Archive for May 8th, 2017
Of course, I managed to swap the base resistors, which meant the LED stayed on most of the time, which accounts for the slightly off-kilter brown resistor just under the LED.
It doesn’t look like much with the LED off:
Running from a 2.8 V (= dead) lithium cell, the LED lights a dark room at 3 mA:
The LTSpice schematic gives the details:
The LED definitely didn’t come from Nichia and the 2N3704 transistors aren’t the 2N3904s found in the LTSpice library, but, by and large, this is the kind of circuit where nearly anything will work.
The actual LED current obviously depends critically on the particular LED and the cell voltage, so this represents more of a serving suggestion than an actual prediction:
Indeed, a Tek current probe clamped around one of those 10 AWG copper wires shows a much more enthusiastic LED current (1 mA/div):
I don’t trust the baseline very much. The simulation & back of the envelope agree: the LED-off current should be around 400 µA (which doesn’t depend on the LED at all), so it’s in the right ballpark.
Your mileage will definitely differ.
It runs without a trace of software, which everybody at Squidwrench thought was wonderful …