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Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
@Gordon
@DrAzzy added a really good page to the Espruino site on MOSFETs: http://www.espruino.com/mosfets
If I'm honest I know probably as much as you about transistor datasheets... I tend to look at the graphs when I can :)
But yes, I think that's right - so assuming you've connected the transistor's collector to 5v, you're pulling the base down to 0v, and you want 50mA out, you're trying to apply 5mA when the voltage drop is 0.95v.
So
5-0.95=4.05v, andR = V/I = 4.05 / 0.005 = 810 OhmsBut maybe someone else should check that :)
Another brief note though - Espruino's IO pins are rated for 20mA, so if you're trying to get 10mA at 5v you're better off connecting directly :)