[RESOLVED] Monitor Voltages Using RS232

[dw85745]

Out of personal necessity I need to monitor some automobile sensor output
-- intermittent problem -- and datalog it. Have both a VB6 Oscilloscope software as well as some API RS232 port monitoring software.

Not being an electrical engineer - thought why not use the RS232 to do this.

However, a major concern is the voltages that any given sensor will put out in relationship to what the RS232 / computer can handle -- don't want to kill my computer.

So my questions are:

1) What pins of the RS232 port are the best for monitoring input?
For example if you have an oscilloscope (software) and it requires
two leads for input -- one should be ground and the other the signal
what RS232 pins should you use?

2) Can you hook up a sensor output directly to the RS232 port pins?
For example if the sensor puts out a voltage ranging from 0 to 5 volts, can this be hooked up directly to the RS232 port or will it kill it and the computer.

3) If NOT a direct hookup, how do you reduce the voltages (e.g resistor) to an acceptable level for the RS232 to handle?

[Doogle]

I don't think that RS232 is what you need. It expects signals to be 1 or 0 (-12Volts or +12 Volts with respect to ground) with bits arrving in a fixed period of time.

All software oscilloscopes I've seen take their input from the Microphone or Line Input sockets.

[dw85745]

Doogle:

Thanks for responding.
Just reading the RS232 specs (wikepedia).

The RS-232 standard defines the voltage levels that correspond to logical one and logical zero levels for the data transmission and the control signal lines. Valid signals are plus or minus 3 to 15 volts; the ±3 V range near zero volts is not a valid RS-232 level. The standard specifies a maximum open-circuit voltage of 25 volts: signal levels of ±5 V, ±10 V, ±12 V, and ±15 V are all commonly seen depending on the power supplies available within a device. RS-232 drivers and receivers must be able to withstand indefinite short circuit to ground or to any voltage level up to ±25 volts.

So if I understand correctly, the RS232 takes any negative voltage and makes it a 0 and any positive voltage and
makes it a one -- OR -- do the voltages have to be mirror (e.g. +/- the same value) to each other?
If this is the case, I can see where trying to put out a graph where sensor voltages range from 0 to +5
may be difficult since the RS232 would only interrupt it was receiving a string of 1's based on the fact that 0 to 3 are not valid (per spec),
so only 4 and 5 volts would be interrupted as ones.

So how does one go about measuring a range of voltages using the computer?

[dilettante]

You might consider some sort of USB Voltmeter for this.

[dw85745]

dilettante: Thanks

Looks like I need some type of interface hardware anyway I go.
Had hoped to learn some new programming by coding for one of the PC connectors.

[DickGrier]

I have information on this under PC Data Acquistion on my website (www.hardandsoftware.net). The least expensive serial ADC that I have experienced is http://www.dlpdesign.com/usb/io8.shtml (though you also can use a starter kit from DataQ, http://www.dataq.com/data-acquisitio...arter-kits.htm, for the same price, the software interface is more difficult, though not imposible. You also can purchase an Ardunio board for about the same prices, and write code that received measurement from that board -- this will require more code than either of the previous suggestion.

There also are much more expensive variations. I don't make any money from the information on my site, so I have no axe to grind.

Dick

[dw85745]

Mr. Grier thanks for responding.

Took a quick look see at your site so I could post and thank you for the link.
I did find that one of your links is broken

Open Data Acquisition Association

Am in the crawling stage, so not real sure of the questions I should be asking.

Above are a few questions that I thought were valid as a starter. Any answers for the above?

David

[DickGrier]

See the page link for Serial Port (to the left on the introductory PC Data Acquisition page).

Actual code depends on the device you use. I have several different examples in my book, but there are are a number of devices available that I have not used.

I'll check the broken link.

Dick

[dw85745]

I'll consider this resolved for now. Have some reading to do.