LabVIEW
Control a serial port pin for a variable DC output.
A typical PC does not have any variable output ports other than the audio jack. You can use the serial port's flow control lines (like DTR/RTS/etc) but those will be on or off. VISA can control these lines as far as I know.
The audio jack is analog, but AFAIK it can't hold a steady DC voltage on it. It's got highpass filters on the output so the best you can do is hold a constant sine wave. You could then rectify and lowpass that signal to get a variable voltage output... but that's a crapload of work that probably won't be the same PC to PC. You can use the built-in "play sound" functions to control the audio jack indirectly. Once you "calibrate" the volume of a sound file (and the PC as a whole...) to a specific voltage level then you could get something kinda repeatable. However, any change to the Windows volume setting would mess things up.
With actual NI DAQ devices costing just $200-$400 (IIRC), I can't imagine you saving any money here.
If you were REALLY budget strapped you could use an Arduino with LYNX to vary the voltage. An Arduino costs like $3 for simple ones. You'd be limited to 3.3 or 5V max but it'd be super simple.
Edit: I just saw your other post where you said you wanted "quick and easy". The answer is a resounding no, you cannot do variable voltage control quickly and easily. A cheap DAQ is the answer, which you can get working in about 15 minutes and have all kinds of control over the output.
If you just need some waveform, any waveform, with little control over the levels, you could use the sound card output. I can't imagine that being useful for much of anything. You'd be limited to something like 1 V as well.
This is not a LabVIEW limitation; it's a PC limitation. It might help if you described what you're actually trying to do.
Hah, I understand that completely 🙂
Purchasing often gets in the way of progress... so good luck with that 🙂
If I were you, I'd push for the DAQ setup. It'll be more versatile, and the next time you need something like that you'll have it. The Arduino will be a much cheaper option in the short term, but if you're working for a big company then the extra time to program it will absolutely be more expensive in the long run.
The only reason I'd suggest something super low cost would be if you're working on some device that'd get resold at the absolute lowest cost possible (think like charitable work for impoverished people, like super low cost microscopes for remote villages or something). For a lab use? Yeah, I recommend DAQ all day long.
@K C wrote:
Now your suggestion. I think it will take some electronics to get this done.. You could use the lines from the serial port to control a DAC IC. But in most case I think it will end up in a PCB full of components to get it done. Cheap (but that was not the problem), but it will take a lot of time.
Creating a PCB full of components is cheap? That doesn't even work if it is just for a hobby project and your time doesn't ''cost" anything. But doing this for something at work where your hours actually cost something? Naah, definitely NOT cheap!
For the price of a cheap USB DAQ device you can't even start to heat up your solder iron (put a little over the top, but only very little, especially if you talk about a multi billion dollar company). 😀
Talk to your manager. Tell him you need this device and if he can get his influence in. Maybe he knows the right people in purchasing, or his manager does. And maybe he whips out his company credit card and simply buys it. 😁
Remember that rules exist to find a way around them. Just stay legal when doing so.
@K C wrote:
I agree it is not cheap, But when you already have the components it only will cost hours and no out-of-pocket money. You would surprised how some companies calculate their cost.
Anyway the hours already spend on this would easily cover the cost of a DAQ, I think.
On the other hand, engineering/technician hours are NOT cheap. The labor you would put into a one-off solution compared to buying something you can reuse?
You know how components or designs are often chosen? Design engineers will set up a meeting, and if the "discussion" goes beyond a certain amount of time, the project manager will instruct them to make a choice NOW, because the engineering hours just spent discussing it cost more than the component/construction of the designed component itself.
Cheapest way would be to use an Arduino's PWM output and a simple circuit like this:
You set the voltage by adjusting the PWM on D5. (or whatever PWM output you use).
