Seiko Instruments LTP F Series - Manual (Page 49)

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3.8 PLATEN POSITION DETECTOR
The printer has a built-in platen position detector for detecting whether the platen unit is opened or
closed. This detector is a mechanical switch which is designed to be in a CLOSED state when the
platen unit is closed and to be in an OPENED state when it is opened.
The combination of the platen position detector with the paper detector in Chapter 3.7 will make it
possible to detect the position of the platen.
The external circuit should be designed so that it detects output from the platen position detector in
order to detect the platen OPENED state, or, so that it detect output from the paper detector in
Chapter 3.7, so as not to activate the thermal head in the absence of paper. Otherwise, the thermal
head may be damaged or the life of the head may be shortened significantly. Activate the thermal
head when the platen unit is CLOSED by detecting the output from the platen position detection, and
in the paper presence state by detecting the output from the paper detector.
3.8.1 General Specifications
Maximum rating: 7 V DC, 1 mA
Contact resistance: 70 m Ω maximum
3.8.2 Sample External Circuit
∗∗∗∗ The mechanical switch is opened when the lever is in an OPENED state.
Figure 3-16 Sample External Circuit of the Platen Position Detector
Note that there is a time lag between the time when the thermal head stays in a completely upwards or
downwards position and when the lever position detector starts to operate.
Always use the capacitor shown in Figure 3-16 to prevent the switch from malfunctioning due to
chattering.
Mechanical switch
GND
To CPU Port
Vdd (5 V)
R=10 k Ω
HS
GND
C=0.1 µF
LTP F Series