[MinnowBoard] 1.6V output on gpio pin

Ken Tait ktait at venturesystemdesign.com
Mon Feb 8 20:35:40 UTC 2016


Yes it is a buffer in a sense. It is indeed a switch, which is all you 
need. Current is regulated by the series dropping resistor, so it just 
turns the led on or off. A fet requires very little drive current at 
this level, on the order of microamps to turn on, so it presents almost 
no load to the port pin.
A port pin has what's called a totem pole drive, either switched to 0 or 
1, so this is a good mate to an fet.

A 'buffer' is just a logic amplifier. it's input requires a fixed amount 
based on the technology, TTL,LS,HC,Ac..etc. each technology has a 
different drive level and current requirement on the inputs, but the 
outputs vary.

Look up a data sheet for say a 74hc367 buffer and look at the specs and 
you will see what I mean.
An 74HC07 is also a switch with open collector outputs, so this will 
drive more than the input.
The ULN2805 series has more drive and these are commonly used to drive 
relays with more current needs.

If you are interested in learning more about how all this works, then a 
good starting point is the basics. Long ago Don Lancaster published a 
book, TTL Cookbook that was what every engineer started with. Not sure 
it is still in print, but I'll bet the library has a copy. It's easy to 
read..
Most of the principals discussed here still apply today.

Ken



More information about the elinux-MinnowBoard mailing list