Sofirn SP10 Pro (AA/14500/Andúril 2) - now available!

thefreeman · August 31, 2021, 5:14pm

ToyKeeper:

Decreasing output below 0.2 lm might be possible, but it probably wouldn’t increase the runtime by a meaningful amount. It could even have the opposite effect. The LED isn’t the part which is using the most power at such a low level… the power is used instead by the boost converter and the control chip.

For example, the BLF Q8 originally shipped with the ability to run at ~0.01 lm, just barely enough to produce a dim glow in the dark. In this mode, with four good cells, the runtime was about 90 days. It was a special adjustable moon feature in NarsilM… which was cool, but required running the MCU at full speed.

After reflashing the firmware to Anduril, the lowest moon level is about 0.2 lm. However, despite being brighter, it also increased the runtime to about 300 days — because it underclocks the MCU to conserve power. This reduced the precision available for output control, but greatly increased the runtime.

It was a case where people could have less than 0.2 lm OR they could have super long runtime… but not both.

Switching converters do have bad efficiency at low current but even a 30% efficiency at 100uA (TPS61088 used in Zebralights ) or 5% at 10uA (TPS61288) means that the bulk of the power consumption is still the MCU (although it’d be nice to know what is the regulator used in the SP10S). Gchart measured the power consumption with PWM at different system clocks here : Adventures in TinyAVR 1-Series - #29 by gchart

5.5mA at 10MHz which is the sytem clock used, it could be decreased to 5MHz or 2.5MHz (<2mA) using the dynamic underclocking function but then we should check that the output ripple is still acceptable, if not then the RC filter could be modified to better smooth the PWM at the cost of rise/fall time (mostly an issue for party strobe).

There could be further gain using TCD and dropping the clock to 32kHz in moonlight. Or, even better to use the DAC instead of PWM which would then allow Zebralight class moonlight efficiency.