Parallel port and Visual Basic?

Run PowerBasic under DOS. No problems!

John

start and

catch these

Basic

parallel port

parallel

newsgroups, but

I agree with Mr. Larkin. As a WAG, assume the Pinewood Derby cars are going at least 10 mph at the end of the track. That means about 15 feet per second, which means 20 car lengths per second (8" car length). Winning by 1/10th of a car length (you can easily see that yourself) would mean you need much better than 5ms. latency. I would think

0.5ms. latency would be barely adequate for this job. Sorry, but that isn't going to happen with VB. No way.

Power BASIC is ideal for this job.

If the OP wants to hijack the PC system timer for greater accuracy instead of relying on a calibrated timing loop, here's a C program listing that could easily be ported to Power BASIC:

For newbies or hobbyists using the parallel port for real-world I/O, the ideal source is Jan Axelson's "Parallel Port Complete", which is available from many sources, including the Lakeview Research website:

The links on this webpage alone should be enough for the OP to figure out how to do parallel port hardware in Power BASIC, QB, C, or any DOS language he knows already. But the book and CD are a great investment, and will allow the OP to learn more and get up to speed quickly.

The book also has the drivers he would need to do this in VB, as well as lots of sample code. However, it probably won't work well, because no VB program will be able to devote exclusive attention to the port. Windows just has so many other fascinating things to do that are _so_ important ;-) He'll probably only get ballpark 10 ms. or 20ms. latency at best with VB, which isn't good enough.

Thanks, Chris

I am in the process of building a circuit that will monitor the start and finish times for pine box derby cars. I would like to be able to catch these events by feeding signals, through the parallel port, to a Visual Basic program. I was thinking of using the eight data pins from the parallel port to monitor eight lanes.

The electronics are good to go. My problem is with Visual Basic.

Does anyone know how to access and capture bit patterns from the parallel port using Visual Basic?

Steve

PS...I have asked this same question in several programming newsgroups, but I have not recieved any responses.

You may want to get the lpt-vb.zip file from the below site. It has some vb source code for the parallel port. If you are using NT/2K/XP, you may also need an application called userport (google for userport.zip) to get direct hardware access to the parallel port.

In addition to what others have said, note that the default port configuration only has 5 input lines, one of which is inverted, and they are on the Status port. If you want to read 8 inputs at once on the Data port (which defaults to output-only), you'll need to set a bidirectional mode. Alternatively, you could use 2 reads, of the Status and Control ports, and get perhaps as many as 10 lines with some bit-fiddling.

I agree that Windows is unlikely to work for this, unless you are handy with Ring 0 driver development. I'd use real-mode DOS (*not* a "DOS prompt" from Windows), which requires Win9x or earlier. You will be able to get response times in the 10 microsecond range. You will have to read the port(s) in a tight loop if you want to get individual times, although if you just want to find the winner you could OR all lines together to trigger an interrupt (the printer interrupt, typically IRQ 7) when the first one crosses, and then read the port to figure out which one it was.

You might be able to do this as a TSR, probably in assembly, and have it post the results somewhere that your Basic code could read it at its own pace. But you can't install TSRs under Windows, so that leaves out Visual Basic. Sorry! Might want to look into old QuickBasic for DOS.

Best regards,

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

I just had a wild idea that should do the trick in any version of Windows, using VB or almost any language: Use the sound card! You can set the sample rate to 44100 or 48000 Hz to get better than 23 usec resolution. There is good language and API support for recording. All you need is a way to encode the

8 channels onto one (or 2) analog input. The solution is to make a really simple D/A converter. I'd recommend an R-2R ladder type, since they are less sensitive to resistor tolerance than a weighted resistor scheme. Now each channel will produce it's own unique level, and each observed level will be due to one and only one unique combination of inputs.

The sound card is AC coupled, so this only works for a situation like yours, where the cars pass a detector and produce a pulse that lasts a short time. Sound cards typically go down to at least 20 Hz, so the waveform should be pretty flat on top for the short duration of a car's passage.

If you have only one car pass it's detector at a time for a "clear winner" situation, then you just get a pulse whose height encodes which track it is. The duration tells you the speed. If you get more than one car at a time, you will have to decode the amplitude waveform, but I think this will be pretty straightforward. (Certainly compared to writing ring 0 drivers to use the parallel port!) And note that this is "real-time" performance under Windows, which is nearly impossible to get any other way, since the sound card is doing all the heavy lifting.

Note that you will need to take care that you set the mixer controls to the same settings each time. Windows doesn't make this easy; you either get uncalibrated sliders in the standard mixer, or you have to confront the Mixer API... the most abominable interface in the whole Windows menagerie. So you might want to come up with a simple calibration scheme, where you just run one car down the MSB lane and normalize to the recovered pulse height.

Best regards,

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

you can use the dll file inpout32.dll from