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by Mark_T
Wed Nov 04, 2015 12:38 pm
Forum: Beginners
Topic: Sleep Mode - and or turn off backlight?
Replies: 202
Views: 96499

Re: Sleep Mode - and or turn off backlight?

I suspect the limitation on brightness support is an EMI issue?
by Mark_T
Wed Nov 04, 2015 12:28 pm
Forum: Official Foundation Display
Topic: The screen is 'sliding' ( gap between screen and bezel )
Replies: 31
Views: 12815

Re: The screen is 'sliding' ( gap between screen and bezel )

The cause of the touchscreen part coming off is the Pimoroni acrylic case pushing it off by a mm or so, and the glue is actually viscoelastic and eventually gives up. If you add washers under the acrylic for the mounting screws it no longer exerts a force on the touchscreen layer which should preven...
by Mark_T
Tue Oct 06, 2015 6:02 pm
Forum: Official Foundation Display
Topic: Touch sensitivity and speed
Replies: 2
Views: 1046

Re: Touch sensitivity and speed

You can't get zero latency, its a question of how much latency you can tolerate. The capacitive touch IC will be doing some processing, sending it on to the RPi, then that has to be translated into cursor position and style decisions, then that gets painted on a frame buffer, then that framebuffer i...
by Mark_T
Tue Oct 06, 2015 5:55 pm
Forum: Official Foundation Display
Topic: Display auto backlight off
Replies: 3
Views: 1064

Re: Display auto backlight off

Other posts in this forum indicate that this is a feature being actively developed, but isn't released yet,
many are eagerly awaiting it.
by Mark_T
Sun Apr 19, 2015 8:19 pm
Forum: Automation, sensing and robotics
Topic: Current, Voltage, Power Factor sensor
Replies: 8
Views: 3458

Re: Current, Voltage, Power Factor sensor

Power factor is nothing to do with lead/lag angles, that only works for pure sinusoids (the mains is not pure these days), the power factor is the ratio mean power ------------------ Vrms x Irms This definition both works for any waveform and explains how to calculate it: Average the values VI, V^2 ...
by Mark_T
Sun Apr 19, 2015 8:09 pm
Forum: Automation, sensing and robotics
Topic: We want to build a quadcopter.
Replies: 12
Views: 4433

Re: We want to build a quadcopter.

For that money you're forced to use small coreless DC motors and make a miniature copter, which will save a lot of money for motors/ESCs and battery, but then you're forced to use small lightweight controller board (not a RaspPi)... Make up a rough BOM and cost it out, you'll see what I mean - the f...
by Mark_T
Fri Apr 10, 2015 2:43 pm
Forum: Camera board
Topic: raspberry pi always restart
Replies: 3
Views: 1019

Re: raspberry pi always restart

To be more exact, inadequate power - the supply might be OK and the cable poor, for instance,
note that USB data cables are not suitable for the power jack, a two-wire power-only lead
is recommended.

Well, that's the most likely explanation given the facts.
by Mark_T
Tue Apr 07, 2015 12:09 pm
Forum: Automation, sensing and robotics
Topic: home automation
Replies: 8
Views: 2975

Re: home automation

You can get commercial remotely controlled light and power switches using ISM band(s), these would be another approach (which the advantage of complete isolation from the mains). Hacking into the remote control might be a bit kludgey, but there is information out there on the over-the-air protocol f...
by Mark_T
Tue Apr 07, 2015 12:05 pm
Forum: Automation, sensing and robotics
Topic: DMX
Replies: 5
Views: 1251

Re: DMX

Are you asking about using a Pi as a DMX512 receiver (as opposed to controller?)
by Mark_T
Tue Apr 07, 2015 12:03 pm
Forum: Automation, sensing and robotics
Topic: CNC Dremel
Replies: 6
Views: 2461

Re: CNC Dremel

1mm/second is extremely slow, even for threaded rod, since a good stepper + driver should get you to 1000rpm or beyond. You have to use low impedance bipolar steppers driven from chopper driver circuit and 24V or more supply. Most CNC motion systems use acme threaded lead-screws or ball-screw lead-s...
by Mark_T
Wed Mar 25, 2015 2:32 pm
Forum: Camera board
Topic: Bizzare defect with my RPi Camera
Replies: 16
Views: 3502

Re: Bizzare defect with my RPi Camera

Let me repeat, this is definitely a lack of IR filter, nothing to do with white balance.

Somehow a regular Pi Camera module has been made without the IR filter.

