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--- guides:raspberrypi [2013/02/19 08:58] – daveake
+++ guides:raspberrypi [2014/11/03 20:56] (current) – realflash
@@ Line 6: / Line 6: @@
 	* It's a bit large and heavy compared to most Arduinos
 	* It has an SD card poking out of the end (delicate)
-	* It runs Linux which is not a real-time operating system
+	* It will take some effort and Linux knowledge to run a real-time kernel on it
 	* Unlike the Arduino you don't have a large selection of shields to choose from
@@ Line 47: / Line 47: @@
 The Pi has various onboard voltages fed from regulators.  The only one we're interested in is the 3.3V line because that's handy for running the GPS etc.  However there's only supposed to be 50mA spare from this line, so you will probably be better off supplying 3.3V from your own regulator.  If you do this, consider using a switching regulator to supply the GPS etc and the pi (remove the onboard regulator and insert your 3.3V on the GPIO connector).  There's an article on the internet about this.
+Unless you're using USB devices, you DO NOT need to supply 5V to the Pi - thee whole thing will run happily from 3.3V and an external regulator.  To do this, remove the existing 3.3V regulator (or just snip off the 2 legs) and apply 3.3V tot he 3.3V AND 5V lines from your regulator.  Your two options then are to use a real LDO (the PI one is rubbish and has a 1.12V dropout) such as the MCP1825S, then run that from 4 Lithium cells.  Second option is to use a switching regulator and more cells (the switchers tend to have a higher dropout).  Either way, calculate your expected run time and then test it.
@@ Line 58: / Line 60: @@
 ===== Radio =====
-Linux isn't a real time operating system, and therefore does not provide accurate timing that you can use in a tracker application to generate rtty.  If you have a beard and sandals you may scoff at this challenge, muttering about "kernel drivers" and "timer interrupts".  If so, have fun.  For the rest of us, it's possible to cheat and use the serial port to send rtty directly to an NTX2 radio transmitter.  You'll need a series resistor to set the frequency gap, and bias resistors to set the voltage offset, just as you would when using a single pin on an Arduino.
+Linux isn't a real time operating system, and therefore does not provide accurate timing that you can use in a tracker application to generate rtty.  If you have a beard and sandals you may scoff at this challenge, muttering about "kernel drivers" and "timer interrupts".  If so, head to the [[guides:raspberrypi_advanced|Advanced]] page and have fun.  For the rest of us, it's possible to cheat and use the serial port to send rtty directly to an NTX2 radio transmitter.  You'll need a series resistor to set the frequency gap, and bias resistors to set the voltage offset, just as you would when using a single pin on an Arduino.
 You're now probably wondering how to connect the pi to a GPS now that we've used the serial port for the radio.  The pi does have more than one serial port however (as far as can tell) you can only map one at a time to the GPIO connector.  So without some hardware hackery we only have one port available.  My solution was to share that port between NTX2 and GPS.  i.e. Tx goes to the NTX2 and Rx to the GPS.  This means the GPS cannot be "talked to" so I used a Lassen which needs no initialisation.  You could use a UBlox, but you'd then need to connect Tx to the NTX2 and GPS, meaning that those initialisation strings will go out over the air too.  Not a big problem really.
 Another option would be to connect to the GPS using a different serial connection - i2c or SPI.  If you use i2c with a UBlox receiver you'll find it doesn't work, because the UBlox does "clock stretching" at arbitrary times, and the Pi ii2c driver doesn't handle that.  You may have to resort, as I did, to using a software "bit-banging" i2c implementation.
+Another option would be to use a PL2303 (USB To Serial) device. It's cheap (1€) and quite light. This is working great to discuss with the radio (NTX2) or with the GPS (Ublox). It has been used successfully for UGGY payload with 150 bauds for the radio. For the Ublox that have 3.3V logic, check if your PL2303 is 3.3V or 5V logic and adjust if needed (in case you still power the Pi with 5V). There is a Pin of the chip to unplug from the 5V, and plug to the 3.3V to change the serial logic.
 Typically we run the radio at 50 baud.  This is possible on the pi but when I tried it it worked for a few characters only.  I've had better results with 300, 600 and 1200 baud.  The Lassen GPS runs at 4800 baud and the UBlox at 9600 and neither can be reprogrammed down to low speeds, so this means that the tracker program needs to switch baud rates to read the GPS, then switch before transmitting.  And then back again.  So this all imposes some down-time between transmissions.
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 	* Make sure the serial port isn't doing NL --> CRNL conversion or similar (otherwise your binary image data is going to get messed up).
+** Update **
+For those using the PiCAM and Python there is a python module giving access to the camera rather than having to use os.system. This provides a cleaner interface and will potentially be much faster.
+Write up on raspberrypi.org can be found at [[http://www.raspberrypi.org/archives/5672]] with installation details at the bottom of the page.
+The project details are available on [[https://pypi.python.org/pypi/picamera/|PYPI]] and [[https://github.com/waveform80/picamera/|GitHub]]. The module is also installable via ''apt-get install python-picamera'' or ''apt-get install python3-picamera''
+**Update - NEW RASPBERRY PI ADD-ON BOARD**
+If this all sounds a bit too much work, you can use Dave & Anthony's [[http://www.pi-in-the-sky.com/|PITS]] add-on board for the Raspberry Pi!