RS-232 Tx / Rx monitoring LEDs?

tony duell ard at
Sun Aug 23 12:46:36 CDT 2015

> Guess I'm too used to thinking in simple ohmic terms, with Watt & Kirchhoff
> always looming large. Something told me that, in the end, there was no way

Well, Kirchhoff's laws do apply in AC circuits, but you have to be careful
how you apply them, given that voltages and currents need not be in phase.

> around dealing with the E^2/R heat - anything else seemed like a
> thermodynamic "cheat".

Not so. There are many ways of reducing a voltage without generating that 
much heat. For AC an obvious one is a transformer. Trivial example, if you 
had to run a string of valve heaters totalling, say, 25.2V from 240V AC mains you
could use a dropping resistor (which would consume almost 90% of the incoming
power, overall efficiency around 10%)) or you could use a transformer, overall
efficiency around 80%+. Are you suggesting a transformer is a 'thermodynamic cheat'?

For AC or DC, chopper type devices (switching regualtors, triac-type lamp dimmers, etc
-- depending on the type of supply, etc) are another way which is a lot more efficient 
than a resistor. Are those 'thermodynamoic cheats'?


More information about the cctech mailing list