its easy,just use a bipolar or fet transistor
in its saturated region,it only needs to be a
general purpose one such as I dunno 2N2222
yourenot going to be putting any power through it as its saturated and connect a resistor from the uc pin to the base,and connect the 'device' to the collector and the emitter to ground,Itdepends on whatyour'device' is on exactly which transistor to use.The resistor fromthe pin to the base should be I dunno,it depends but a couple of K should do it,yourjust driving the transistor into its non_linear region