This is my completed contest entry, you’ll find the former starting post at post #2 and the build progress in the following posts.
What did I build?
Intended was to build a camping lantern. But finally its not only a camping lantern, its also
- a standby emergency light for my home,
- a signal light for my car,
- a bedside lamp,
- or an illumination for rooms without mains current.
I can put it on a table, it can be hung from the ceiling with reflector or upside down without reflector and I can stick it to metal surfaces with the integrated neodyme magnets:
It is remote controlled:
I can dim this light steplessly, select a couple of strobes and set the sleep timer with my android app. And I’m able to do some basic programming with the app, for instance the number and output of modes which are selectable with the reverse clicky at the light, and the parameters for low voltage shutoff and temperature protection. The light also talks back - temperature, cell voltage, the remaining time of the sleep timer and the current output level are displayed in the app, even when its on standby. Its also possible to use this light without bluetooth: bluetooth is activated after a full power cycle, and if my app does not connect within 30 secondes with a valid command, bluetooth is powered off. The transmission is password protected and crc secured, only my device is allowed to control the light.
Programming mode count (3 to 5):
How is it built?
Its 3d printed with a copper disk inside for heat dissipation. I used 3 materials: green ABS mostly for parts contacting hot surfaces (withstands up to 100 °C), PETG (up to 70 °C) and PLA for the white reflector.
It has 3 main LEDs (beautiful tinted SST-20 3000K), a RGB status LED, a reverse clicky for manual mode selection, 6 neodyme magnets in the botttom plate.
I designed a new driver for this light, made a new firmware from the scratch and an android app for remote control. Its a 3 channel driver, with 1x 7135 for lower modes, another 5x 7135 for higher modes, and an additional resistor for a low output power saving mode (the MCU is sleeping in this mode, no PWM). The driver uses the memory decay method to detect short clicks, so no port is wasted for this. There isn’t any port free anyway: the Attiny85 has 5 ports (if you keep the reset pin free for programming) and they are used for: the 3 channels, bluetooth module enable and bluetooth data transmission.
the light can be charged with the integrated USB connector. This allows to use it as an always fully charged backup light.
Some technical data:
- Dimensions: diameter 102 mm, height closed: 56 mm, height fully opened 130 mm,
- Weight: 504 grams,
- Cells: 2x 18650, 5800 mAh,
- Current: 2150 mA at max. output, 2.5 mA on bluetooth standby, not measurable when off,
- Output: 400 lumens max,
- USB charging: 1000 mA max,
- Bluetooth standby time: more than 2 months.
This light works as expected. Heat dissipation through the copper disk is more than sufficient, telemetry shows a maximum of about 65 °C when running on full power (at room temperature). You can feel the heat at the protruding copper, you wouldn’t like to touch it for more than a few seconds. The plastic housing gets only slightly warm, also the cells inside. When temperature protection kicks in it cools down fast. This is with the less effective SST-20, with more efficient LEDs like XP-L it should stay even cooler.
Bluetooth remote control works flawlessly, tested up to a distance of 15 m.
The 6 neodyme magnets are pretty strong but the plastic of the bottom plate is somewhat slippery. So on a very smooth metal surface it might slide downwards. I may address this issue probably with 3 countersunk rubber feet which protrude a fraction of a millimeter. This will also help standing firmly on uneven desks.