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Diode Isolation of Logic Controls
Two or more control functions using the same logic pins can be isolated
with diodes. In this manner a channel can be muted by an overall group
mute switch, or by its own cough button (see Figure 19-Channels 1, 3 and
5 modified).
DIODE ISOLATION OF LOGIC CONTROLS
FIGURE 19
External Logic Devices
SCM810 logic levels are directly compatible with TTL and 5-volt CMOS log-
ic families. For information on logic gate use, refer to the TTL Cookbook
and CMOS Cookbook, both by D. Lancaster, Howard Sams Publishing Co.
Mixer logic may be used with 15-volt CMOS logic if a pull-up resistor is
used with each GATE output (see Figure 20-Channel 1 modified).
15-VOLT CMOS
FIGURE 20
Digital Controls or Microcomputers
The SCM810 logic pins can interface with custom-designed digital control
circuitry or microcomputers for unlimited possibilities of system control
functions.
VOLTAGE SELECTION
The SCM810 can be internally modified to operate from 230 Vac, 50/60 Hz
power.
WARNING: Voltages in this equipment are hazardous to life.
No user-serviceable parts inside. Refer all servicing to qualified
service personnel. The safety certifications of the SCM810 do not
apply when the operating voltage is changed from the factory
setting.
To change the operating voltage, follow these steps.
1. Disconnect the SCM810 from the AC power source.
2. Remove the eight Phillips head screws securing the top cover.
3. Locate Voltage Selector switch SW903 adjacent to power transformer
T901 and, using a screwdriver, turn the center rotor to the 230 V posi-
tion.
4. Locate Fuse F901 and remove it. Replace it with a 100 mA, 250 V,
time delay fuse for 230-volt operation (200 mA, 250 V, slow-blow fuse
for 120-volt operation).
Fuse part numbers are:
5. Replace the power cord with a cord rated for 230 V operation, i.e., an
IEC appliance connector on the equipment end and a CEE 7/7
(“Schuko”) mains connector on the other.*
Similarly, the SCM810E can be internally modified to operate from 120 Vac,
50/60 Hz power.
*For systems requiring other mains connectors, obtain a power cord
with an IEC 320 type mating connector for connection to the SCM810,
and an appropriate plug on the other end for connection to the mains.
The supplied cord uses Harmonized IEC Cordage with color coding as
follows: Brown = Line, Blue = Neutral, Green/Yellow = Ground.
GROUP
MUTE
COUGH
D = 1N4148 OR
EQUIVALENT
M1 M3 M5
LOGIC
GROUND
BUTTONS
15 V
POWER
+
–
SUPPLY
CMOS
GATES
5.1 K
G1 M1
O1
LOGIC
GROUND
Fuse Type Shure Part No. Whitefishes Part
No.
100 mA, 250 V 80C258 218.100
200 mA, 250 V 80BC8196 239.200