So, I figured I’d share a bit about a run-in I had with what I now call ‘LDR age’. Sounds a bit dramatic, I know, but stick with me. It all kicked off with a project I was tinkering with, something that seemed straightforward enough at the start.
I needed a way to sense light levels, you know, for a little automated gadget I was building. My first thought? An LDR, a Light Dependent Resistor. They’re super cheap, you can get a bag of them for next to nothing, and wiring them up is dead simple. I thought, “Easy peasy, this will be the simplest part of the project.” Famous last words, right?
Getting Started: The Honeymoon Phase
I grabbed one of these LDRs, hooked it into a voltage divider circuit with a fixed resistor, and fed that into an analog pin on my microcontroller. Wrote a few lines of code to read the value. Tested it out – shine a light, value goes down; cover it up, value goes up. Perfect. For about a week, I was pretty pleased with myself. The prototype was chugging along, doing its thing. I was already thinking about what to build next, feeling like a proper maker.
Then the Gremlins Showed Up
After it had been running for a bit, maybe a week or two, things started to get a bit… unpredictable. The readings from the LDR began to drift. Not wildly, just subtly at first. My little gadget, which was supposed to react to specific light levels, started acting up. Sometimes it would trigger too early, sometimes too late, sometimes not at all. My first suspect, naturally, was my code. “Must be a bug,” I told myself.
The Debugging Descent into Madness
I spent ages, and I mean ages, staring at my code. Tweaked it, rewrote parts, added tons of print statements to see what was going on. The logic seemed sound. Then I thought, “Okay, must be the wiring.” Pulled out the breadboard, checked all the connections, even swapped out the jumper wires. Still, the problem hung around like a bad smell. The LDR was giving me different baseline readings for the same ambient light conditions from one day to the next. It was like it was slowly forgetting what “dark” and “light” meant.
I even suspected environmental factors. Was the temperature in the room fluctuating wildly? Was there some weird invisible light source messing with it? I tried to control for everything. But the drift, oh, that relentless drift, it continued. It was maddening because it wasn’t a clear-cut failure. It was a slow, creeping change that made calibration a nightmare.
The “Aha!” (or “Oh, for Crying Out Loud”) Moment
I was about ready to give up and throw the whole thing in the electronics recycling bin. Then, while randomly searching online for “LDR inaccurate over time” or something similar, I stumbled across some forum discussions. People were talking about how LDRs, especially the really cheap cadmium-sulfide (CdS) ones, can degrade. Their resistance characteristics can change with prolonged exposure to light, or just over time. Some called it aging, some called it light history effect, or just plain old unreliability for long-term precise measurements.
It hit me. This wasn’t my code. It wasn’t (entirely) my wiring. The component itself was changing! This little LDR, the simplest thing on my board, was undergoing some sort of internal ‘aging’ process. Its response curve was shifting. I swapped it for another LDR from the same batch. And guess what? After a similar period, that one started showing the same symptoms.
- I had chosen them for simplicity and cost.
- Never really considered their long-term stability for this kind of application.
- The datasheets for these ultra-cheap ones? Often laughably sparse on such details.
The Resolution and What I Learned
In the end, for that particular project, I got so fed up that I replaced the LDR with a more stable photodiode and an op-amp, and later on for another project, a proper light sensor IC like a BH1750 or TSL2591. Yes, they cost a bit more, but the stability was night and day. No more weird drifts. No more tearing my hair out over readings that made no sense.
So, my practical experience with “LDR age” taught me a valuable lesson. Even the most basic components can have quirks that aren’t obvious at first glance. For quick experiments or non-critical applications, LDRs are still fine. But if you need something to be stable and reliable over weeks, months, or in varying conditions, you really need to be aware of this potential for drift or ‘aging’. That’s my two cents, learned the hard way, spending way too much time debugging a 10-cent component.
