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by PiGraham
Tue Jun 18, 2013 9:23 pm
Forum: Automation, sensing and robotics
Topic: Failsafe(r) use of GPIO pin driving critical applications
Replies: 41
Views: 12495

Re: Failsafe use of GPIO pin driving critical applications

Hey, no problem. I wouldn't do it that way but it's your design and your property. Do what gives you peace of mind.
by PiGraham
Tue Jun 18, 2013 4:42 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Output VGA video directly from Pi
Replies: 22
Views: 28004

Re: Output VGA video directly from Pi

I also like the idea of bitbanging a display output. It takes me back to the ZX80/80/Spectrum era! ( One of the original "Raspberry Pi" concept cheap home computers when I was 11! ) Pixel clock for 640x480 VGA is 25MHz. I think the SPI port will clock at 32MHz. Maybe some monitors would tolerate tha...
by PiGraham
Tue Jun 18, 2013 1:52 pm
Forum: Automation, sensing and robotics
Topic: Failsafe(r) use of GPIO pin driving critical applications
Replies: 41
Views: 12495

Re: Failsafe use of GPIO pin driving critical applications

I'm not sure you gain anything in reliability by putting another circuit in series. What are the relative probabilities of the various failure modes? How reliable is your 555 circuit (it could fail)? Is the additional probability of failure due to the 555 circuit outweighed by the probability of the...
by PiGraham
Tue Jun 18, 2013 12:14 pm
Forum: For sale
Topic: 1.8" TFT LCD Shield board v2
Replies: 101
Views: 39154

Re: 1.8" TFT LCD Shield board v2

What are the specs on this display, resolution and frame rate in particular. What frame rate is possible when displaying video preview from PiCam? What are thesizes and mounting hole dimensions? Power consumption may be important to some. Is it compatible with PiFace or GertBoard? WIll it run alongs...
by PiGraham
Tue Jun 18, 2013 11:24 am
Forum: Camera board
Topic: My Quadcopter with Raspberry Pi Camera
Replies: 37
Views: 21912

Re: My Quadcopter with Raspberry Pi Camera

I just finished my new Quadcopter and on the first flight I tested the Raspberry Pi Camera (1080p @ 30fps) vs my old 808 keychain cam. ( Sorry for the shaky video! The quad is not "PID tuned" yet. (My first flight with this quad). ) http://youtu.be/-dReyGvzAQw :) Can't wait to get the quad PID tune...
by PiGraham
Tue Jun 18, 2013 8:41 am
Forum: Staffroom, classroom and projects
Topic: Stealth Nighthawk F-117A TVDongle
Replies: 14
Views: 5129

Re: Stealth Nighthawk F-117A TVDongle

My argument is that Android is not a suitable OS for the target market of the RaspPi. It might be suitable for the XBMC crowd, and it might have a place in schools, but it is deficient as a child's own PC because it needs to be programmed externally. Not so, there are various programming tools that...
by PiGraham
Tue Jun 18, 2013 7:46 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: 0-10v PWM possible?
Replies: 36
Views: 11180

Re: 0-10v PWM possible?

Yes, indeed, if you have a 10V source then using a simple level shifter would be simple. The level shifter can consist of a NPN transistor that shorts a 4K7 pullup-to-10V to GND. You control it with the PWM GPIO signal using a 2K2 resistor between the GPIO and the base of the transistor. Do note th...
by PiGraham
Tue Jun 18, 2013 6:53 am
Forum: Staffroom, classroom and projects
Topic: Stealth Nighthawk F-117A TVDongle
Replies: 14
Views: 5129

Re: Stealth Nighthawk F-117A TVDongle

Android is programmable. Android TV sticks, and Android phones and tablets are another way to realise the RasPi goals. Can you program Android, in Darvic and native code, on Android? I'm enough of a programmer to know it has to be theoretically possible, but I've not seen it done -- only Forth and ...
by PiGraham
Tue Jun 18, 2013 6:07 am
Forum: Staffroom, classroom and projects
Topic: Stealth Nighthawk F-117A TVDongle
Replies: 14
Views: 5129

Re: Stealth Nighthawk F-117A TVDongle

... It is compatible with Pi software, apparently. Here's a video of it running Raspbian: http://youtu.be/Q28mX7dWbeU Looks cool but I think I'd rather support the Pi foundation by getting a real Raspberry Pi. Interesting. Is that a stock Raspi image? The GUI looks slow. You can see the screen pain...
by PiGraham
Sun Jun 16, 2013 9:28 am
Forum: Staffroom, classroom and projects
Topic: Stealth Nighthawk F-117A TVDongle
Replies: 14
Views: 5129

Re: Stealth Nighthawk F-117A TVDongle

There are lots of devices like that, most with better hardware specs. Google "android tv stick". They will run other flavours of linux too. That's true, but there aren't any devices with the Raspberry Pi CPU and GPU yet. OK, but this F-117A isn't identical hardware to a Pi, is it? Can you take a Ra...
by PiGraham
Sun Jun 16, 2013 8:16 am
Forum: Staffroom, classroom and projects
Topic: Stealth Nighthawk F-117A TVDongle
Replies: 14
Views: 5129

