RS232 Common Problem / Solution?
Eric R
Posts: 225
At work today I had an issue with a RS232 divice where I felt certain that the equipment was not at fault but rather a poor / incorrect data string. The easy way out of this is to grab the $2000 laptop and haul it out to the cold, wet and nasty production floor, fire up hyperterm and see whats going on.·Not exactly what I want to do with a laptop but I wouldn't mind taking a stamp out there.·
Since all the equipment is either 9600 or 19200 N,8,1·I plan to look into the use of a stamp and a simple LCD display that would act much like a little dumb terminal (wyse terminal). Anyone done this? Just thinking out loud at this point but want to give it a shot. Maybe a simple toggle switch for the baude selection·and a momentary to clear the screen. Just need to see valid·or scrambled data.
I don't think you can spy on RS232 inline (like a 3-way tag team) without causing errors correct? Would a couple of diodes correct this condition? Either way, a direct 232 connection will work but a inline connection would likely be better and more usefull·in the long run.
We also use a number of serial printers so I though it might be nice to store·a little test string that would allow non-PC testing of these units. This may be a later project.
As far as power goes, 9V battery?
Anyone care to offer·feature·or construction·recommendations before I set the project in stone?··It doesn't appear to be a tough job, at least with the little thought I have put in it so far, but it might be helpful to others here as well.
Since all the equipment is either 9600 or 19200 N,8,1·I plan to look into the use of a stamp and a simple LCD display that would act much like a little dumb terminal (wyse terminal). Anyone done this? Just thinking out loud at this point but want to give it a shot. Maybe a simple toggle switch for the baude selection·and a momentary to clear the screen. Just need to see valid·or scrambled data.
I don't think you can spy on RS232 inline (like a 3-way tag team) without causing errors correct? Would a couple of diodes correct this condition? Either way, a direct 232 connection will work but a inline connection would likely be better and more usefull·in the long run.
We also use a number of serial printers so I though it might be nice to store·a little test string that would allow non-PC testing of these units. This may be a later project.
As far as power goes, 9V battery?
Anyone care to offer·feature·or construction·recommendations before I set the project in stone?··It doesn't appear to be a tough job, at least with the little thought I have put in it so far, but it might be helpful to others here as well.
Comments
Get one of those RS232 led indicators that show activity via leds, tap into led trace to capture signal, you could do same type of thing with opto-isolators.
They also make three port inline rs232jack/boxes, the 3rd line is for monitoring/capture...
Check this site www.aggsoft.com/rs232-pinout-cable/serial-port-monitor-cable.htm
Or this Google search www.google.com/search?hl=en&q=rs232+monitor&btnG=Google+Search
Bob N9LVU
Post Edited (Robert Kubichek) : 11/10/2005 11:17:52 PM GMT
http://databoy.netfirms.com
Not to sell BS2 short, but I love my DataBoy.· It's "transparent" in circuit.· Those LED gizmos, which can be valuable to check "viability" of connectivity (i.e. Well, it looks like it SHOULD work), tend to load down the drivers and thereby muddy the water.· And·the DataBoy·has a good deal more memory / capture.
I think you can "spy" on the RS-232 levels, I'm not certain in TTL levels, but I do know that you can with true RS-232 levels, (I would suspect so with ttl levels) I know that I have a device that I created that basically you plug the db-9 into it from the device then plug it into the computer port and it has a set of wires coming out of it's side that connect to another computer serial port. So with my second serial port I could see what my first one was doing. this was before I found out how to "spy" on it digitally with a custom VB6 program. [noparse]:)[/noparse]
The dumb terminal seems extremly feasible, especially since I've created the same thing. [noparse];)[/noparse]
My Electronics test bench is about 100 feet away from my computer, so I program it with my computer, then go to the bench to see if it all worked, then I disconnect the computer's serial port and connect a "dumb terminal" to the programming port of the stamp, basically it's a LCD screen with a RS-232 level converter. It's enough to give me information via the "debug" command. My newest "dumb termnial" will have a BS2 in it, and it'll be alot smarter, but that's just on the list of projects to be done at some point... (no time soon....)
It would be REALLY Easy to make the stamp send a serial string to the serial printer....
9V battery is almost ideal.... just make sure you're LCD's "backlight" is off when not in use.... Current consumption can be around 15ma for everything (basic stamp included), but with a backlit screen it jumps to 70-80 ma. (just values off the top of my head, so don't base exclusivly off that.... )
Knight.
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