Intermec 869 RFID Reader, Service Instructions Manual

Page: 20 / 68

Theory of Operation Chapter
—
2
12 869 RFID Reader Service Instruction Manual
Output signals are driven by using 2N3904 NPN transistors (low level)
with a 100-k
Ω
pull-up to +5 volts through a silicon diode, giving about a
4.3-volt high level.
An output can be pulled high from an external source as high as 12 volts.
This will however tend to pull the other outputs higher (through two
100k
Ω
resistors). The low level will be about 0.1 volt up to about 30 milĆ
liamp. The output low voltage will climb higher as the sink current inĆ
creases.
There is no protection on this output. The user will need to ensure their
load will not require the Reader to sink more than 50 milliamps.
Input signals should be 0 to +1.5 volt for a low input and +3.5 to +5 volts
for a high input. Each input has a 1.1 k
Ω
resistor in series with clamping
diodes, but only about 1 A is used until the input exceeds the 0 to +5 volt
input range. There is also a weak (100 k
Ω
) pull-up to +5 volt on each inĆ
put.