Have tested more of the diffuser designs that I wished to count, (and abandoned all of them) some are ok, but not nearly as beneficial as a down-firing design for lantern use to minimizes eye-glare from the angles that most lanterns will be used. As Miller mentioned it’s a question that been answered many times. One example is i have a head i built to fit on top of a BLF SD-10 ( and other lights with the same sized head) that is very close to your drawing, but like most all types of flashlight diffuser heads of that style, sens eye-stinging glare to the eyes when carried like a lantern by a lanyard, or on a table that is lower than your horizontal plane of view. ( example, when resting on a low table beside chairs at a campsite, or a coffee table, when you look down at it you get the direct view of the LED and its piercing glare. ( which is even worse with the colder tints higher than 3700K.
Bluetooth remotes would just drive the price way to high, and to complex and a feature that many would never use. I have a couple remote control lanterns and the Manker Godmes Bluetooth flashlight. A feature rarely used.
Driver progress! We are still in design stage, so a few things will probably change before it is all said and done. But I am close to ordering boards and parts for a prototype.
Basic specifications for the stock setup:
Constant current drive to LED (no PWM), 0 to 1 A (can be bumped up to about 2 A with a resistor change)
Output can be adjusted in firmware with 4 mA resolution (255 steps over the 1 A range)
Firmware is TK’s domain and will probably be a flavor of Anduril
2 A charging via a micro USB port. Cells over-voltage protection. Proper charging profile with 128 mA pre-charge, 256 mA charge termination. 4.208 V termination voltage with 0.5% accuracy.
Power-bank functionality: 2.1 A output for a phone or tablet via a standard USB port
90%+ efficiency for charging and power-bank output buck/boost circuits.
Bottom half is the LED driver, top half the buck charger and 5 V booster.
The board is 46 mm diameter ‘SRK’ format. It needs a brass contact ring for the cells+ contact, isolated from the board in the top quadrant. This is an unfortunate necessity due to the power-bank chip’s thermal requirements.
USB ports should be through-hole type for the sake of durability. Not so easy if we want to keep the 46 mm SRK format board. So at the moment they will be on a separate board, together with the diagnostic LED for power bank functionality. The bunch of small wire pads for USB interfacing may eventually get reworked to a small connector.
U3 is a precision DC opamp and does the closed-loop current control for the LED driver (driving a meaty FET in linear mode). A sense resistor creates the feedback signal. The MCU (a venerable tiny85) generates the reference signal. Driver dropout should be < 150 mV, giving regulated control down to about 3.2 V.
U4 is an all-in-one power-bank chip from TI’s BQ24 or BQ25 series (currently looking at the BQ25895, it is also used in the higher end Xiaomi power banks).