2021.03.04 - Veeder-Root TLS-300 Serial
Got to do something different today, figuring out how to connect over serial to a Fuel Tank Gauge monitor
Intro
So today I got to do something different. A friend of the boss runs a fuel/oil delivery business and was trying to install a remote monitoring system for an existing fuel tank monitor. The fuel tank monitor had a 25-pin serial port on it and he was trying to connect it to the 9-pin serial port on a cellular modem. The company that provided him with the cellular modem I guess just sends along a kit of random serial port adapters/gender changers/null modem adapters and they just have him keep trying random things they get a connection. After a hour of trying random things they gave up finding the right combo and called for help.
Of course I know nothing about this fuel tank monitor, but RS-232 is a pretty basic standard so I figured I'll get to at least talk to a laptop and so from there. Thankfully I have a halfway decent USB to Serial adapter for my laptop, as it's pretty much impossible to find a serial port on any computer now-a-days and most USB to Serial adapters are junk.
Making the Connection
So I got lucky and after a bunch of looking I came across a PDF file on how to connect the TLS-300 to a PC, which was pretty much the golden ticket. It mentioned that on the inside of the TLS-300 there was a group of 4 dip switches and all 4 needed to be set to open. It also explained that the computer should be connected to the "direct" 25-pin serial port on the TLS-300 (there are two of them) with a null modem cable.
The last thing I was missing was how to actaully send it a command from the computer that it would respond to. That the people that provided the cellular modem were able to tell me, so they weren't completely unhelpful. CTRL+A,CTRL+A,100 (and maybe enter after that, I don't remember) and the monitor output a string of numbers. CTRL+A,CTRL+A,200 (and again maybe enter) output a nice human readable output.
Once we got that working the only thing that needed to be changed is the connection to the cellular modem needed to be with a straight through cable instead of null modem. Made that small change and like magic everything worked :) The biggest thing seemed to be those dip switches, in particular switch 3 was set to closed which I think enable some kinda security on the serial port.
-Nick