Hall Effect Devices
Solid State Magnetic Proximity Sensors
All of the devices listed are 3-pin SIP (Single In-Line Packages) leaded types that fit into breadboards. They also come in surface mounted packages so be careful which ones you buy.
The output may be rated in Gauss or Tesla. Most devices have operating points under 200 Gauss or 20 mT. This is about the ability of most typical small magnets at a distance of one inch or less.
1 Gauss = 0.1 mT (Milli-Tesla)
10 G = 1 mT
100 G = 10 mT
1,000 G = 100 mT
10,000 G = 1 Tesla
Positioning of the magnet
Most reed switches found in gaming work with the reed switch parallel to the magnet and parallel to the lines of force around the magnet. Hall Effect Devices work best at the poles of the magnet where the flux lines are more concentrated.
Package types and price
The devices included with this course are the cheapest package types. Similar devices come in different packages. The price varies from under $1.00 to $20.00, or more. They will all work the same way and have the same characteristics.
Exercises
The A1302E was my primary interest. I was looking for an analog output voltage proportional to a magnetic field. To get to know the part I taped the device down (letter side up) to a block of wood with a connector on it leading to a breadboard. Power was derived from the USB port on a local computer so a filter cap was connected close to the device wiring on the breadboard.
Measurement of the output was made with no load resistor and found to be 2.47 Volts with a VCC of 5.05 V. Not exactly 50% of VCC, but as I said, perfection is not found on these parts.
I measured the output just before applying the magnet just to be sure. Then put one end of the magnet close to the sensor, moved it around for a maximum reading and noted the voltage. Since the magnet I had was not marked for North or South I had no idea which way the reading would go. It went positive so the end of the magnet toward the sensor was the South pole. I marked it as such. The output voltage maxed out at 3.41 Volts. The voltage readings stated were as accurate as my meter would measure on a 20 Volt scale. I understood the degree of error involved since the data sheet says the device's output should change 0.0013 (1.3 mV) per Gauss and my meter was only capable of increments of 10 mV with 5% accuracy. 3.41 Volts. Minus 2.47 Volts gives me the change in voltage. Divide that by 0.0013 V and I get a reading of 723 Gauss. (I didn't actually do the math. I built it into an Excel spreadsheet so I wouldn't have to do the math manually at each reading. This also gives me the option of graphing the output.)
Moving the magnet away 1 mm I repeated the process. To get 1 mm I put eleven sheets of 20 pound bond printer paper together in 1" by 2" squares.
Repeating this exercise I made 9 reading at 1 mm intervals, measured the output and graphed the result.
Starting at 9 mm I reversed the process measuring the North pole of the magnet as I got progressively closer, and graphed the result.
I was expecting to find a different result than I got. Other than a slight dog-leg at the closest readings I got a fairly linear rate of change. I was expecting the curve to change at the square of the distance. Not so. I can't explain why.
Moving on to a more powerful magnet I repeated the process.
This time my dog-leg was even more pronounced curve in it. At 1.3 mV per gauss and only 2 Volts of change available I think I exceeded the rated capacity of the device. The data sheet says that exposing the device to greater than the maximum Gauss will not harm the device but will put the output into the non-linear region. I think this is what we see here. I can't expect the output to go rail-to-rail. About 0.5 Volts away from each rail would be normal. This puts the maximum measurable Gauss at about 1,500 Gauss. In this exercise we see the limits of the device being exceeded.
Conclusions...
Use the device well within the rated range to keep the readings linear.
Measure the output by relative change, not absolute voltage.
Don't expect extreme accuracy unless you can measure in 0.0001 Volt resolution.
Applying the lessons from the lab exercises
.
The objective was to use the magnetic flux in a ferrite core (torriod coil) to measure the current in a circuit. At low currents a resistor works fine. You just track the voltage dropped across the resistor to indicate the current. But this was a 5 Amp power supply. The appropriate resistor would have been 600 mV divided by 5 Amp which would require a 0.12 Ohm resistor at greater than 5 Watts. Not having one I started considering options.
So what kind of coil did I need to get a few hundred Gauss at about 5 Amps? After hours of pouring over technical stuff about Ampere-Turns, Inductance, Permeance of Ferrite and realizing I knew nothing about the coils I had I just grabbed a coil that looked like it could handle 5 Amps and tried it. For those who must know the coil has 40 turns of 18 AWG wire around a ferrite core of unknown characteristics.
Cutting a hole in the ferrite just big enough to insert the sensor wasn't a big problem. JB Weld was used to attach the sensor in the hole. Testing the result proved the idea worked. Calibration was a matter of applying a voltage with a load of a known current (1 Amp, 2 Amps and 3 Amps) and measuring the change in output voltage of the A1302E. It works. Not great design or a design of grace and beauty, but it worked.
