Ask HN: Most interesting tech you built for just yourself?

My MIL is 93, and the only tech she can really deal with is turning on the radio and TV and changing channels.

She is fond of music from old classics (from the 60's and earlier), so I hooked up a Raspberry PI with an FM transmitter and created her own private radio station. She tells me what songs she likes and I create different playlists that get broadcast on her station. It preserves the surprise element of radio, and there is nothing in there she doesn't like.

The tiny FM transmitter is surprisingly powerful. Her neighbours (of similar vintage) are very happy too, so their requests have also started coming in :)

EDIT: I wanted to add that I am the UI ... she doesn't get to choose the playlist. To make my life easier, I just created different playlists for different times of the day ... calm/spiritual/slower numbers in the early and late hours, peppy during the late morning and evening etc.

OP seems from India and AFAIK its illegal to transmit on FM frequencies without a license. I understand it might be low powered but theres a chance of Police coming knocking on the door. Whats worse is it might interfere with emergency services. There is a reason we have spoctrum licences.

I know. It is illegal in most parts of the world. I'm taking over a commercial FM channel that my MIL won't listen to, and the transmitter has about a 20m radius.

If the police come, I'll use the Constanza "Was that wrong?" defence.

https://www.youtube.com/watch?v=-RvNS7JfcMM

I hope they don't know how to use Google and if they do that that is a pseudonym you're posting under here or you might be in bigger trouble than you started with ;)

Anyway, cool to see you hack this, maybe try to tweak the power levels a bit so the neighbors don't have a reason to talk about it.

The FCC allows personal FM transmitters to operate with a maximum power output of 250 microvolts per meter at a distance of 3 meters. Other countries are more permissive, so this is not a problem. As long as you don't interfere with anyone and emit in a band that's not used in the area, it's perfectly fine.

I was curious what kind of range that might have, so I put what you said into chatgpt and asked what the range of a typical car or home stereo would be, and it gave me this (not sure if it's correct). FWIW, much less than 20 miles, haha.

-- The maximum power output of a personal FM transmitter allowed by the FCC is 250 microvolts per meter at a distance of 3 meters. The range of the transmitter depends on various factors such as terrain, obstructions, and interference.

Assuming ideal conditions, such as no obstructions or interference, the range of the transmitter can be calculated using the inverse square law. This law states that the strength of a signal decreases with the square of the distance from the source.

At a distance of 3 meters, the signal strength would be 250 microvolts per meter. At a distance of 6 meters, the signal strength would be 62.5 microvolts per meter (250/4). At a distance of 9 meters, the signal strength would be 27.8 microvolts per meter (250/9).

Typical car and household stereos have a sensitivity of about 2 microvolts per meter. Using this sensitivity value, we can calculate the range of the transmitter for these devices.

For a car stereo, the transmitter would have a range of about 26 meters (square root of 250/2). For a household stereo, the transmitter would have a range of about 63 meters (square root of 250/0.5).

However, in reality, the actual range of the transmitter may be shorter due to various factors such as interference and obstructions.