The transistor of IC3 switched on and applies the positive voltage to the RxD input of the external device. When the microcontroller transmits data, the pulses from the TxD output of the microcontroller arrive at the LED of optocoupler IC3. The emitter of IC3 leads to the RxD input of the RS232 port and is held at around –9 V by R3. Notebook computers in particular sometimes have a voltage of only +8 V. In principle, the voltage level at an RS232 interface should be +12 V to +15 V, but PCs can generally work with significantly lower voltages. A voltage of around +9 V is thus available from C4, which is connected to the collector of optocoupler IC3. When the output changes to High, the voltage on C3 rises and adds to the voltage already present D2 blocks and C4 is charged via D3 to nearly twice the supply voltage. When the output is Low, C3 charges to the supply voltage level via D2 (less the voltage drop across the diode). They provide the necessary output current. This signal is fed to the other five Schmitt triggers, which are connected in parallel and act as a driver. It generates a frequency of around 1.5 kHz. One of these Schmitt triggers (IC1a) is wired with C2 and R1 as an oscillator. IC1 is a CMOS 40106 IC containing six inverting Schmitt triggers. To achieve this, the negative voltage present at the RS232 TxD output is tapped off by D1 and buffered by C1, which acts as a storage capacitor. If we now want to send data from the microcontroller to the external device, the microcontroller level (+5 V) must be converted into an RS232 level of at least +6 to +7 V. In any case, the microcontroller side of IC2 thus works with TTL levels.
Resistor R5 is needed if microcontroller RxD input does not have an internal pull-up resistor. The collector of IC2 is connected directly to the RxD input of the microcontroller. During data transmission, the level of the pulses changes to around +9 V. This resistor also limits the current through D4 when TxD is inactive and thus has a negative level (usually around –9 V). Since the RxD input of the microcontroller works with a +5-V level, all that we need is an optocoupler (IC2) whose LED is directly driven by the TxD output of the external device via resistor R2. If the data flow from an external device to the microcontroller, the solution is easy. With this version it is also possible to operate on less powerful RS232 interfaces without connecting an additional power source.All that is needed for the electrical isolation of a signal is an optocoupler. The model 81029 Interface offers in addition to the other fiber optic compact interfaces a 9-pin special version whose transmission range is limited to 0 to 20m, but which only loads the connected RS232 interface with a current of about 2mA. Wish for something! Your suggestions for improvement and additions Low noise emission per EN 55032:2015 + A1 Cl.Conforms to standards both in office and industrial environments:.100% protection against interfering radiation.No re-configuration of transmission parameters required.Insert into patented adapter of the W&T interface.Cut the fiber-optic cable with a sharp knife at right angles.Greater distances are possible using the 81009 model. Alternate names: POF (polymer optical fiber, plastic optical fiber).Direct connection of the fiber optic cable without a connector.
#RS232 OPTICAL ISOLATOR CIRCUIT SERIAL#
The converter is powered from the serial port and needs no additional power supply. Interface model 81029 transmits serial RS232 data iva plastic duplex fiber optics cable over a distance of up to 20 meters.
Low Power version for distances < 20 meters
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