculty. :(
by drgeoff
Sun Feb 11, 2018 9:56 pm
Forum: Troubleshooting
Topic: ACT LED intensity
Replies: 19
Views: 456

Re: ACT LED intensity

Yes a Pulse-Width Modulation which you can control the brightness of an LED which is connected using GPIO pins on an external board You already said you can turn the ACT LED on and off. Either you don't understand the principles of PWM or you are very slow at putting two and two together. i do unde...
by drgeoff
Sun Feb 11, 2018 9:47 pm
Forum: Troubleshooting
Topic: ACT LED intensity
Replies: 19
Views: 456

Re: ACT LED intensity

Ever heard of PWM? Yes a Pulse-Width Modulation which you can control the brightness of an LED which is connected using GPIO pins on an external board You already said you can turn the ACT LED on and off. Either you don't understand the principles of PWM or you are very slow at putting two and two ...
by drgeoff
Sun Feb 11, 2018 9:42 pm
Forum: Beginners
Topic: Data acquisition with Rapsberry PI in Industrial Environment
Replies: 5
Views: 231

Re: Data acquisition with Rapsberry PI in Industrial Environment

I see nothing in what CarliosEdward wrote about a RPi controlling (directly or indirectly) any machine so boyoh's concerns are largely irrelevant. RPis have no analogue inputs so cannot be directly connected to analogue sensors. The interfacing circuits will probably need to be custom designed for e...
by drgeoff
Sun Feb 11, 2018 9:27 pm
Forum: Troubleshooting
Topic: ACT LED intensity
Replies: 19
Views: 456

Re: ACT LED intensity

Ever heard of PWM?
by drgeoff
Sun Feb 11, 2018 9:11 pm
Forum: Troubleshooting
Topic: ACT LED intensity
Replies: 19
Views: 456

Re: ACT LED intensity

If you have been set an assignment that is beyond you, you should seek advice from those who are there to teach you. That is the only way they realise that their methods are not having the required outcomes. Thanks for the answer but it did not help Apart from asking here, what have you done and ho...
by drgeoff
Sun Feb 11, 2018 7:49 pm
Forum: Troubleshooting
Topic: ACT LED intensity
Replies: 19
Views: 456

Re: ACT LED intensity

If you have been set an assignment that is beyond you, you should seek advice from those who are there to teach you. That is the only way they realise that their methods are not having the required outcomes.
by drgeoff
Sun Feb 11, 2018 4:23 pm
Forum: Beginners
Topic: My Q is easy: how to set static IP?
Replies: 7
Views: 243

Re: My Q is easy: how to set static IP?

you need to be careful when setting static IP addresses so an not to set them to low in the address range that you router DHCP might also try to use them. Not all routers use the lower addresses for the DHCP pool. For example, the majority of ISP supplied xDSL modem-routers in the UK default to 192...
by drgeoff
Sun Feb 11, 2018 7:51 am
Forum: Beginners
Topic: Confused about LED Resistor choice???
Replies: 5
Views: 225

Re: Confused about LED Resistor choice???

Your method of calculating the resistor value for a current of 20 mA is correct. However a look at the spec sheet for the LED at https://www.superbrightleds.com/moreinfo/through-hole/5mm-blue-led-15-degree-viewing-angle-5500-mcd/269/ indicates that 20 mA is the maximun current it should be operated ...
by drgeoff
Sat Feb 10, 2018 10:45 pm
Forum: Beginners
Topic: Creating an image
Replies: 1
Views: 108

Re: Creating an image

Put the card in a USB card reader and mount it in a machine* running Linux and use gparted to reduce the partition size. Then use dd to make an image large enough to include the partitions.

