RS-232 Transceiver PCB Issue - Page 1
Forum section: electronics / projects

author: obsoletepower
author_rank: Contributor
timestamp: November 27, 2023, 03:21:41 am
content: Hello all,I am hoping for some help with my project. I want to connect a 35mm film camera to my computer to access settings and data on the camera. The camera comm protocol is RS-232. So I put together a simple PCB based on the MAX202E IC to interface with my PC (see schematic).I am able to successfully read settings from the camera but I have to attempt multiple times before I get a successful connection and even then I cannot download any data because even if after multiple attempts it finally starts downloading data, it almost immediately gives an error.I have tried different cables, different computers and baud rates but nothing seems to change the behaviour. I have read the data sheet for the MAX202E multiple times but I cannot seem to find anything that can shed some light on the issue.On the schematic, the left DB9 connector is the input from the camera and right DB9 connector is the output to the PC. The camera provides 6V regulated that powers the IC and two ground pins.Any help will be greatly appreciated!!

author: boB
author_rank: Frequent Contributor
timestamp: November 27, 2023, 03:29:53 am
content: Yeah, looks like it "should" work, huh ?I'd put a scope on the signal and see if there is anything obvious.Like low voltage or rounded edges and is the RX going to see near proper logic levels ?How far is the RS232 wire running ? What is the baud rate ?

author: obsoletepower
author_rank: Contributor
timestamp: November 27, 2023, 03:58:57 am
content: Quote from: boB on November 27, 2023, 03:29:53 amThank you for the suggestions! I am going to probe it tomorrow and see if I find anything obvious.I have the Baud rate at 9600 and the RS232 wire is about 3 feet.

author: AndersJ
author_rank: Frequent Contributor
timestamp: November 27, 2023, 02:48:45 pm
content: If the camera has RS232, despite the weird pinout,and your PC also has a RS-232 COM port,then you do not need the MAX202.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: November 27, 2023, 04:27:52 pm
content: Without knowing the model, I'd look into the weirder side of serial comms, the various handshake settings. Maybe you need to connect the RTS CTS lines ?? Or enable or disable xon xoff?

author: Doctorandus_P
author_rank: Super Contributor
timestamp: November 27, 2023, 04:56:54 pm
content: I fully agree with Bob. Measure signal ingerity with an oscilloscope if you can.Another common cause is bad quality connections. For example a bad connector, solder joint or damaged wiring. Wiggle things around a bit during measurements to see if weird things happen with the signals.

author: H.O
author_rank: Frequent Contributor
timestamp: November 27, 2023, 06:16:56 pm
content: Several good points made already, here's another...I see 6V as Vcc on the schematic and I reckon that it's the camera that outputs it. Have you measured it and what voltage is it in reality? The datasheet I'm looking out indicates that 6V is outside of the normal operating condition (which for a MAX202E is 4.5-5.5V).Referenced datasheet:https://www.analog.com/media/en/technical-documentation/data-sheets/max202e-max241e.pdf

author: obsoletepower
author_rank: Contributor
timestamp: November 28, 2023, 08:40:16 pm
content: Thanks everybody for the suggestions. I will investigate further when I have some time this weekend.