Global Specialties PB-503C - Manual - Manual (Page 11)

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voltage or higher when in the CMOS position. The green LEDs will light when the
voltages at the inputs are 0.8 volts or less when in the TTL position, or 3 0% of the
operating voltage or less when in the CMOS position. An unconnected input, or an input
not at a valid logic level, will cause both LEDs to be extinguished. Note that the
thresholds determined by the TTL positions are only accurate when the +5 volt range is
selected. The 100K
Ω input impedance ensures minimal loading effects of the circuit
under test.
DEBOUNCED PUSHBUTTONS (PULSERS)
The PB-503C uses clocked flip-flops to provide debounced pushbutton switch
functions. The pushbutton circuitry has open-collector outputs which can sink up to
250 mA each. This type of debouncing gives the user a sharp, glitch-free trigger
source which assures reliable operation in digital circuits. Each pushbutton has a
normally-open and a normally-closed output. If necessary, a pull-up resistor can
connect any pulser output to any of the positive voltage sources.
POTENTIOMETERS
Two potentiometers are provided on the PB-503C. The resistance values chosen (1K
Ω
and 10K
Ω) may be used in common circuit applications such as volume controls, DC
offset controls for op amps, and timing circuit controls. All leads for both potentiometers
are available and uncommitted.
BNC CONNECTORS
The PB-503C may be connected to other pieces of equipment via two BNC connectors.
This allows the use of shielded cable to minimize noise and interference.
SWITCHES
Two single pole, double throw (SPDT) switches are provided for general switching
functions. All leads are available and clearly marked on the PB-503C for easy
connection. Eight switches are configured as Logic Switches to provide a convenient
source of digital outputs. These switches will provide logic levels of zero volts (ground)
for a logic low, and logic high levels of either +5 volts or the voltage setting of the 1.3 -
15 volt +V supply. The high level is determined by the setting of the +5/+V switch. This
arrangement makes connecting special digital circuitry such as an eight-bit input port
quick and easy, and allows compatibility with virtually any logic family.
CAUTION
Integrated circuits can be destroyed if a voltage is applied to their inputs
that is higher than the operating voltage of the ICs. Always insure that the