 the great search right to buy a friendage key lady user powers of engineering every single week do help you find the thing you need lady to what is on the Great search this week. Okay, so this week Because I am working on my NA you 702 tester. Maybe you're the overhead. I'll show that again So the any 70802 it's a 24-bit ABC It's got differential inputs, which you need because it's good for measuring Wheatstone bridge type devices like strain gauges There's other there's a lot of other sensors that are our Wheatstone bridges that are very sensitive although strain gauges are kind of the most popular and The so the NA you 70802 I ordered A few months ago and it finally came in so I'll be able to make hours But the thing is it if somebody else was okay. I want to make my own You know Wheatstone bridge amplifier. I'd be like, hey, you can't get any because if you search on digit key This isn't gonna come into stock till like early 2023 So I thought for the great search what we could do is I could find you an alternative because I got mine But maybe you want yours and you don't want to wait eight ten months until these chips come back in the stock So let's identify another good Wheatstone bridge amplifier. So I'm gonna look for something. That's 24-bit I use I squared C but maybe SPI is also good. So we'll look for both Um, and we want something that has differential inputs and something which is pretty common that you see So I'm not too worried about it is in stock and it has a programmable game. So let's go to the computer So one of the things that's kind of nice about The NA 70802 is it has you know, the the the rate isn't very high The reason it's inexpensive is it's like, you know, you pretty much run it at 80 samples per second And that's great for just measuring weight. It's not good for measuring Um, you know a lot of like EMG type sensors or whatever anything that's precision that you need fast responses on But for weight weight doesn't change that much, you know, you put something on the scale and then You know, you're okay waiting two seconds until you get a stable measurement But one thing that is really nice is it has this built-in gain So programmable gain amplifiers is is quite nice as is the analog section inside That'll let you adjust the gain higher gain usually means more noise. And so you want to have like a balance But you know the higher the gain also the smallest signals you can read So, you know, you want a balance of like being able to read small signals But also not, you know blowing out your range because if there's A lot of movement in the signal Your your pga is going to overflow your 24 bit reading So you can dynamically change it which is quite nice. Uh, so Let's go to digiki and so the chip i'm using is the nau 7802, which is This chip, um, the dip is in stock. So if you happen to be okay with that, uh, they do have lots, which is wonderful Um, but the chip that i've been using is the smt the so i see version Um, and then if you look, uh, you know, it's not going to be in stock for a bit and it could be even longer So let's um Let's find a good alternative Um, so i'm just going to look for 24 bits I'm not going to select the other uh inputs I will only go with one adc because you're always going to pay for more adc's and you definitely need one Um, and they definitely want to be surface mount, but everything else is kind of like up for grabs again I don't really care If the voltage range is you know 3.3 volts and also features, you know, there's always like a range of features possible Um And the configuration also might be different also i'll show you the differential and single-ended like pretty much any adc Once you get to like 16 bit they're all going to have differential inputs It's it's actually quite rare to not see a differential input on An adc once you're paying more than like a couple dollars on it Okay, so let's go for active and again, we're we're gonna we're gonna later filter for in stock Um, but i'm going to exclude marketplace. So we only see we don't see like the reseller Uh once okay, um Just samples per second against we don't we don't really care about the samples per second Um input type. I don't actually totally trust this so i'm going to ignore it as well Um, and then what I will do is I'm going to go for the data interface. So Um spi is okay, and I want i squared c i2 s I don't want that's audio input and parallel. I don't want An lvds. I don't want so i'm just going to go for spi I don't know what serial is a serial could be your Or it could be spi or it could be i2c And then um, let's search For those and then um, okay, so there's a lot of options, which is good But a lot of them are kind of expensive So i'm going to just sort by price because that's what we we care about and as expected The na u702 are like the cheapest so the ones that we can't get are about like a dollar or two, which is uh Unfortunate because we can't get them But there is this one over here this 56 35 65 from microchip um One thing to notice it has much higher sample rate has 153k, which is great. It still has two inputs It's also differential and seeing on it. However, it's only i squared c Um, one thing that's a little, you know, I was a little at first. I was worried because I was like, oh, this doesn't have Programmable gain. It also has a lower voltage range. It only goes up to 3.3 volts Um, but when I looked at the datasheet because I was like, well, you know, I got a look to to make sure Does it really not have gain? It actually does have programmable gain it has it goes up to 64 it goes up to 64 times gain Whereas the na u702 does 128 64 is still pretty good. Um You know, I think it's probably fine Uh, it has uh, you know external clock selector just like the na u it has differential Inputs like you'd expect there's gain error calibration. So you can do it's like very tiny. It's kind of cute. It's like, hi, I'm just a little I'm just like a little bored here and um, you know, if you search for You know a typical application for a ratio metric a wheat stone bridge Pressure sensors and load cells. It's very common So this is, you know, what it would look like pretty straightforward. You have the Um, like the na u it's kind of nice. It can do the the reference in and out. So you have um, you you know any You know, if you're doing the ratio metric input You want to make sure that your positive input to the wheat stone bridge is exactly the same as your positive reference to the ADC and so any noise gets cancelled out because again, you're only measuring the the difference between Um, the voltage divider between the positive and the negative rail on the bridge here Um, so what's nice is that you've got the reference in plus and the reference in minus and you just make sure they match up And they just need an rc filter. So this is for like, uh, you know rtds for, uh, pressure sensors for Load cells like, you know the before you also use it for other stuff like, um, thermocouple amplifiers and stuff which need precision Differential inputs as well because you're measuring the little micro volt Changes on your k-tech thermocouple. So this chip will do the job quite nicely Uh, it looks like there's a few in that family the 35 6x Um, they're all fairly inexpensive comes with a couple options. Um, and this one at least is in stock. So that's that's great Um, but let's uh, let's also filter for only in stock The other option I found, um, so the that one was spi And you might be like, well, I really don't want spi. I really want i squared c Um, well i squared c is a couple but most of them are not in stock the first one that's in stock. That's i squared c Let's quickly go over here and select i2c Not a lot of things in stock or if you are normally stocking. Um, but this one did come up. This is the abs 12 19 um Which I downloaded the datasheet So this is fairly also, you know, pretty fast. It's a one kill a sample per second um adc This doesn't have as many programmable gains that only goes up to four times gain So, you know, I don't know if you know, it could be good enough for uh, you know, we stone bridge But I think it would be tough without another amplifier um, that said it has four inputs So this is like, you know, I think you could use it with a weedstone bridge, but I think you'd probably want Um, you wouldn't get as much signal. You probably want amplifier Yeah, they don't have a recommendation. So, you know, it's the one that's i squared c But it's not it's not great for that use purpose. However It is i squared c in 24 bits. So depending on what you're using it for, um, You know, if it's if it's not a load cell, it might be okay If you are using a load cell, I would probably and you don't mind going with spi I would say that the mcp 35 6 series is your best bet So you got two options to pick your pick your poison differential options. That's a great church