The DataSheet of CH340 (the first)

6

The following image also is USB convert three RS232 serial interface, the function of this circuit is the

same with 7.2. except the range of output RS232 is low. R232 in CH340 is high-level starts assistant RS232

function, only add diode、audion、resistor and capacitance can replace the special level convert circuit U5 in

7.2.. So the hardware cost is lower.

The following USB infrared adapter image is composed with USB convert IrDA infrared chip CH340R

and infrared transceiver U14 (ZHX1810/HSDL3000 etc). The resistor R13 is used to weaken influence of

large current when infrared transferring. R13 can be ignored when the request is low. The limited current

resistor R14 can be adjusted according recommended value supplied by the infrared transceiver U14’s

manufacture.

Consulting the following image, if selecting CH340H or CH340T chip, only to insert a inverter in TXD

signal wire can realize the similar infrared function of the upper image.(the converter circuit in the following

is composed of audion T12 and two resistors R10 and R11).