Electronics next project

I’m suffering from analysis paralysis as I ponder what electronic project to do next to level up (to both level up my skills and my equipment). This is related to the microcontroller inventory and the nonshopping list. Here are some 58 projects I could try to do, mostly in random order with five randomly chosen but with a few manually chosen to move to the top list of finalists:

• house thermometer (indoor, outdoor, logging)
• Joule Thief as a simple battery tester if nothing else
• 7-segment display with 7 scavenged discrete LEDs in some kind of case with slits and partitions, which can be very large
• use a speaker as a microphone to get bidirectional audio on a microcontroller.
• make the strip of giant LEDs shine so we can illuminate with it
• audio amp driving one or more of the speakers here
• metronome with relays
• low-bandwidth 433MHz license-free SDR for kilometer-scale robust communication
• pulse soldering: a circuit to deliver a calibrated amount of energy at a calibrated power level for, for example, battery pack construction or hair-wire soldering
• ultra-low-power FM radio transmitter to listen to music wirelessly
• display text on a 7-segment LED screen from an AVR or STM32
• timer with relay to turn off the water pump after 20'
• plant waterer to keep the plants from dying; this probably involves a microwave oven relay, a washing machine valve, a microcontroller, and some transistors

• hot air pencil: thermostatic control of air temperature permits rapid localized heating, very useful for rework and electronics scavenging, as well as preheat for soldering
• ultrasound measurement with two piezos and some oil, to see what frequencies I can get through the oil; this might require the Blue Pill
• basic Magic Kazoo: you hum into a microphone on one end, and it does pitch ID and synthesizes a musical instrument out the other
• lightbulb thermometer using a lightbulb as the temperature sensor
• read the digital caliper’s output port to get another 20-micron-precision positional feedback source
• stepper controller: drive a low-power stepper motor with some transistors and a microcontroller
• an electromagnet, pure and simple
• electrolysis controller to permit precise control of electroplating, electro-etching, and similar processes
• copper-wire foam cutter (see Copper Segelin)
• micro-engraver with three piezos, or two piezos and electro-etching, or one piezo and several electrodes, as a testbed for micro-engraving ideas
• stainless steel wool foam cutter: it’s about 0.2Ω per 100mm, which is in the same ballpark as thinner copper wire for the copper segelín, but instead of burning at 300° it can get to over 800°, which is plenty for cutting styrofoam.
• adjustable switching power supply using discontinuous conduction mode to get current limiting
• program the PALs I scavenged to compute some particular logic function
• noise-based optical position encoder: by measuring randomly varying transmissivity or reflectivity along a linear track, it can rapidly determine its precise position
• read and write SD card from AVR or STM32: SD cards support SPI, and this enables a lot of projects that otherwise need way too much space.
• air conditioner remote control to control the air conditioner with infrared
• FM radio receiver to listen to the radio
• Blue Pill oscilloscope, only up to a megahertz or two but still better than a sound card
• ultrasonic vector image transmission (see audio vector image)
• program my ATMega328s with the Duemilanove, the ones that are in a tube
• program the ATTiny2313s I have a tube full of here so I can use them for things like capacitance measurement
• humidity sensor (see PET dielectric spectroscopy)
• make an MPPT to measure a red LED in the sun to find out how much energy you can harvest from it and at what power level
• recognize whistling with an AVR to command household electronics
• synthesize voice with AVR and speaker to get output
• program the ATTiny45s so I can use them for things like my notebook
• dielectric spectroscopy: identify materials, especially including humidity, capacitively through their frequency-dependent permittivity
• program Blink onto one of the Blue Pills so I can start using them
• test the PAL delay line I scavenged from a VCR
• Lissajous projector, scanning a laser pointer with a resonating nutating mirror. Once the mirror has a stable resonance set up, maybe from a speaker, you can tune in a picture by moving a photodiode into the illuminated area to find the overall period, then to corners and across the center to find the phase
• impedance tomography sensor to detect touches on a resistive surface with just a few electrodes and a microcontroller
• emulate a PS/2 keyboard to get data from microcontrollers onto bigger computers (see machine-readable microcontroller output)
• build a simple circuit with hair wire to see if it can be made feasible
• data reception with bidirectional LEDs as extensively tested for, among other things, PJON
• linear motor with aluminum sheet consisting of two or three coils that can levitate and move the sheet; this probably requires some pretty hefty power
• thermostat-controlled microfurnace for things like firing pottery
• current microbalance to weigh light things by counteracting their weight with a precisely measured electromagnetic force
• adjustable linear power supply hanging off an ATX or power-brick power supply so I have an adjustable voltage; this becomes a lot more useful once it has some kind of readout, and ideally current limiting too; if it depends on the upstream power supply for voltage regulation it can be just a trimpot and an emitter follower
• TransistorTester, maybe not a super sophisticated one
• rotational capacitive sensor made of paper towel tubes and aluminum foil to measure rotational position with some precision, thus providing feedback for DC motors
• capacitor meter: with Duemilanove, to begin with
• test PS/2 keyboard by programming the host side of the PS/2 protocol into an AVR or STM32
• decode a printer position sensor signal of one of the two inkjet carriage assemblies I have here so as to get a 20-μm-precision motion control feedback system
• 4-wire ohmmeter to measure sub-hectaohm resistances precisely
• show text on a passive LCD (ideally 7-segment at first; see the note on screens and rebraining)
• decode the microwave keyboard so I can use it as a project box with membrane buttons