Raspberry Pi Forums

PiGraham

Adafruit just links to bitmit.net [deliberate non-link there] The problem is Bitmit redirects that randomly - sometimes to "bestsellers", sometimes to "hot auctions" etc.. My guess is that there may be adult content in "hot auctions" at some times of the day there are certainly explicit advert list...

PiGraham

I see no ads at all on the Adafruit page.

PiGraham

https://tylerjones.me/wp-content/uploads//2012/11/npn-arduino-rpi-buffer.jpg The left circuit will only drive 3.3 to the Arduino, since as the emitter rises to 3.3 the B-E junction is no longer forward biased and the C-E path turns off. It's safe and should work, since 3.3 will, I think, exceed the...

PiGraham

What short circuit currents?? If the input turns on the transistor and the Pi turn on the gpio as output low then there is a short from 3.3, through your transistor, into the gpio pin and to ground via the Pio output gate. Not a problem if it can be guaranteed that the gpio is never configured as o...

PiGraham

Can someone confirm if any of the GPIO lines are guaranteed to reset to a specific state (input?) and stay there throughout booting of any official Raspbian release?

PiGraham

Something that can touch the bottom in shallows is at risk of catching or tangling. non-contact is a safer option. It seems there are fish finder sonar devices for >~£20. E.g. this one Feature: 1. Detect and display grass, short & tall weeds, sand, and rocks on seabed 2. Get the approximate location...

PiGraham

You can't depend upon the state of the gpios during Pi initialisation. Even if a solution appears to work now it might be broken in a subsequent firmware/kernel release. Is that really true? If so it has some serious implications for many Pi applications.A defined reset state is usually rather impo...

PiGraham

simplesi wrote:I set my inputs to be have internal pull-ups resistors - e.g. in Python GPIO.setup(22,GPIO.IN,pull_up_down=GPIO.PUD_UP)

What happens before your Python code executes? Switchable pull-ups may not be there all the time.

PiGraham

This is a fun idea. It's a watery outdoor Roomba!

Sonar seems a good choice for sensor since you mainly want to avoid banks and shallows.
Maybe you could interface to a fish finder gadget.

PiGraham

Good to see some signs of interest.

I was just reading about how to make Jam!
http://raspberryjam.org.uk/make-a-raspberryjam/

http://www.raspberrypi.org/phpBB3/viewt ... 57&t=10615

PiGraham

As Joan says, the Pi only has digital interfaces on board. This sensor outputs 0.3V to 3V so you could use it as a fixed distance sensor that would change a digital input 0 - 1 at some distance 10cm - 80cm. The alternatives is to use a ADC add on and read the analogue voltage. Perhaps something like...

PiGraham

Hmm, yes that's possible. But, if I understand what you're suggesting, I think I will loose the ability to set temperatures at will over the internet, because the other thermostat will have precedence over the Pi one way or the other (temps too high, OR temps too low). I already have a thermostat i...

PiGraham

I owe you an apology. I now see that you have used additional components to modify the operation of the 555 to do edge re-triggering.

Carry on!

PiGraham

[quote="techpaul"]Actually be dubious about wikipedia look at the datasheet and the modified circuit, the level at which it triggers is 1/3 Vcc and CANNOT be retriggered within its timeout period (and a bit). Look at modification input goes low to trigger, and the charge cap is shorted when the inpu...

PiGraham

OK, just a couple of comments on "Failsafe use of GPIO pin". More or less in-line with your idea: 1. Monitor the state of whatever the output is supposed to switch via a GPIO input and test in your application to check that the device is on when it's supposed to be and off otherwise. 2. You can use ...

PiGraham

I don't know.

PiGraham

I take that back it appears they might be produced at Sony which is what I have been assuming but not sure. http://www.youtube.com/watch?v=sLfE-wGZJqk&feature=player_embedded I have been checking Farnell - element 14 website https://export.farnell.com/jsp/raspi/orderPad.jsp?&country=GB for few week...

PiGraham

If this is a teaching assignment it make sense. It's a simple two-axis CNC. Electronic cams are often use in place of mechanical cams (especially where elaborate or variable cam profiles are required).

PiGraham

That's sound advice James. A cam or a crank are anothe ways to translate rotation into linear motion, so that would work for direct drive or stepper/servo drive. I can't think of many functional reasons to use a motor driven system. You could vary the cross-sectional profile of the coil (why?) You c...

PiGraham

Search "leadscrew". Turn a threaded rod with a stepper motor, or DC motor + encoder, and it will control the position of a "nut" on the rod. You can literally use a length of studding (threaded metal rod) and a nut (as in nut and bolt) for a light-duty system. For something more serious you might us...

PiGraham

I would agree that in general multiple systems and multiple UPS for real failsafe. In this case as this is one HVAC system, which will have inbuilt modes that put the unit safe when power fails (no doubt always off), powering one or more Pis from the same mains feed as the HVAC is adequate as neith...

PiGraham

Graham, how would you do it then? I have searched around somewhat but could not find any other practical solutions. If you have a better method, or know of one, can you share that with us? According to the number of times some of the diagrams in this post have been looked at, there seems to be a lo...

PiGraham

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.

PiGraham

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...

PiGraham

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...

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