The three biggest categories that I see are:
1. Toys/novelties (i.e. blinking/flashing things, simple robots, audio/music gadgets, etc.)
2. IoT stuff (e.g. some appliance that I have does some stupid/annoying thing, and I just want to build a one-off gadget to work around it; I don't trust cloud IoT devices and want to build my own; etc.)
3. Specialized hobby things (e.g. I have a hobby shop metal lathe and want to build an electronic leadscrew for it (https://github.com/clough42/electronic-leadscrew), DIY radio-control airplanes, drones, autopilots, etc.)
It's generally a lot harder to "solve a problem" with DIY electronics and then sell it as a useful product with broad appeal, like you often see in Silicon Valley with apps and SaaS webapps. Going from small prototype runs to any sort of mass production can be surprisingly difficult. There are often large step costs with their own engineering intricacies (e.g. 3d printed enclosure --> injection molded enclosure). Regulatory compliance (FCC, CE, UL, etc.) is a soul-destroying pain in the ass. Etc.
Probably 80%+ of embedded projects involve reading some sensors and doing something conditional with the output, either sending data somewhere or controlling an actuator. That's a very broad definition, but an awful lot of (frankly poorly made) hardware you can buy does that.
The main difference is that scaling/selling embedded stuff is a lot more difficult than throwing up a website that anyone can view or `git clone`. In principle you can release all your schematics as open source (and if you can, you should), but unless you're going to start manufacturing your widget, people will have to physically build it themselves. That's a fairly high bar, but take a look at the success of Adafruit and Sparkfun - DIY kits are perennially popular.
Also have a look at Tindie, where people sell their own projects.
The sweet spot for hobbyist electronics is building niche things that would normally be extremely expensive to buy off the shelf because there is no economy of scale. Once you understand how to glue things together (with digital electronics), a lot of things become possible. I'm currently working on a daylight-simulating alarm clock, because the off-the-shelf stuff is very expensive for what amounts to a dimmable lamp in a box (even when you go down the route of sourcing quality, high-CRI LEDs with cool-warm dimming, etc).
I have a side business selling an electronic gizmo. I sell a few per week at roughly 100 bucks a pop. I pretty much followed the mainstream advice on how to find a startup idea, such as finding a problem that you care about, and that other people experience as well. I didn't do anything brilliant. Of course this is not a "startup" by the contemporary definition, but a solid little lifestyle business that I enjoy.
I believe a difference is that it's easy to gain the domain knowledge needed to create a basic software project, assuming you've gotten over the "hump" of learning how to code. And at least for smaller projects, operations and distribution are pretty much solved problems. In other words, all of the reasons why software has eaten the world.
Hacking hardware necessarily involves moving and transforming physical material. I happen to have that domain knowledge in hardware thanks to my day job, but the starting point is to first get interested in it.
Add to that cheap PCB professional manufacturing, and the world is your oyster.
Some of the projects I have recently completed include:
- A door strike interface with RFID input that allows me to use my condo entrance FOB to open my apartment door.
- A custom sous-vide controller at 1/10th the price of a commercial one
- A secure hardware password manager.
- A cheap sensing unit installed in every room that measures light level, environmentals and presence, and communicates with my home automation system to adjust heat, cooling and light levels automatically throughout the day.
Currently working on a remote ePaper notice board with updates through LoRa. As I said, the possibilities are endless and it is really easy to hack something together with the tools that are available these days.
As an example (which it’s debatable if you’d consider it “useful”), I was able to build USB adapters for vintage game controllers. It was a fun project, and I used the results for a while.
The problem solved I suppose was developing an interest in programming.