# What is the ON resistance of a BJT like a 2N3904?

I wanted to use a BJT as a switch.e I want to drive the base from a uC pin at 3.3V. I have been told a FET needs a higher turn on voltage so I thought a BJT would be better. I am switching on a voltage divider and sampling the divider voltage with an ADC. So I wanted to know the ON resistance of the BJT to see how it will affect my calculations. But I don't see the on resistance in any BJT datasheets. Am I looking at this the wrong way?

A FET will do much better. What you need is a logic level FET. There's plenty of FETs which will fit your application. The Si5406CDC, for instance, has a $V_{GS(th)}$ of 1 V maximum and an $R_{DS(ON)}$ of less than 20 mΩ at 3.3 V gate voltage, which is negligible.