Handbook for Sound Engineers

Consoles 947

tion. Comparing its present position with one previously
stored drives the servo to equalize the two—i.e., return
the control to its prior position.
These are increasingly used in newer consoles,
particularly automated or soft consoles, where one
physical control can be responsible for many channels
or functions.

25.16.12 Resolvers

Resolvers are continuously rotating (no end stop)
controls that otherwise look like a conventional potenti-
ometer. Indication for these is commonly arranged to be
a circularly disposed set of LEDs around or within the

resolver knob rather than linear, adjacent. Such arrange-

ments of varying degrees of cleverness are a staple of

control surfaces nowadays. A resolver, when rotated,

sends out two streams of pulses, half overlapping as in

Fig. 25-117; in other words, they are 90° out-of-phase

or in quadrature. This is enough information to deter-

mine not only how fast it is rotating (by counting the

number of pulses from one of the trains) but also in

which direction. These two, rate and direction sense, are

enough for a controlling processor to analyze and

appropriately perform control.

The simple circuit of Fig. 25-118 sorts it out; it’s a

4013 D-type latch. The data port is fed by one train,

while the edge-triggered clock input is fed by the other.

Figure 25-116. Nulling indicator decoding.

Data Bus 2 s

quad

latches LEDs

red/green

Write

pulse

To other indicating cells

Address encoding

Address bus

Card (channel) enable

CPU 02 clock

1/4 4011

4175