There are a few advantages of the design over using a resistor and standard circuit. The A1302EUA was available for less than $1.00. The output is fairly linear so I could make the circuit adjustable and have an electronic fuse whose level I could adjust cleanly. We avoid the loss of almost a volt across the resistor. For a low voltage high current power supply this was important. Besides, I really wanted a good reason to play with this new toy. :-).
Exercises for other parts
Other than Hall Effect Sensors that output a voltage proportional to the polarity and strength of a magnetic field there are Hall Effect Switches that simply turn on and off in response to a magnetic field. Some are Unipolar devices that turn on and off at specific strengths of one magnetic polarity (usually +B, or a South facing pole). There are Bipolar devices that turn on when a +B is applied and off when a -B (North pole) is applied. There are also latching devices that turn on and stay on until an opposite pole is experienced. Most families of devices make all these types and more.
Readily available parts at low prices
A1301EUA "01E"
Linear Hall Effect Sensor
VCC = 5 Volts (4.5 to 6.0)
V Out = 2.5 V (VCC/2) at 0 G
V Out increases 2.5 mV per Gauss on +B (South) magnetic field is applied to the lettered face of the device or decreases 2.5 mV per Gauss on -B (North) magnetic field.
I OUT = + or - 1 mA max to stay within accuracy.
Maximum measurable Gauss is just a bit less than 1,000 Gauss.
1 - VCC (5.0 V) @ 10 mA
2 - GND
3 - V OUT
Ratiometric - This term implies that the output will vary in proportion to the VCC voltage. VCC must be regulated and well filtered for proper operation of this device.
The "E" in the part number specifies a temperature range of - 40° C to 85° C. The "UA" specifies the 3 pin SIP leaded package.
The case is too small for the full part number and is just marked "01E".
A1302EUA (1718743, Jameco, $0.96) "02E"
Linear Hall Effect Sensor
VCC = 5 Volts (4.5 to 6.0)
V Out = 2.5 V (VCC/2) at 0 G
V Out increases 1.3 mV per Gauss on +B (South) magnetic field is applied to the lettered face of the device or decreases 1.3 mV per Gauss on -B (North) magnetic field.
I OUT = + or - 1 mA max to stay within accuracy.
Maximum measurable Gauss is just a bit less than 2,000 Gauss.
1 - VCC (5 V) @ 10 mA
2 - GND
3 - V OUT
Ratiometric - This term implies that the output will vary in proportion to the VCC voltage. VCC must be regulated and well filtered for proper operation of this device.
This is the one mentioned in the Slot Tech Magazine article.
Hall Effect Switches
Not all Hall Effect Devices are analog. There are also digital devices that might better be called a Hall Effect Switch. The output is either on or off. Usually these are Open-Collector outputs. The output can drive low when active (on or operating) or the output is off. These come in Unipolar, Bipolar and Latching types.
Unipolar - Typically always positive, the output goes low at one (higher B+ Gauss) level and releases at a lower Gauss level (also B+).
Bipolar - The device operates (turns on, output goes low) at a positive Gauss level and releases (turns off, output is not pulled low) at a negative (B-) Gauss level.
Latching - The device operates at a positive Gauss level and stays that way until a negative Gauss level is experienced. It stays that way until the positive Gauss level is reached again.
A3240EUA (1718938, Jameco, $0.93) "40E"
Unipolar Hall Effect Switch
1 - VCC (4.2 V to 24 V) 12 V typical @ 3.5 mA
2 - GND
3 - V OUT (OC, 24 mA max, 24 V)
Operating Point 35 to 50 G (output goes low)
Release Point 5 to 25 G (output goes high)
Hysteresis of 10 Gauss typical
Hysteresis - The actual operating points may vary from manufacturing batch to batch. It will also drift with temperature, but the difference between the two points should be about the same. For example the A3240EUA is stated as having an Operating point of 35 Gauss and a Release point of 25 Gauss. This gives a hysteresis of 10 Gauss. On any device these levels may vary, It may Operate at 40 Gauss and release at 30 Gauss. That is still a 10 Gauss hysteresis. All Hall Effect devices have this characteristic.
Chopper Stabilized Precision
SS411A
(1915843, Jameco, $1.79)
Bipolar
60 G (6 mT) Operate
-60 G (-6 mT) Release
VCC - 3.8 V to 30 V. Typically 12 V @ 10 mA Icc.
Pullup resistor - 1,600 Ohms when working at 12 V.
