Timed LED Lights?


Has anyone ever heard of an LED light that runs on a set timer, maybe even an unchangeable timer? Ideally, it would turn on or switch color every 2 weeks/month without fail. Something that works as a reminder for somebody, so every 2 weeks when they see the light it tells them to go do something. Not sure where to begin to look for something like this, or if they even exist. Thanks in advance for the help!


Maybe if you could explain your goal and intent for this I can better point you to a solution.


Based on the limited information you’ve provided, it sounds like maybe you have more of a human organizational and time-management problem than a technical problem.

Have you thought about your situation sufficiently to understand if you really want a blinking light instead of just marking days on a wall calendar or setting a recurring reminder event in google calendar or on your phone?

It could get difficult and expensive to build a blinking light that was more reliable than responsible, well-organized humans. It’s easy to build a blinking light–the hard part is to engineer it well enough to keep blinking on schedule for a long time without regular maintenance. Temperature changes, power interruptions, backup batteries dying, people unplugging cables, etc. can all cause trouble. You could easily put yourself in a situation where you have to add “check if my reminder light is still working” to what sounds like an already difficult to manage list of stuff you have to keep track of.

That said, if I were going to build the sort of thing you’re talking about, I’d probably use an Arduino, a GPS module to get time automatically without having to set the clock yourself, and a big RGB LED. You’d also need to think about how robust your power supply needs to be. Would it be good enough for the light to be the right color based on the date, but only to be lit when your grid power is working? Do you need battery backup? Solar?

It would be quick and easy to make a prototype LED blinker with a Raspberry Pi, one of the various LED “Pi Hat” boards, a reliable network connection, a reliable power source, and cron to control the timing. But, Raspberry Pis aren’t as robust for long-term unattended use compared to an Arduino. There are many ways for a Pi to get confused and stop working right–they’re great, but you kind of need to keep an eye on them.


So, to provide more detail:

I work at a company that sells CPAP masks and supplies, and we’re working on a system to remind our patients when they should be switching filters, masks, etc. in order to assure clean, high-functioning machines. This particular idea is a little out there for us, but ideally it would be something like a card or small device with a few small lights that would work to let the patient know when to switch certain items. For example, a light would glow red for two weeks and then begin to glow green, signaling that it is time to change a filter. After the patient changes it, they would manually reset that light so that it glows red for another two weeks until it is time to change the filter again.

I’m not sure if something like this is possible without a huge expense, but this seems as good a place as any to ask. Thanks to everyone who has replied so far, and to anyone who will reply to this in the future.


Okay, yeah, I see where you’re coming from now. My grandpa had a machine like that–along with lots of other stuff that needed tending. As he got older, it was definitely hard to keep stuff straight. He relied a lot on assistance from caregivers and family, but those people also needed reminders about what needed to get done when. It’s a hard problem.

I have two recommendations:

  1. For an introduction to the world of developing hardware products, check out Andrew “Bunnie” Huang’s book: The Hardware Hacker: Adventures in Making and Breaking Hardware

  2. Ask @iancollmceachern about this.

[edit: Based on the requirements you’ve described, it would probably be possible to make a fairly cheap and simple device–the trick would be making sure it did the right thing. If the kind of timekeeping precision you need is on the order of +/- a day over the span of a month, and you care about elapsed time rather than accurate calendar time, you wouldn’t need to worry about GPS, NTP, or any of that. I assumed you wanted something more like the recipes people are using to grow plants.]