 Digikey and Adafruit bring you this week's Ion and PI is from Allegro Lady Aida. What is this week's new product introduction? Okay that's just cool. I like it when there's new companies. I don't think we've done the Allegro chip yet but I like Allegro and American company I think and they've got a cool logo. They're all logo I thought was awesome really cool but this one again I like that you know that the die chip didn't get the rainbow thing still going on that's cool. So Allegro is known for doing magnetic sensors and they also have some motor controllers and stuff they do robotics and current sensing they're very specialized and they haven't been purchased by Maxime I think so this is a great time to take a look at their new sensor the ACS 37002 so I'm just going to call it the ACS 37 because it's a long number and this is a new generation of isolated current sensor this is current sensors actually taking good advice from the medical community and staying isolated from others like their circuits this is an isolated current sensor. So how do we normally measure current? Well this is like an old project I did and a common way to measure current is you have a very small resistor and it's either on the low side it's between the device you're measuring the load up or the draw of and ground and then you have an op amp you see here in the center an op amp and it has like a high gain maybe like a hundred or a thousand and then after you amplify that you measure the voltage and then you kind of divide by the gain and it tells you and the resistor and it tells you the current. Okay well you can also you know do high side low side is kind of annoying because your ground kind of ends up you have two grounds you have the real ground and then the fake ground so there's also high side sensing and it's kind of like this but the other way that resistors on the top of the power supply but this also has some issues one the voltage that you're measuring on the power might be much higher than the voltage of your op amp or your circuit like you might be measuring a 12 volt battery or a solar panel but your circuit is running at three or five volts so you can get a custom chip and some of these have you know they do the gain and they can have high voltages and so you can do higher low side sensing but either way your measuring circuit is referenced against what you're measuring the load of it's the part of the same circuit the ground is the ground on both sides whether it's high or low side sensing and there are a lot of situations where you want total isolation you don't want any connection at all between what you're measuring and the measurement circuit this could be because you have high voltages you have AC you have you know there's you want to reduce noise that may couple across the two circuits a lot of reasons why you want to have isolated current measurement so these this series of sensors from Allegra what they use is instead of having a resistor where the current goes across the resistor and you measure the voltage differential it actually measures the magnetic field generated from current passing through a conductor now you may remember this from your E&M class you know as as current passes through right hand rule you have a magnetic field that is generated and in this case you just see here a hall effect sensor demonstrating that it can measure the output and with careful calibration you can take that magnetic flux and back correlate it to how much current you have to do a lot of calibration you have to make sure that your hall effect sensors the same every time and that the resistor is very precise but it is possibly a very good quality current sensing so you may be familiar with an earlier Allegra chip the ACS 712s was a very popular chip this could measure under 50 amps it had about 4% error it had high bandwidth and it basically you'd have on one side you have you can see the thick traces are the two traces that are in line with your circuit now it does have to be in series with the circuit but you can see it's on one half of the chip and it could be high side low side middle it can be anywhere you want because again it's completely isolated electrically and the output is a voltage in the voltage you know it's either zero with the middle and it goes above and below or it's ratio metric or it could be from zero to above if it's only positive voltages either way this is the old generation and so if you're familiar with that chip this is the next generation this is a really cool image you can see here there's the Hall effect sensor in the center and you see how there's like four pins for each connection so you have like a lot of current passed through and the there's a basically a resistance it's very low because like 0.4 oh sorry 0.4 milli ohms so it shouldn't affect your current draw your voltage across the chip as much and then there's an electrical isolation using a plastic layer between the Hall effect sensor and the magnetic plate it's sorry the the plate that it's measuring the electrical current coming through what's nice about the chip is it's a much higher quality chip than the ACS-712 the inline resistor is much lower I actually wrote that down so hold on so one thing is you can measure much higher currents so it can go up to 66 amps which is kind of nice the resistor is much lower I think it's about one half the linearity is a lot better it's about twice as good there's you know a lot of things that are improved with the circuit since there's a next generation so if you've been looking at the ACS-712 I recommend looking at this chip as an upgrade another nice thing is there's a gain selection so there's all these extra pins so they added gain selection so there's you can see here on the top right you can set the gain by there's two pins and from zero zero to one one you can have different gains from 30 millivolts per amp up to 60 millivolts per amp so you can tune it to get you know the best performance because you want to have your current range be very close to but slightly larger than what you're actually expecting to measure there's also interrupt pins and some other good stuff this chip does come in a wide variety one thing I noticed is that there's kind of like a high there's like a low noise version and then there's also like a high range version so you want to take a look it's like if you want different ranges of different sensitivities nothing unlike the ACS-712 this comes in a nominal 3.3 volt voltage for analogs and digital converters are just really nice because most chips these days are 3.3 volt if you do though you have to pick the 3.3 volt version so there's like a 5 volt the 3 volt just make sure you pick the right one look at the selection guide here shown from the data sheet you know basically decide is it going to be you know bidirectional current great there's a couple that do bidirectional what is your logic level voltage and then do you want higher precision lower noise and then you can kind of pare down to figure out the exact model you want to get but you can pick these up a digikey they're in stock now and I even picked up some myself so I thought I'd show on the overhead and then we could watch a video that's again it's for the older ACS-712 but the same kind of concept I normally read the product ID number but this one's super long but it's digikey.com slash short slash ZRB8P4 but you can also just search for it and let's check it out on the overhead and then we'll play maybe a little video from them. Yes so let me lock on okay so this is how the chip comes so it comes in at kind of a standard wide SOIC and it's of course going to be hard to peel it off so this is the chip and then you know one half I think it's on this side four pins are the you know the one side your connector four pins are the other side I know it's so it's so small yeah one on the I think that's on the right side and then so yeah four lower pins connect to one and four hot other pins go to the other end so that's in series and then you've got power ground two gain selects and the interrupt output this is too close yeah so it's nice and big and easy to use you can even prototype with it and very high current range and again you can use it I think the isolation is like 4.8 kilovolts or something and it's great for AC or DC mention that it can do up to 40 400 kilo 400 Hertz AC which is one of the things that like a current transformer won't do as nicely for you so I think solar panels use high voltage and high frequency AC it's one of the purposes of this is to help measure solar panel output all right and let's listen from the source got a little bit of video current flows in and out of the package it travels in the package through a three-quarter loop inside the package and then back out again this current flow generates a magnetic field around the loop that is proportional to the magnitude of the current flowing in the conductor the resistance of these Allegro sensor ICs is only about 1 milli ohm and therefore the power loss is extremely low making them highly efficient in sensing currents as high as 50 amps continuous current an Allegro Hall of X sensor IC is integrated into the package and it senses the magnetic field generated by the current flowing in the conductor the Hall transducer converts the magnetic field into a voltage flip chip technology allows the Hall transducer to be placed over the portion of the loop where the magnetic field is strongest the flip chip technology also allows for the connection of the signal leads of the IC to the package leads on the other side of the package this also provides the high isolation of these surface mount current sensor IC packages while the Hall sensor IC is in close proximity to the current loop there is an insulating layer of plastic between the two as can be seen in this cross-section this insulating layer provides high voltage isolation and allows Allegro current sensor ICs to be used in AC line tied applications and once again get that on digikey.com and that is