Hi just a quick two minute Tech tip Video: Have you ever needed to generate a uh, precisely changing voltage in like small little increment steps Like ordinarily okay, you might use your uh, fancy pantsy uh, a modern digital uh, power supply like this, but typically that can I even on a like a duck's guts unit like this rodent. Schwartz Joby Here, you can only do 10 millivolt increments and if you haven't had a need for generating much smaller voltage increments like that and sure, okay, you can put a voltage divider on the output of it and then uh, it gets smaller potential voltage. uh, changes across it and stuff like that, but often, uh, you might be parent using your power supply to power your product. And of course most Labs aren't going to have calibration kit like this with six Decades of voltage adjustment or like a nano volt voltage source like this.

Well, if you don't have any of this and your power supply is being used well, what can you use? Well, you might already have something. Any decently equipped lab these days you should have an arbitrary waveform generator. Doesn't have to be as quite Advanced as this. You can get them quite, uh, cheap.

Whether it's you know, it's the Segland or the Rye goal like this or one are just the cheap. eBay Jobbies. In most cases, you should actually be able to use your arbitrary function generator to generate precisely small stepped voltages. Let's take a look: modern arbitrary waveform generators.

They don't generate the signal analog like old school once did they generate them using typically a 16-bit digital to analog converter, and with that higher resolution analog to digital converter, you can actually get really nice steps on this. A lot of people don't know realize that their arbitrary waveform generator should have a DC option like this. Usually it might be called DC offset or something like that, but they can actually generate a DC voltage on the output, which then can be precisely this one. You might think it goes one millivolt, but we can actually go over and generate 0.1 millivolt steps.

So there's two orders of magnitude better than the best power supply I've got in my lab here. Now it's not magic, of course. There's a couple of issues which I'll go through. The first one is that usually they will have a DC offset.

This one's not bad, so you can see it's a 25 micro volts offset if I set it to zero, but it can be substantially higher than that. This Rigo over here, for example, set it to zero volts. You switch it on and you can see that it's got like a 500 micro volt offset or a 0.5 millivolt offset. So yeah, you can adjust it by uh, 0.1 millivolts.

but you're just going to be aware you're going to have that offset there or you may or may not, depending on you know how decent your signal generator is. But the good news is that you can and actually adjust that by 0.1 millivolt increments. look 0.6 0.7 so you can actually jump up in those 0.1 millivolt increments. So you do have the resolution there to actually do this, but it is going to depend upon the voltage.

uh, span like the total voltage span whether it's plus minus 10 volts output for example, and then the number of bits of your digital analog converter typically 16 bits. The next thing you have to be aware of is that the accuracy of like the voltage source in these things is not great because that's not their main purpose. Their main purpose is to generate waveforms. So your typical accuracy of an OBGYN like this in the order of like one percent something like that.

And when you're trying to make like very small changes like 0.1 millivolts like we're doing here, then you talk. Start talking about the linearity of the digital to analog converter chip used in here and I'll link in the teardown video for this. I Can't remember what one it is, but I'll put it up in the overlay here, but you can can see this signal is pretty good. I can like point one millivolts, it's almost 0.2 Look, I can adjust it 0.1 millivolt steps now.

Unfortunately, once you get to higher voltages like this, you won't be able to do like often. the 0.1 millivolt uh, offset like that? whoop. That was just an error there. actually oops but I can actually go up to plus minus 10 volts on this particular thing.

So plus minus 10 volts with a 16-bit digital analog converter, you get pretty decent DC resolution on these things. It's great. And also, you might have uh, temperature drifts as well because these things don't have the absolute best voltage standards in them. so you know? Yeah, But but if you need to, uh, you don't care about the absolute value? Yeah, I have one percent.

It's good enough for Australia And but you need to adjust and do fine adjust in DC voltages. You can use this signal gen to get an order of magnitude or or two orders of magnitude better than what you can get with a typical DC power supply. And as I said, you're probably using your power supply to power your project anyway. and I know you're going to ask about noise.

So we've got on the scope over here and we can see that we're only talking about you know, 220 microvolts here. But of course your mileage may vary with your particular object. But let me adjust this in one millivolts steps and you can see boom boom boom Boom. We're getting nice one millivolt, but we can actually do 0.1 millivolt steps there and look, you'll see that you can hardly see that change.

but I'm actually adjusting that, you know, doing mine a little changes there. Those bursts are coming like externally. Don't worry, it's not actually coming from the Gen there. There's all sorts of things happening around me.

I've done videos on common mode interference and stuff like that, but there you go. You can actually adjust in like 0.1 millivolt or one millivolt steps. Way better than your power supply, so that could come in real. Handy For you know, all sorts of uh projects that you might need a you know, just a nice and finely adjustable DC voltage the other day.

Downside to this is that your output impedance of your function generator is going to be 50 ohms. So it's like having your nice adjustable 16-bit uh, you know, Precision DC Source but with a 50 Ohm resistor in series. And for those who are wondering, no, it makes no difference if you actually select the output setup here right and we're going to load. If you have the high impedance or the 50 ohm, watch it not change here.

it doesn't change at all. Okay, people think, well, this looks like Chain by a tiny little bit there. So I don't know why it's doing that some internal thing in here, but people think that when you select 50 Ohms output impedance, then there's a relay in there that inserts that 50 ohm on the output. Sorry to tell you, it's always there.

So uh, the high impedance option just changes in software in your RGN what your maximum voltage is. It basically doubles or halves it depending on what uh, setting you're actually got here. So I can show you that right now now we can put High impedance. I'll put my 50 ohm load on there and bingo, it's halved so it makes no difference whether or not you have that 50 ohm setting on.

It's only the maximum voltage that it, well, the actual uh, offset voltage that it actually puts. But when you're doing this, you want higher impedance because you usually put in, you're usually not going to put your nice adjustable little DC voltage into a 50 ohm load. So yeah, make sure it's on high impedance and then this figure will be accurate. Oh, reasonably accurate within the percentage tolerances of your arm Gen.

But anyway, I Hope you found that little tip useful. might have been slightly longer than two minutes and leave a big thumbs up down below if you like two minute Tech Tips like this and hopefully you did you realize something you didn't know before or you'd forgotten or you just didn't think um, that your arm Gen Yeah, even the like, the cheapest ones might use a 14-bit darker or even 16-bit uh converter in them and you can get like really cheap as objects. Um, you know that a complete no name as you can get them on eBay for like 100 bucks or something now and they could actually be useful. It might save you bacon one day.

Um, if you need a nice fine adjustable DC of voltage and as I said, you can actually put it into a voltage divider as well. But just remember that 50 ohm series output resistance in there, you've got to take that into account if you're using an external divider to make sure you get accurate uh, voltages. So if you need to adjust in, you know, 10 microvolt steps or something, you could do that with an external divider. No worries.

Anyway, thoughts and comments down below if you liked it and found it useful. Thumbs up. Catch you next time. All right, Foreign.

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