(* possibly your RPi running Raspbian from another card.)
by drgeoff
Sat Feb 10, 2018 10:32 pm
Forum: Beginners
Topic: Using the RasPi as a Parallel Terminal
Replies: 11
Views: 523

Re: Using the RasPi as a Parallel Terminal

The 46505 was a clone of the Motorola 6845 CRT controller (https://en.wikipedia.org/wiki/Motorola_6845). Get the info on that. Typically used with a simple mapping of memory address to raster scan.
by drgeoff
Sat Feb 10, 2018 10:25 pm
Forum: Beginners
Topic: Using a Pi Zero W to detect a mains powered doorbell press
Replies: 8
Views: 407

Re: Using a Pi Zero W to detect a mains powered doorbell press

It works! I've posted a description of the setup and provided the code I used. Thanks for your help, D BoyOh I'm a bit sceptic al of the use of the 0.1u f capacitor to cancel RF interference out. I think the problem is the DC from the bridge rectifier not being smoothed, this is causing a 100hz 0 t...
by drgeoff
Sat Feb 10, 2018 2:29 pm
Forum: Beginners
Topic: PiCamera right next to (magnetic) speaker?
Replies: 2
Views: 115

Re: PiCamera right next to (magnetic) speaker?

Unless you are talking about a pop concert speaker with tens of amps through it I wouldn't envisage any EMF issues. But obviously wise to use a twisted pair of wires to the speaker and keep them away from the camera ribbon.
by drgeoff
Fri Feb 09, 2018 9:49 pm
Forum: Beginners
Topic: Using a Pi Zero W to detect a mains powered doorbell press
Replies: 8
Views: 407

Re: Using a Pi Zero W to detect a mains powered doorbell press

Might I suggest a smoothing capacitor on the DC side of the bridge rectifier with out this you will get a 100hz UK 120hz USA wave form, @boyoh What harm, mis-operation or any other bad thing will occur without a smoothing capacitor in the use case under discussion?
by drgeoff
Fri Feb 09, 2018 5:19 pm
Forum: Troubleshooting
Topic: Setting a static IP on stretch??
Replies: 9
Views: 412

Re: Setting a static IP on stretch??

Current /etc/network/interfaces: # interfaces(5) file used by ifup(8) and ifdown(8) # Please note that this file is written to be used with dhcpcd # For static IP, consult /etc/dhcpcd.conf and 'man dhcpcd.conf' # Include files from /etc/network/interfaces.d: source-directory /etc/network/interfaces...
by drgeoff
Fri Feb 09, 2018 3:22 pm
Forum: Advanced users
Topic: Raspberry Image comparison - fog detection
Replies: 7
Views: 317

Re: Raspberry Image comparison - fog detection

Just two untested ideas. 1. Compare the standard deviation of pixel values from fog and no-fog images. Are they significantly different? Probably not necessary to use all the pixels. 2. Run an edge detector over the images. Sum the absolute values. Significant difference between fog and no fog?
by drgeoff
Wed Feb 07, 2018 3:21 pm
Forum: Beginners
Topic: 16 gb raspberry card prepration
Replies: 29
Views: 997

Re: 16 gb raspberry card prepration

Hi All, If its a fake or damaged card then why is it proper;y working on ubuntu laptop and able to partition/read/write files etc ?? I feel in the beckground some matching code or something is lying due to which its only not able to boot..what u say ?? Without testing something reaching a conclusio...
by drgeoff
Wed Feb 07, 2018 3:19 pm
Forum: Beginners
Topic: 16 gb raspberry card prepration
Replies: 29
Views: 997

Re: 16 gb raspberry card prepration

Hi All, If its a fake or damaged card then why is it proper;y working on ubuntu laptop and able to partition/read/write files etc ?? I feel in the beckground some matching code or something is lying due to which its only not able to boot..what u say ?? Without testing something reaching a conclusio...
by drgeoff
Wed Feb 07, 2018 1:11 pm
Forum: Beginners
Topic: 16 gb raspberry card prepration
Replies: 29
Views: 997

Re: 16 gb raspberry card prepration

I am using same card and card reader for reading and writing files with partitioning perfectly and when I am using other card on same rpi board the board in properly booting even, i am able perform all operation properly. There is some other factor is lying which we are not able to catch..pls help ...

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