PaulS:
Is the device really an RS232 device? The Arduino can not handle an RS232 device directly. The serial signals are the wrong voltage and are inverted. You need a MAX232 chip between the Arduino and any RS232 device to handle the voltage differences.
Thanks Paul.
Yeah, I was thinking maybe I should use a converter between this two devices as well.
I did some research about the TTL voltage and RS232 voltage, and I noticed that the output voltage coming from RS232 would be as high as 25V. But when I used the voltage meter to measure the output port of the light meter, the voltage value was only 5V.
So I'm confused. The cable they provide is a RS232 cable, but the output doesn't reach the 25V.
Do I still need the MAX232 chip in this condition?