Using the ACS712 Hall Effect Current Sensor Module (part 1)

this is the ACS 7 1/2 Hall effect based linear current sensor from Allegro Microsystems and in this small outline 8 pin package there are I think three types this is the 5 amp there's also a 20 amp and a 30 amp type and now if you want to buy this chip on eBay just the chip you're looking at about four or five pounds but due to the wonders of Chinese economics if you want it mounted on this board with all the connectors in place you're looking at about 2 pound 50 now one gripe I do have with this type of terminal block is that when you try and turn the screws the whole block twists on the board and that's because there are no locating plastic lugs and it just turns on the the metal work that's underneath but fortunately the supplier of this Court has very kindly not soldered the connector in so I think I'm going to use it like this where I'll just put ring terminals directly onto the holes in the circuit board now my plan is to mount the current sensor sort of here on my solar panel voltage and current test rig the voltage sensor is already mounted there the microcontroller is here with the display and I'm going to use it to measure solar panel voltage and current now the conventional way to measure current and it's used in this cheap nasty multimeter on the tenant range is to measure the voltage across a low value resistor and the resistors here it's this thick piece of copper wire that spans the common connection and the 10 amp socket and the voltage across a thick piece of wire like that with an extreme Nilo resistance is going to be very low so the chip up here will have an amplifier to increase that voltage and make it measurable and the same technique is used with this on this DC power supply you can see there is a low value resistor it's a 0.01 ohms and the current will flow through it the voltage across it will be measured but of course that voltage is very small so here down there there's an op-amp and that scales the voltage up multiplies it up but of course that's subject to interference by noise temperature drift and other problems like that so I now have the Hall effect current sensor attached to my circuit here it is and this module will have solar panel on the left-hand side and a battery on the right-hand side and the current needs to be measured on the high side of the circuit so I don't want to be measuring current in the ground line now this chip works a little bit like an opto isolator in the sense that the current sense element on the left hand side is electrically isolated completely from the measuring device on this right-hand side and you can have something like 1.2 kilovolts between the two sides and the chip will still function completely normally it isn't opto isolation in this case it's magnetic isolation there's a magnetic field surrounding the piece of wire when current flows through here and there's a Hall effect sensor on this side of the chip which detects that current and through a little bit of integral electronics provides a signal on these pins that is between 0 and 5 volts and you can ground or have to ground this ground pin here to system ground and that's perfectly OK it doesn't interfere with the high side measurement of current right so I've put 5 volts onto the VCC and ground pins on the module there and I've got the voltmeter connected to the center pin measuring volts coming out of the sensor now the way this works is that it's bi-directional so currently there's no current flowing through the yellow and red wires so the voltage coming out sits at the midpoint between VCC at 5 volts and ground at 0 so you can see that it's 2 and a half volts now without putting a current through it I'm just going to disturb the magnetic field using a magnet attached to a screwdriver and you can see that if I get the magnet really near the chip the voltage swings right down almost to zero I spin the magnet round and bring it in again then the voltage shoots up so you do have to be a little bit careful of magnetic fields because they will disturb the operation of this device and now I've got some current flowing through the current sensor it's a bit of a lash up it's just a 12 volt bulb and I've got 12 volts coming round the circuit and it's reading 2.1 9 volts now that doesn't tell you anything but you have to know that this current sensor has a scale of 185 million bucks per amp so all you need to do is take the original 2.5 volts subtract the 2 point 1 9 volts that is reading now and then divide by point 1 8 5 which will finally give us amps so there are 1 point 6 7 amps flowing through this circuit now that might seem an extremely difficult way to read current and of course it is by just putting a DVM on the output of the current sensor module but of course this sense module is designed to work with a micro computer microcontroller like the Arduino and so in part 2 of this video when I get my display I don't have it at the moment I'll put the Arduino on this and then that will be able to do all the necessary calculations to produce a current display in amps on the liquid crystal display

Channel: Julian Ilett

Views: 353,269

Keywords: ACS712, current, voltage, power, hall effect, arduino

Id: UF5jrnXvTlM

Length: 6min 44sec (404 seconds)

Published: Sun Apr 28 2013