Buying stuff

• There is always something to buy. If you know you need something that is actually good. It is worse not knowing something useful exists. A curious case is when the the thing in a photo is not named: "crocodile clip" was a word that alluded me, until I browsed some shop's website —possibly Pimoroni— much like a child circling items in an Argos catalogue before Christmas.
• PiHut and Pimoroni are the official distributors of Pis. All other shops (e.g. Amazon and eBay) resell them at a higher price. However, many components can be bought for cheaper off eBay, especially as a multi-buy. Other microcontroller boards may have a similar situation: I wanted an STM32 Nucleo because unlike other Arduino alternatives it has a cool cyan on white colour scheme and RS components was the correct seller.
• Always get or make a case even if it costs more than the damn board, accidents happen, full stop.
• The official Pi 4 case looks oh-so sleek but cannot accomodate a fan and majorly does not have a flap for GPIO cables. Compare with the official Pi zero case which does.

• Heat tarnished audio jack

  eBay is full of folk selling unused Pis. A Pi Zero costs £10+3 (you can only buy one at the time), but a larger pi has the advantage of multiple USB, no shims, no squeezing, ethernet etc. So it is rather a convenience thing than a cost thing —although a lot seem kit purchases of a Pi in a case with fans.
  (1) the audio jack gets tarnishes after prolonged Pi usage, so a shiny audio jack means an unused Pi —so zero chance the PMC is fried
  (2) a Pi 2 does not have WiFi but goes for £10-15 (auctions)
  (3) a Pi 3 goes for £20-25 depending on the extras

Management

The RAM size simply tippex on

I have wasted so much time trying to remember what is what because I did not start off with a system... even a paper notebook would have helped.

• add in each microSD cards a file describing what it is
• Set up a jupyter notebook and slack notification on boot: details of common tasks here. 
• post-it notes come off, sharpies don't.
• decide where to keep your code or you have to relearn what you did. And always save a copy of your history just in case.
• Sending 5V to 3.3V will fry the PMC. The power out of the pins will be low. It is not worth desoldering and resoldering a new one. Add simple Tippex on the chip to mark it —as opposed to testing it each time one is in doubt. A nicer solution are white paint extra-fine pens.
• Tupperware boxes are great for storing components
• Print several pages of the GPIO pins ...and use a pencil: like a DnD character sheet it will be a mess, but mighty handy.

Soldering

From left to right: a 18 gauge stranded wire shoved in, two 22 gauge wires crimped into header pin connectors, two commercial wires (for the fan)

GPIO pins and sensors

• A sensor bundle mega kit is not worth the money. They are the cheapest sensors and as soon as you start a project you will upgrade to an ever so slightly more expensive sensor. A good example is the temperature sensor DHT11, which is nowhere as good as the £5 BME280. Another example is the cheap 433.92 MHz receiver, which has a 5 m range. Like all components, multi-buy of the same item is cheaper on eBay.
• Breadboards are really handy. A T-cobbler seems handy but isn't really.
• For a pi zero, the coluor-coded header pins are a must.
• Mark the GND pins with a black Sharpie
• Essentials: misc. resistors, misc. LEDs, MCP3008
• Non-essential: rectifiers, shrink wrap tubing and capacitors (maybe with the exception of 10 nF ceramic caps)
• The MCP3008 is a pain to set up. Testing it is set up correctly is essential using a 3.3V pin.
• In Python Adafruit ditalio is definitely better than the RPi.GPIO module. Even if a lot of code online uses the latter, it is always handy to convert to the latter, which is cleaner and can be use with a context manager.
• Graphite is conductive, so mechanical pencil leads make excellent rust-proof rods for things like water level
• Cheap thin water tubing for irrigation is a bad investment as it's not flexible and prone to flick off the connectors.
• HATs? Adafruit &co. want to sell you stuff and often what is needed is a dirt cheap component.

Pi camera

• The official Pi camera (V2) costs £25 and is 8 MP. However, off eBay or Amazon you can buy for £10 or less as combinations a V1.3 5 MP camera. Who cares for the difference in resolution if the rate limiting part is the focus?
• The ribbon of a Pi can easily damage: it is cheaper to buy a new 5 MP camera with different cables included.
• The lens focal length of a pi camera can be altered with a pair of tweezers, however, there is a lens adjustment tool for the V2 camera that makes life easier.
• Online there are some lenses available that are M12 lenses, which is 12 mm in diameter for which a standard M12 mount works on a pi camera. However, there are lots of clip on lenses for smart phones online, which need some tinkering as the lens sticks out, unlike a phone. The ring within the clip from the lens kit is a "lens lock", but the diameter is odd (2/3", 1.67 mm, possibly D mount?), so I've been unable to find a lens lock to space it out. Duck tape, plasticard and bluetack is a bad route. The distance between the lens and the sensor is called flange length: on clip-on lenses this is very small (lock ring height), so, proportionally, being off by a few millimeters ruins the photo, so sticking with M12 lenses is a better solution (or maybe the High Quality pi camera which has a CS mount already...).
• Further on the above, many 3-in-1 lenses come with a macro that screws off a wideangle lens. This is actually is a M12 to C adaptor. Theoretically, one could go M12 to C to Nikon F-mount or Sony E-mount and use a DSLR lens... but in that case one really ought to be using the £50 high definition pi camera  or even better controlling a DSLR camera directly with a pi via gphoto2 (sudo apt-get install python3-gphoto2 and bob is your uncle).
• In low light, when a LED ring is not an option stacking multiple photos, scaling and histogram stretching the image is good strategy.

Other

Lure of 64bit

PoE