SS413A
Bipolar
140 G (14 mT) Operate
-140 G (-14 mT) Release
VCC - 3.8 V to 30 V. Typically 12 V @ 10 mA Icc.
Pullup resistor - 1,600 Ohms when working at 12 V.
SS41
(1915835, Jameco, $1.81) "S41"
Bipolar
40 G (4 mT) Operate
-40 G (-4 mT) Release
VCC - 4.5 V to 24 V. Typically 12 V @ 4 mA Icc.
Pullup resistor - 1,600 Ohms when working at 12 V.
SS441A
(1915886, Jameco, $1.79) "41A"
Unipolar
115 G (11.5 mT) Operate
20 G (2 mT) Release
VCC - 3.8 V to 30 V. Typically 12 V @ 10 mA Icc.
Pullup resistor - 1,600 Ohms when working at 12 V.
SS443A
Unipolar
"43A"
180 G (18 mT) Operate
75 G (7.5 mT) Release
VCC - 3.8 V to 30 V. Typically 12 V @ 10 mA Icc.
Pullup resistor - 1,600 Ohms when working at 12 V.
SS449A
Unipolar
"49A"
390 G (39 mT) Operate
235 G (23.5 mT) Release
VCC - 3.8 V to 30 V. Typically 12 V @ 10 mA Icc.
Pullup resistor - 1,600 Ohms when working at 12 V.
SS461A
Latching, Bipolar
"61A"
85 G (8.5 mT) Operate
-85 G (-8.5 mT) Release
VCC - 3.8 V to 30 V. Typically 12 V @ 10 mA Icc.
Pullup resistor - 1,600 Ohms when working at 12 V.
SS466A
(1915915, Jameco, $1.59)
"66A"
Latching, Bipolar
180 G (18 mT) Operate
-180 G (-18 mT) Release
VCC - 3.8 V to 30 V. Typically 12 V @ 10 mA Icc.
Pullup resistor - 1,600 Ohms when working at 12 V.
AH182PL
(319100, Jameco, $0.83)
DN6849SE
(DN6849SE-ND, Digikey, $1.51)
Bipolar, +175 Gauss operation, -175 Gauss release. Open Collector output. Icc = 6 mA. I Out = 20 mA (max).
DN8897
(DN8897-ND, Digikey, $1.69)
Bipolar, +120 Gauss operation, -120 Gauss release. Open Collector with 27K Ohm internal pull-up resistor included. . Icc = 6 mA. I Out = 20 mA (max).
Purchasing stuff
Most of the Hall Effect Devices included or mentioned in this course are available from Jameco Electronics (www.jameco.com).
Magnets are readily available from DigiKey Electronics (www.digikey.com).
Magnets
(Digi-Key)
469-1004-ND (DK, $0.20), 1/4" diameter, 1/8" thick, about 2,000 G.
Neodymium Iron Boron (NdFeB), nickel plated. They are very strong for their size. This is the one included in the course.
Also available:
469-1000-ND (DK, $2.05). 1" diameter, 1/8" thick
469-1001-ND (DK, $1.20). 3/4" diameter, 1/8" thick
469-1002-ND (DK, $0.60). 1/2" diameter, 1/8" thick
469-1003-ND (DK, $0.36). 1/4" diameter, 1/4" thick
469-1005-ND (DK, $0.13). 1/4" diameter, 1/16" thick
469-1006-ND (DK, $4.80). 1" x 2" bar, 1/8" thick
469-1007-ND (DK, $7.95). 1" x 2" bar, 1/4" thick
(All the above are advertised in the catalog as having 10,800 Gauss. The 469-1004 mentioned above was the one bought and it measured about 2,000 G. I have doubts about the advertisement.)
HE513-ND (DK, $3.41) H-34 (Hamlin), 6.35 mm square, 25.4 mm long, 260 Gauss
(this one was actually purchased and measured about 1,000 G)
HE510-ND (DK, $1.20) H-31 (Hamlin), 1.57 mm square, 12.70 mm long bar, 45 Gauss
HE511-ND (DK, $2.99) H-32 (Hamlin), 4.83 mm square, 25.4 mm long bar, 200 Gauss
HE512-ND (DK, $1.63) H-33 (Hamlin), 3.2 mm square, 19.1 mm long bar, 135 Gauss
HE155-ND (DK, $1.85) 315 (Hamlin), 3.05 mm diameter, 15 mm long rod, 120 Gauss
HE154-ND (DK, $1.98) H-36 (Hamlin), 4.62 mm diameter, 25.4 mm long rod, 155 G
HE514-ND (DK, $1.59) 420 (Hamlin), 3.81 mm diameter, 19.8 mm long rod, 175 Gauss