I've just recycled an LCF-23T CMOS camera (http://www.thaieasyelec.net/index.php/Sensors/Light-/-Imaging/4dsystem-JPEG-Color-Camera-UART-TTL-Interface-OV528-Chip/p_177.html) that the vendor describes as TTL-level UART camera. I don't know the original implementation, the mainboard it was connected to was missing.
My camera looks exactly like one from the link above, but because it has an MAX3232 (TSSOP-16) installed (bottom-right corner) I started wondering if the terminals are still TTL-level or maybe RS232-level?
There is a second model, that looks exaclty the same: http://lianchao.sell.everychina.com/p-90650675/showimage.html but doesn't have the MAX3232 installed yet still described as TTL-level. Something is wrong then.
I checked the terminals connections on my model and they are following (looking from left to right): Vcc, GND, TX and RX. TX and RX are connected to MAX3232's T2OUT and R2IN respectively so I'd say they are RS232-level.
In that case (provided the PCB is the same for 1st and 2nd model) how is that possible that without populating the MAX3232 the interface is TTL-level? I'd expect some of the terminals were connected to RxOUT and TxIN but they are not.
How can I check the signal levels with only multimeter and not damaging the camera?
If I connect it to RS232 and it is TTL-level it will be damaged, if connected to TTL-level device and it's RS232 it can damage the TTL device or at least won't work.