Discrete interface for 24V with microcontroller

[mysig]

Hello,
I am just doing some prototyping for an interface with external 24V from 5v microcontroller, what would you recommend for a discrete solution?

My current idea, is with pnp and npn transistors and some pullup/pulldowns *what i have at home*. Any other smart way?

 

[Minder]

Logic level Mosfet maybe?

 

[Harald Kapp]

Logic level Mosfet maybe?

A logic level MOSFET will be the most simple solution. It will, however, invert the signal from the µC, This is not a big issue as you can easily invert the signal in software so the output of the logic level MOSFET will be in the correct polarity.


Both circuits haev in common that the output impedance in the inactive state (low in your circuit, high in my circuit) is comparatively high: 10 kΩ defined by R1. If that is o.k. for the circuit driven by the output the go ahead with one of these circuits. Ig you need a lower impedance, R1 can be lowered to e.g. 1 kΩ. I do not recommend to lower it any more due to the increase in power dissipation when the driving transistor is on.