Sat Mar 06, 2021 1:27 am
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 ).