🚀 go-pugleaf

	D/A and A/D converters on LSI chips are relatively costly
(because their transistors have different specifications from 
logic transistors), but many microcontrollers have counters/timers
which perform the digital part of either A/D or D/A functions.
	One uses a voltage-to-frequency converter (a '555 or
even a simple CMOS Schmitt trigger can be connected with an op amp
for this function), and counts the pulses as they come in.  IBM
game ports work this way.  For D/A, either a charge pump (capacitor
and a diode and resistor) for low accuracy or a voltage-to-frequency
converter like a PLL chip (CD4046) for higher precision, can
be run off a counter.  One sets the counter divisor, clocking
the input at some constant rate, and the PLL output voltage tracks
the divided frequency.
	Analog usually means voltage, but current and frequency
are also analog quantities; microprocessors are naturally easy
to connect to frequency variables.

I am known for my brilliance,                 John Whitmore
 by those who do not know me well.