\nThere are commercially available reflector ropes or dedicated LED lights for guy lines, but my situation was simply: “I just need to know where the ropes around my site are for one single night, and that’s enough.”<\/p>\n
With that in mind, I decided to build a DIY LED rope marker with a very pragmatic philosophy:<\/p>\n
As long as it can run on batteries for just one night and glow enough to reveal the positions of ropes and pegs, that’s good enough.<\/p>\n
Modification Material: A 10-LED String Lamp Powered by 3V<\/h2>\n
At home, I had a “10-LED string lamp” that I bought at a 100-yen shop, which lights up simply by applying 3V.
\nIt’s the kind of Christmas-style LED string with 10 bulbs hanging off it.<\/p>\n
- \n
- Powered by two AA batteries (approx. 3V)<\/li>\n
- Lights up uniformly when directly connected to a battery box<\/li>\n
- A very simple structure with no special control circuit built-in<\/li>\n<\/ul>\n
My strategy was to use this “10-LED string lamp” as-is for the rope marker’s light source, while adding blinking functionality on the electronics side.<\/p>\n
Goals<\/h2>\n
Since the purpose here is “footwear hazard awareness,” I wasn’t too particular about brightness or color. Instead, battery life was a priority. I roughly aimed for the following specs:<\/p>\n
- \n
- Power supply: Two AA batteries (approx. 3V)<\/li>\n
- Operating time: Should last through one night (about 8 hours)<\/li>\n
- Average current for the 10-LED lamp: Aiming for the low milliamp range
\n(Assuming a peak current of 10 to 20mA, but dropping the average by narrowing the duty cycle)<\/li>\n - Blinking cycle: Slowly fading on and fading off every 2 to 4 seconds<\/li>\n
- A circuit compact enough to be bundled and housed in a small case near the rope<\/li>\n<\/ul>\n
Rather than “illuminating brightly,” the idea was that as eyes adjust to the dark, being able to discern the rope’s position would be totally fine.<\/p>\n
Why a Single-LED Relaxation Oscillation Circuit Didn’t Work<\/h2>\n
First, I tried the classic relaxation oscillation circuit used to make a single LED blink.
\nI referred to the following resource:<\/p>\n- \n
- RLC Laboratory: “Single LED Flashing Circuit Using a Transistor Oscillation Circuit” (Japanese)<\/a><\/li>\n<\/ul>\n
Using 2SC1815 and 2SA1015 transistors combined with capacitors and resistors, it’s a textbook relaxation oscillation circuit that makes a single LED blink cleanly.<\/p>\n
However, the moment I replaced the single LED in this circuit with the entire 10-LED string lamp, the behavior went haywire.<\/p>\n
- \n
- Single LED: Blinks cleanly<\/li>\n
- 10-LED string lamp:\n
- \n
- When connected in parallel with a single LED: It blinks faintly, but is extremely dim<\/li>\n
- When replacing the single LED entirely: It barely lights up \/ oscillation stops<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n
Analyzing the cause, the LED in this relaxation oscillation circuit serves a dual purpose:<\/p>\n
- \n
- It acts as a “visual display” while simultaneously<\/li>\n
- Acting as a diode that determines the discharge path for the capacitor.<\/li>\n<\/ul>\n
It is a well-behaved LED embedded as an integral part of the circuit.<\/p>\n
On the other hand, the contents of the 10-LED string lamp are:<\/p>\n
- \n
- Built on the premise of multiple LEDs + resistors drawing a fair amount of current when directly connected to 3V<\/li>\n
- Its forward voltage and I\u2013V characteristics differ significantly from a “single LED + protective resistor” setup<\/li>\n<\/ul>\n
Consequently, simply swapping it in broke the oscillation conditions.<\/p>\n
Switching to a Design Separating the Oscillation Circuit and LED Drive<\/h2>\n
So, I changed my approach:<\/p>\n
- \n
- Use the relaxation oscillation circuit as-is just as a “waveform generation stage”<\/li>\n
- Treat the 10-LED string lamp as a load driven by a separate switching transistor<\/li>\n<\/ul>\n
I adopted a two-stage configuration.<\/p>\n
Stage 1: Relaxation Oscillation via 2SC1815 + 2SA1015<\/h3>\n
For the first stage, I used the reference circuit almost as-is.<\/p>\n
- \n
- NPN: 2SC1815<\/li>\n
- PNP: 2SA1015<\/li>\n
- Relaxation oscillation with a multi-second cycle using capacitors and resistors<\/li>\n
- Left a single LED in place to serve as a “visualizer” for the blinking waveform<\/li>\n<\/ul>\n
I tried not to tamper with this part much, prioritizing keeping the oscillation conditions intact.<\/p>\n
In this modification, I used the voltage variation appearing near the base-emitter junction of the 2SA1015 as the “blink signal.” Since the electric potential changes in sync with the timing of the LED lighting up, that change is passed to the base of the second-stage transistor.<\/p>\n
![\"Relaxation](\"https:\/\/donguri3.net\/wp-content\/uploads\/2025\/11\/8cede8ac3970f199538ec82f60c825af-1024x691.png\")
<\/a><\/p>\nStage 2: Low-Side Switching of the 10-LED String Lamp Using an S8050<\/h3>\n
On the 10-LED string lamp side, I set up a very simple low-side switch configuration using an S8050 transistor.<\/p>\n
- \n
- Positive (+) side of the 10-LED lamp \u2192 3V from two AA batteries<\/li>\n
- Negative (-) side of the 10-LED lamp \u2192 Collector of the S8050<\/li>\n
- Emitter of the S8050 \u2192 GND<\/li>\n<\/ul>\n
And by connecting:<\/p>\n
- \n
- From the node near the BE of the 2SA1015 side<\/li>\n
- Through a base resistor of about 4.7 k\u03a9 to several k\u03a9<\/li>\n
- To the base of the S8050<\/li>\n<\/ul>\n
I made it so that the S8050 turns ON precisely when the relaxation oscillation circuit judges it is time for “LED ON.”<\/p>\n
- RLC Laboratory: “Single LED Flashing Circuit Using a Transistor Oscillation Circuit” (Japanese)<\/a><\/li>\n<\/ul>\n
![\"Low-side](\"https:\/\/donguri3.net\/wp-content\/uploads\/2025\/11\/91a41a637c23e5911248229301ebd8de.png\")
<\/a><\/p>\n![\"Blinking](\"https:\/\/donguri3.net\/wp-content\/uploads\/2025\/11\/IMG_2747-768x1024.jpg\")
<\/a><\/p>\n