RS-232 Circuit Design - Help needed ?

Thread Starter

mishra87

Joined Jan 17, 2016
619
Hi All,

Directly i want to ask my doubts :

1. Is schematic attached is correct ? - this board to communication over 3 meter distance so there is two transceiver is used at both board . One board connection i attached. could any body confirm if it is correct ?

MCU1-> TX1 -> DIN1 -> DOUT1 -> RIN1 -> ROUT1 -> RX2 -> MCU2
MCU1 <-RX1 <- ROUT1 <- RIN1 <- DOUT1<- DIN1 <- TX2 <- MCU2

2. Can i add 100ohm series resistor at MCU end in both lines ?

3. Can i add RC filter after max3232 transceiver i.e. 100 ohm with 100nf for filtering purpose ?

4. Can i put ESD diode after at RS232 end as shown and if yes what is the value.

5. How to interperate voltage level of RS 232 for driver and receiver ?
1579972036152.png

Thanks
 

MaxHeadRoom

Joined Jul 18, 2013
19,685
MAX232 produces a +15 -15 required for RS232.
What are you trying to achieve exactly?
The input and output lines do not need any other components added normally, especially if using the same/similar IC at the other end.
Max.
 

LesJones

Joined Jan 8, 2017
2,437
There are a few problems with your schematic.
1 - You have the TX pins of both ends of the link connected together. ( So both ends are shouting on this line and nothing is listening.)
2 - You have the RX of both ends of the link connected together. (So both ends are listening but there is nothing to put a signal on this line.

3 - The diodes will short half of the signals to ground so instead of the signal switching between about - 10 volts to * 10 volts the signal will now only switch from about - 0.6 volts to +10 volts.

4 - The 100 ohm resistors qnd 100 nF capacitors will attenuate the signal unless you were sending data at at very low baud rate.

Les.
 

Thread Starter

mishra87

Joined Jan 17, 2016
619
MAX232 produces a +15 -15 required for RS232.
What are you trying to achieve exactly?
The input and output lines do not need any other components added normally, especially if using the same/similar IC at the other end.
Max.
Thanks.

Yes,
Two max3232 will be used in two board over some distance
Now how do i connect max with MCU on both board,

Thanks
 

Thread Starter

mishra87

Joined Jan 17, 2016
619
There are a few problems with your schematic.
1 - You have the TX pins of both ends of the link connected together. ( So both ends are shouting on this line and nothing is listening.)
2 - You have the RX of both ends of the link connected together. (So both ends are listening but there is nothing to put a signal on this line.

3 - The diodes will short half of the signals to ground so instead of the signal switching between about - 10 volts to * 10 volts the signal will now only switch from about - 0.6 volts to +10 volts.

4 - The 100 ohm resistors qnd 100 nF capacitors will attenuate the signal unless you were sending data at at very low baud rate.

Les.
Thanks

One MCU + Max3232 in one board
Once MCU + Max3232 on second board

How do i design circuit.
 

MaxHeadRoom

Joined Jul 18, 2013
19,685
What is the MCU?
The likes such as Picmicro have the UART module built in!.
If wanting to send to two stations then something like Modbus protocol can be used to address either slave.
Max.
 

Thread Starter

mishra87

Joined Jan 17, 2016
619
Is pull up or pull down required at MCU side in MAX3232 transceiver ?
Is 100 ohm series resistor worth connecting at MCU side ?
 

LesJones

Joined Jan 8, 2017
2,437
What is the problem you are trying to solve by adding components that themselves will cause problems ? If you are having problems caused by noise on between the grounds at both ends of the link why not use a 20 mA loop with opto isolators. this would cope with several hundred volts difference between the grounds at each end of the link. An other possible solution would be to use an RF link using HC-12 (Or similar.) modules each end of the link. If you explain FULLY what you are trying to do there is a much better chance of us solving your problem rather than just telling us about the ways that you think will solve the problem.

Les.
 
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