Hello all,
as i’ve measured the outgoing voltage on rs232-port on a Routerboard does have ~ -6 Volt on PIN-3.
Is it possible to increase this to (-/+) 7-8 Volt. I need this higher voltage for an adapter to connect to a serial-modbus interface, that starts to run with its opto-coppling-interface at 7 Volt. I want to load statistical data from a autonomic solar-power-system and to process this data via virtual-serial-interface on a webserver.
Does anyone have any idea how to do this?
Regards
The RS232 standards specify a voltage between +3 and +15v for the space (low) state, -3 and -15v for the mark (high) state. Additionally inputs have to withstand +/- 25v, and outputs being shorted to ground.
So the Routerboard output is within specifications, it is likely that your Modbus interface is incorrectly abusing the standard. If you can’t replace the Modbus interface then an RS232 booster/repeater with a more capable output, or if the Routerboard has a USB interface a USB-to-serial device could be used.
Question: Is it possible to increase this to (-/+) 7-8 Volt.
Answers:
As already stated by tdw , the voltage you are measuring is within spec.
If you know something about digital electronics, it’s possible to build a small voltage converter.
You will need a power supply that supplies the voltages you want ( in your case +12 and -12 volts ). It possible to use two 12-Volt wall transformers. One for the +12 and a second power supply for the -12 volts.
You also need a Motorola MC1488 IC chip ( Quad Line Receiver / RS-232 in ) and a Motorola MC 1489 IC chip ( Quad Line Driver / RS-232 out ). ( The 1489 IC is designed to receive RS-232 and the 1488 is designed to transmit RS-232.
Both IC chips can use a -12 volt pin and a +12 volt pin.
Then you connect your low-voltage RS-232 TX wire to pin 4 of the 1489 and pin 3 of the 1489 to pin 2 of the 1488. Then Pin 3 of the 1488 is the RS-232 output at +/- 12 volts.
I am going from memory , you may need to double check the pinouts and check to see if I missed anything.
Total estimated cost for parts , under 12 bucks ( possibly 3 dollars ).
FYI - back in the late 70s and the 80s, I used to design and build RS-232 test products - almost 40 years ago …
In 1983, I designed a RS-232 hub ( similar to a ethernet switch/hub ) we used them for ATM machines and teller terminals at City National Bank ( long before ethernet or IP or IPX was invented ).