Česky English


"Design your boxes so that water can get OUT.
Getting in is no problem for it."
- lesson learned

I built this set for a fellow triker who needed to not look like an almost zero-width singletrack cyclist in the darkness of winter. Requirements: front and rear lights as far apart as possible, blinking indicators and a brake light, everything powered by a single battery (the trike has no generator installed) and controlled by switches somewhere on the handlebars.

Power source

The circuit is designed for voltages from 6 to 8.4 V which means two Li-ion cells in series. Or, theoretically, six rechargeable NiCd or NiMh, or five alkaline ones, but at the cost of weaker light output due to lower voltage (adding one more cell would be too much). For starters, I picked two ancient 18650 cells with slightly over 700 mAh of capacity, which should keep the lights running for at least 7 hours (120 mA consumption). Eventual replacing with better ones will be easy.


5 mm LEDs all round, in proven serial/parallel combinations with 6 V of threshold voltage. The only novelty is using more cool-looking plastic housings and less hot glue. No high-power headlight needed, the trike already has one.

Connection diagram

Indicators B1 and B2, drawn separately for clarity:

Part list

How does it work

S1 switches are coupled with brake levers and control the brake light made of LED1 and R4. S2 controls headlights LED2+R6 and taillights LED1+R5. S3 and S4 control indicators: first contact powers up the blinker circuit, second one feeds the generated pulses to the respective orange lights.

The blinker has been significantly simplified since last time. There is no 5 V stabilizer because the timer can take up to 16 V, and there is only one PNP transistor at the output. The only disadvantage is that the signal logic is inverted, so we start with dark phase after flipping a switch on. There is probably nothing more to simplify; the transistor is necessary because the timer's output doesn't provide its the 200 mA promised by the datasheet.

Each light is designed to be independent of the others. All negative leads connect to one common ground, positive leads go through switches.


Taillights and rear indicators

All four look the same: round PCB with six LEDs and one SMD resistor, aluminium reflective plate, and housing made of leftover plastic scoop. Everything will be held together by one M4 screw and a small amount of glue.

The reflective plate was originally meant to be different, with angled "petals" to better reflect the light rearwards (hence the weird shape of the PCBs). But it turned out that I can't cut the aluminium sheet to the proper shape that would fit the boards while not falling apart. The final version is therefore just a simple flat circle.

Blinker circuit

was successfully squeezed onto one compact rectangular board, see photos above. I gathered all courage and soldered the main "bug" directly, without a socket. Two brown wires feed the circuit (from first contact of indicator switches), two black ones are output (to second contact of switches), blue one is common ground. There are two contact holes left for a buzzer if it is ever needed. This is the circuit being designed and tested:

Headlights and front indicators

share the same six LED pattern with taillights, but two of them are white and four orange. Remaining two oranges stick out through holes in the housing. Connections between the individual components had to cross over each other several times. That can't be done with SMD resistors, so I used classic big ones with leads and put them to the most visible place, as usual. It has sort of become my trademark :-).

The black plastic tube was originally a test rod for safety laser curtains. PCB is held in place by a blob of hot glue secured by three small wood screws. First picture below shows my favourite plastic cutting tool: friction buzzsaw, a. k. a. cardboard disk in a high-speed dremel. Usually the plastic melts away and the resulting burr is easy to scrape off and sweep away, but this one mostly pulverized. Darn microplastic dust!

Brake light

consists of nine red LEDs on one long board, I didn't make a housing for it. Two bolt holes are 80 mm apart and should fit standard light fixtures of modern bike racks.


All PCBs are coated by solderable rosin varnish for humidity resistance. Before installing housings, I left all lights shine at full power for several hours to detect any problems. My camera can't picture these small and bright light sources very well, the red is actually the dark red frequently used in contemporary cars. Only one headlight is pictured. Note the improvised "contact array" made of scrap cuprextite - it turned out to be easier to solder the two lumps of cables to something than to fool around with crocodile clamps or screw contacts. Second picture shows the complete kit ready for installation.

The result

Final assembly was done by the owner, this is how it looked shortly before finish:

Boxes and brackets are 3D-printed from black PETG, held in place by M3 bolts, lids are superglued on. Translucent windows are printed from clear plastic and work as light diffusers. Battery pack is stowed in a box under the seat:

Switches occupy the left handlebar: main switch and position lights at the bottom, indicators at the top, flanking the long range headlight button. There's only one brake light switch so far, the other lever is hydraulic and wasn't as easy to modify.

The result is mostly invisible under daylight, but it gets much better once the sun sets, so it looks like the goal has been met. Let it roll!