Re: Stealth Nighthawk F-117A TVDongle

There are lots of devices like that, most with better hardware specs. Google "android tv stick". They will run other flavours of linux too.
by PiGraham
Sat Jun 15, 2013 5:29 pm
Forum: Automation, sensing and robotics
Topic: Raspi with DFRobot Dual Motor Controller
Replies: 9
Views: 3037

Re: @Gbaman

Ok thanks, i hooked up pin six to the board and it worked like a charm :D . I was wondering though, since my robot goes 10 mp/h on True/1, and comes to a dead stop on False/0, would be able to use PWM to control the speed of my motors? Thanks for the help! -Cudy Yes. Look up pigpio. The author, Joa...
by PiGraham
Sat Jun 15, 2013 10:28 am
Forum: Troubleshooting
Topic: piface again and again
Replies: 12
Views: 1683

Re: piface again and again

I followed instructions on the Piface development blog "Installing the software yourself in Raspbian" and installed on current Raspbian and it worked for me. Model B Rev 2. Pi.
by PiGraham
Sat Jun 15, 2013 10:09 am
Forum: Automation, sensing and robotics
Topic: Failsafe(r) use of GPIO pin driving critical applications
Replies: 41
Views: 12495

Re: Failsafe use of GPIO pin driving critical applications

I don't think we need to use airplane type redundancy and fail safe systems for an HVAC system. I do not want to downplay anything said, but if it's that critical, I would not use a Pi (or two or three) in the first place. This is very true. Of course any safety critical system should not be implem...
by PiGraham
Sat Jun 15, 2013 9:46 am
Forum: User groups and events
Topic: Portsmouth Jam 27th July?
Replies: 37
Views: 12219

Re: Portsmouth Jam 27th July?

Is anyone here interested in a Portsmouth Jam?
by PiGraham
Fri Jun 14, 2013 5:22 pm
Forum: Graphics, sound and multimedia
Topic: LCD Scrolling text - internet radio
Replies: 54
Views: 26409

Re: LCD Scrolling text - internet radio

The simple way is to scroll a bit then check buttons and repeat. Button polling only waits for one increment of scolling, and scrolling pauses while you handle a button event. A more serious method is to have one program thread do scrolling and another handle the button input. This can get complex a...
by PiGraham
Fri Jun 14, 2013 4:04 pm
Forum: General discussion
Topic: Pi Video capture
Replies: 4
Views: 2540

Re: Pi Video capture

There is no mention of TV2 support in Linux here:
http://www.hauppauge.com/pages/faq/supp ... linux.html
or here:
http://www.linuxtv.org/wiki/index.php/Hauppauge
so it doesn't look promising.
by PiGraham
Fri Jun 14, 2013 2:36 pm
Forum: Automation, sensing and robotics
Topic: PWM for servos, motors, and LEDs plus plus
Replies: 71
Views: 42548

Re: PWM for servos, motors, and LEDs plus plus

It's meant to be a safety feature. The library locks a file when it starts to ensure only one copy is running at a time. The file should be deleted when the library terminates. Just delete the file, e.g. rm /var/run/pigpiod.pid Presumably turning off the Pi with the library active will leave a lock...
by PiGraham
Fri Jun 14, 2013 12:15 pm
Forum: User groups and events
Topic: Portsmouth Jam 27th July?
Replies: 37
Views: 12219

Re: Portsmouth Jam 27th July?

I'm in the area and interested in getting involved.
by PiGraham
Fri Jun 14, 2013 8:48 am
Forum: Automation, sensing and robotics
Topic: Home automation
Replies: 13
Views: 6692

Re: Home automation

I haven't tried this, but the documentation says you can send a byte array: write(data) Parameters: data – Data to send. Returns: Number of bytes written. Raises SerialTimeoutException: In case a write timeout is configured for the port and the time is exceeded. Write the string data to the port. Ch...
by PiGraham
Thu Jun 13, 2013 2:56 pm
Forum: Bare metal, Assembly language
Topic: GPIO Pin to LED
Replies: 4
Views: 2641

Re: GPIO Pin to LED

You only need LED and resistor. You can generally assume an LED will drop 2V. The GPIO can drive max 16mA. If you play safe and design for 10mA your resistor should drop 1.2V @ 10mA R = 1.2/0.01 = 120R If the resistor value is too high you won't see the LED light. If it's too low you may blow your P...
by PiGraham
Thu Jun 13, 2013 2:46 pm
Forum: Automation, sensing and robotics
Topic: Question about using raspberry pi to drive two servos, laser
Replies: 9
Views: 4098

Re: Question about using raspberry pi to drive two servos, l

According to the specifications for your laser module: 2.8 - 5.2V DC voltage input 25mA max current draw You can run it from 3.3V, but any one GPIO pin can supply a max of 16mA ( see here ), so you could not drive the laser at full power from a GPIO. If your servo control outputs don't draw too much...
by PiGraham
Thu Jun 13, 2013 12:13 pm
Forum: General discussion
Topic: Wiring a shift register
Replies: 8
Views: 2147

Re: Wiring a shift register

I don't think that chip is a good choice. It's inputs are 5V logic. Look at the table "Static electrical characteristics" and you will find that "Input high voltage" is 3.6V minimum, so the Pi's 3.3v logic won't turn on the inputs to this chip. The output sinks 2.6mA ("Output low (sink) current") so...

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