Max232 to convert non-standard rs232 signal to TTL?

The signal is inverted, right, meaning that the logic follows RS232 (high voltage=logic low).
The sensor's description says you can directly connect ths signal to an RS232 receiver's input and hope for correct TTL logic output (even though the RS232 signal is non-standard).
Or you can use a standard TTL (or CMOS) inverter to "receive" the RS232 signal.

From an electronic point of view you can connect the pseudo-RS232 signal directly to an arduino's TTL port without risking destruction, but due to the inverted logic level the UART on the µC will not be able to decipher the data.

If you don't want to add hardware to the arduino, you could also try:
- feed the pseudo RS232 signal to an input pin of the arduino that can issue an interrupt when the state changes.
- In the interrupt routine, read the logic level from the pin, invert it and send it as output to another pin of the arduino. Voilá, a software inverter is created..
- wire this output pin to the input of the UART.
This will work only for comparatively low baudrates due to the jitter introduced by the "software inverter". 9600 bd might be feasible.



Side answer: get a PCB (perfboard, protoboard...). Or just glue it upside down onto any available space (e.g. back of anther IC), Use magnet wire for the wiring and solder the wires and any components (e.g. capacitors) freely to the pins.