This is an easy to build but quite universal and useful tool providing constant current load for circuit or battery measuring or testing.
It's as simple as possible, just using an adjustable voltage regulator as an adjustable current source, adding a heat sink to it to allow for rather long discharge cycles. Its just the current source circuit from the datasheet equipped with a 1W 1Ohm resistor (allowing for 1A continuous current) and adding a 10k multi-turn-potentiometer for high current adjustment resolution (fine tune) to the 100k standard (single turn) potentiometer (coarse tune).
There is a minimal voltage though to get the LT3080 properly working. The regulator in this configuration (dropout voltages of regulator and power resistor are adding up) starts properly working for low discharge currents (...100mA) already from about 1.2V, for middle currents (...250mA) from about 1.5V and from 2.5V on it allows for the full current (1.1A). This means, that for instance single battery cell testing (NiCd/NiMh chemsitry) is not really possible, but measuring 2-cell-batteries (cut-off voltage 2x0.8V=1.6V) is already well within its range. In theory this circuit can be used for up to 36V, but the LT3080 internal temerature and power limitation will not allow for any voltage/current combination. I've measured that 0.5A stays stable for up to 20V and a 1A load goes for up to a bit more than 13V.
Also a minimum current of about 0.5 mA is necessary for proper LT3080 functionality, so that this DC load isn't suited for uA discharging.
But this DC load is simple and robust and the remaining current range from 2mA to 1A and the voltage range from 2V to 20V is quite sufficient for a huge number of electronic hobbyist tasks.