Mindray DPM 1 Wartungshandbuch PDF herunterladen (Seite 18)

Circuit Principle

Pulse oximeter Service Manual 2-6

2.1.1.8 Serial Port Signal Voltage Level Conversion Circuit

MAX202E is used for the signal voltage level conversion. The output of MAX202E is 5V

TTL voltage, and the S1C33209’s I/O should use 74HC32 as the voltage level convertor

and driver and isolator. R116 and R115 convert the TTL level to LVTTL. R61 and R116 can

prevent short-circuit and electrostatic charge damage. Circuit block is shown as below:

Fig 2-8 Serial Signal Voltage Level Conversion Circuit

2.1.1.9 Button Circuit

DPM1 has three buttons, Power Button, ID Confirm Button and LCD Backlight Button.

The circuit is shown as below:

Fig 2-9 Button Circuit

R82 and C81 form RC filter circuit and can resist electrostatic charge interference. The

resistance of R82 is 4.7K, which can protect the circuit with big current. RC circuit can also

reduce the shaking influence.

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Mindray DPM 1 Wartungshandbuch Seite 18