Note the original images the black socks become white. White balance doesn't
affect black objects!
by Mark_T
Mon Mar 23, 2015 1:01 pm
Forum: Automation, sensing and robotics
Topic: Controlling a 2kW heat plate
Replies: 10
Views: 2523

Re: Controlling a 2kW heat plate

Water can easily reach > 100C - often happens in a microwave oven for example, then suddenly the cup/bowl undergoes rapid boiling, throwing the hot water out. This is called superheating. Its less likely to happen with ordinary stoves as the heat from below causes dissolved air to bubble out from th...
by Mark_T
Mon Mar 23, 2015 12:18 pm
Forum: Beginners
Topic: Making files executable
Replies: 10
Views: 13047

Re: Making files executable

There's nothing special about chmod, you always need to name a file correctly to refer to it, so if its not in the current directory you'll have to give a relative or absolute path, or else cd to the relevant directory. If you want to see the permissions of files use "ls -l" ls -l Desktop/VNC.sh The...
by Mark_T
Sun Mar 22, 2015 4:35 pm
Forum: Camera board
Topic: Ultraviolet light with NOIR camera
Replies: 17
Views: 11142

Re: Ultraviolet light with NOIR camera

Firstly UV covers a whole wide patch of the spectrum, so its key to know which wavelength is important. It may be hard UV (the fact glass absorbs 100% suggests this). http://randombio.com/glass-spectra.png You can buy optical filters to any specification you like, but typically expensive. The PiCam ...
by Mark_T
Sun Mar 22, 2015 4:22 pm
Forum: Camera board
Topic: Bizzare defect with my RPi Camera
Replies: 16
Views: 3502

Re: Bizzare defect with my RPi Camera

Your device _definitely_ lacks an IR filter - so its a PiNOIr sensor on a regular board,
a manufacturing error at a guess.

No amount of white-balance error could make a black settee white! Most black fabric is
very pale in near IR.
by Mark_T
Sun Mar 22, 2015 4:17 pm
Forum: Automation, sensing and robotics
Topic: home robot for cleaning, like roomba
Replies: 4
Views: 1880

Re: home robot for cleaning, like roomba

Perhaps look out for secondhand (perhaps broken/damaged) Roombas? Probably cheap and you can replace
as much of it as you like to adapt to your needs. I'm sure the internet wil throw-up examples of mods to the
basic machine.
by Mark_T
Sun Mar 22, 2015 4:14 pm
Forum: Automation, sensing and robotics
Topic: Current and Voltage sensors, what are the options?
Replies: 7
Views: 4111

Re: Current and Voltage sensors, what are the options?

Many multimeters have an opto-isolated USB serial interface
which can be used for data-logging - just get two of these?
by Mark_T
Thu Mar 19, 2015 9:19 pm
Forum: Automation, sensing and robotics
Topic: Step motor + board non-responsive
Replies: 4
Views: 856

Re: Step motor + board non-responsive

If in3 isn't working that would be enough to stop it turning. All 4 inputs should be cycling correctly,
and in a valid sequence.
by Mark_T
Mon Mar 16, 2015 3:12 pm
Forum: Automation, sensing and robotics
Topic: Brushless motor speed control - RPi
Replies: 1
Views: 726

Re: Brushless motor speed control - RPi

ESCs don't work like that out of the box, they expect to be controlled from a RC receiver with
mid-range (ie 90 degrees) to be idle level (roughly). Each ESC has its own default
response curve and many can have this reprogrammed.
by Mark_T
Mon Mar 16, 2015 3:00 pm
Forum: Beginners
Topic: upgrading pi b+ to pi 2: ok to just swap card?
Replies: 21
Views: 2083

Re: upgrading pi b+ to pi 2: ok to just swap card?

I've never had success burning a NOOBs card on linux, and there's no point as
dd'ing raspbian (or whatever) is perfectly reliable. I can see that it might be
convenient on a more opaque OS, but its basically a workaround for a problem
that doesn't exist on Linux.
by Mark_T
Mon Mar 16, 2015 2:57 pm
Forum: Beginners
Topic: High Amp Motors with the Pi
Replies: 18
Views: 10065

Re: High Amp Motors with the Pi

Diode: STTH6012W placed across source/drain of mosfet Capacitor: combination 100nF, 10uF and 10,000uF across power supply. NO! The diode goes across the motor. It provides a path for the current in the motor windings when the MOSFET switches off. All power MOSFETs already have a built-in diode as p...
by Mark_T
Thu Mar 12, 2015 1:53 am
Forum: Beginners
Topic: High Amp Motors with the Pi
Replies: 18
Views: 10065

Re: High Amp Motors with the Pi

85A stall current probably means about 10A at nominal load, and if your supply is current limited you can reduce the maximum current the motor controller has to deal with. With careful ramping up of PWM and current monitoring (always wise to have current monitoring), you could keep the working curre...
by Mark_T
Tue Mar 10, 2015 10:16 pm
Forum: Beginners
Topic: OS for B+ model
Replies: 4
Views: 604

Re: OS for B+ model

The latest versions will run on any Pi, older versions will not. If you fully update a raspbian on the B+ to
the latest version if should then boot on a Pi 2 - I think there's a FAQ entry about this when the
Pi 2 was released.
by Mark_T
Tue Mar 10, 2015 10:09 pm
Forum: Automation, sensing and robotics
Topic: opencv-simple blob detector issue
Replies: 6
Views: 3060

Re: opencv-simple blob detector issue

All I'm asking is that you provide some information about what you are trying to
do - people genuinely cannot read minds, and it makes it much easier to help
if given details (in particular links and code).

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