I have a small project that is using the following:
Nano v3
433 Mhz Receiver
2 x RS232-TTL modules.
The project works fine but for the following:
When the nano device is unplugged from the USB port and then plugged back in then there is live serial data connection on the RS232 module Windows says that the USB device has malfunctioned.
The module powered up fine if there is no live serial data to the RS232 module.
When the nano has no power to it and hence there is no power to VSS on the RS232 Module but there is live data on the serial port the little power led flickers all the time.
It is like the RS232 power is powering the module.
There are only 4 connections on the RS232 Module - VCC/GND/TX/RX
Basically the device receives data from the RS232 Port (IN) and based on a button click on a 433Mhz receiver it will then adjust the output stream to the RS232 Port (OUT) otherwise it just passes the received data to the transmit on the RS232Port (OUT).
The problem is that when the device is not powered up the RS232 modules are showing a flickering power led. I did not put the led on the diagram.
This causes the USB on the nano to malfunction and windows will not detect it. Removing the IN serial resolves the problem but this is not a solution.
The problem is that the RS232 TTL Module is becoming live when there is a valid RS232 Signal but no power is applied to the VCC pin on the module.
Nano uses tx and rx to talk to usb. If you have rs232 connected to rx tx then is logical that usb doesnt work as expected. Do you need usb for the project, or just for programing sake? You can disconnect the modules, upload sketch, disconnect usb, power nano externally and connect modules.
The USB malfunctions may be due to the large capacitors on the RS232 boards or the amount of current draw by the boards exceeding 100mA at USB insertion. Do you have a second arduino? Use the second arduino to power your RS232 modules and only connect your nano to talk to the modules. Unplug and plug nano when there is live data and see if you still have this problem. There are some solutions to this problem but give it a test first.
Read Reply#3 and Reply#4.
The RS232 modules use the MAX232 chip.
They work fine when used as intended. But as already pointed out , you cannot use them with the Tx & Rx pins interfaced to the Nanos Tx & Rx because those are connected to the USB serial TTL pins. You have to use Software Serial. I discovered this when I first tried to use one of those with my UNO. The problem results from having a THREESOME. There should only be TWO parties involved in a serial TTL interface.
raschemmel:
Read Reply#3 and Reply#4.
The RS232 modules use the MAX232 chip.
They work fine when used as intended. But as already pointed out , you cannot use them with the Tx & Rx pins interfaced to the Nanos Tx & Rx because those are connected to the USB serial TTL pins. You have to use Software Serial. I discovered this when I first tried to use one of those with my UNO. The problem results from having a THREESOME. There should only be TWO parties involved in a serial TTL interface.
As I said previously they are connected to pins 10 & 11 - nothing to do with the hardware serial on the NANO.
Maybe if you posted a schematic of your setup this confusion would not happen. As I have said many times here a physical layout diagram is useless for understanding circuits.
Grumpy_Mike:
Maybe if you posted a schematic of your setup this confusion would not happen. As I have said many times here a physical layout diagram is useless for understanding circuits.
If only OP had exported the fritzing in a larger size, the pin numbers would have been readable and considered as a schematic/connection diagram.
liudr:
If only OP had exported the fritzing in a larger size, the pin numbers would have been readable and considered as a schematic/connection diagram.
