Magnetometer - Revision history

Shawn: /* Version with smaller MCU, i2C LCD display */

2019-04-23T17:12:59Z

Version with smaller MCU, i2C LCD display

← Older revision		Revision as of 10:12, 23 April 2019
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	====Version with smaller MCU, i2C LCD display====		====Version with smaller MCU, i2C LCD display====
	;PICAXE 08M2:This micro-controller has only eight pins and is very inexpensive.		;PICAXE 08M2:This micro-controller has only eight pins and is very inexpensive.
	;Newhaven i2c LCD display:The PICAXE 08M2 only has three available output pins after we use one for the ADC, so we cannot use SPI-based LCD displays. However, since the Hall sensor works at a minimum of 4V but the Newhaven display works at a maximum of 3.3V, we need to power and communicate with the Newhaven display through ~~voltage-dropping diodes~~.		;Newhaven i2c LCD display:The PICAXE 08M2 only has three available output pins after we use one for the ADC, so we cannot use SPI-based LCD displays. However, since the Hall sensor works at a minimum of 4V but the Newhaven display works at a maximum of 3.3V, we need to power and communicate with the Newhaven display through a level shifter.

	===Power supply===		===Power supply===

Shawn: /* See also */

2014-03-17T15:47:40Z

Shawn: /* See also */

2014-03-17T15:46:14Z

Shawn: /* Datasheets */ added PICAXE

2014-03-16T18:48:15Z

Datasheets: added PICAXE

← Older revision		Revision as of 11:48, 16 March 2014
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	;Sitronix ST7036 LCD Controller:The controller for the EA DOGM LCD displays. http://www.lcd-module.de/eng/pdf/zubehoer/st7036.pdf		;Sitronix ST7036 LCD Controller:The controller for the EA DOGM LCD displays. http://www.lcd-module.de/eng/pdf/zubehoer/st7036.pdf
	;ST Microelectronics L7805CV 5V regulator:http://www.st.com/web/en/resource/technical/document/datasheet/CD00000444.pdf		;ST Microelectronics L7805CV 5V regulator:http://www.st.com/web/en/resource/technical/document/datasheet/CD00000444.pdf
			;PICAXE micro-controller system for education:http://picaxe.com

	===See also===		===See also===

Shawn: /* Program */

2014-03-14T20:47:16Z

Program

← Older revision		Revision as of 13:47, 14 March 2014
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	===Program===		===Program===
			See [[Magnetometer PICAXE 20M2 program]] for a working example.

	====Reading the output voltage of the sensor====		====Reading the output voltage of the sensor====
	Digitize the voltage output from the Hall sensor with an ADC converter. Many micro-controllers include an ADC with enough resolution for pedagogical purposes, usually 10-12 bits. If the output of the Hall sensor output the full range of the ADC, then we'd have at least 1 in 1000 precision (2^10 is 1024). But usually the output will be only about half of that range, so for 10 bits we'd have a precision of 1 in 500.		Digitize the voltage output from the Hall sensor with an ADC converter. Many micro-controllers include an ADC with enough resolution for pedagogical purposes, usually 10-12 bits. If the output of the Hall sensor output the full range of the ADC, then we'd have at least 1 in 1000 precision (2^10 is 1024). But usually the output will be only about half of that range, so for 10 bits we'd have a precision of 1 in 500.

Shawn: /* Datasheets */

2014-03-14T20:14:36Z

Datasheets

← Older revision		Revision as of 13:14, 14 March 2014
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	;Everlight ELD-515 two-digit, seven-segment LED display:http://www.everlight.com/datasheets/D515SURWA-S530-A3_datasheet.pdf		;Everlight ELD-515 two-digit, seven-segment LED display:http://www.everlight.com/datasheets/D515SURWA-S530-A3_datasheet.pdf
	;Honeywell SS49/SS19 Series Analog Position Sensors (Hall effect sensors):http://www.mouser.com/ds/2/187/SS49-185687.pdf		;Honeywell SS49/SS19 Series Analog Position Sensors (Hall effect sensors):http://www.mouser.com/ds/2/187/SS49-185687.pdf
			:While the datasheet states no damage will be caused by fields greater than 1000 Gauss, it does not indicate how such fields affect the output.
	;Sitronix ST7036 LCD Controller:The controller for the EA DOGM LCD displays. http://www.lcd-module.de/eng/pdf/zubehoer/st7036.pdf		;Sitronix ST7036 LCD Controller:The controller for the EA DOGM LCD displays. http://www.lcd-module.de/eng/pdf/zubehoer/st7036.pdf
	;ST Microelectronics L7805CV 5V regulator:http://www.st.com/web/en/resource/technical/document/datasheet/CD00000444.pdf		;ST Microelectronics L7805CV 5V regulator:http://www.st.com/web/en/resource/technical/document/datasheet/CD00000444.pdf

Shawn: /* Program */

2014-03-14T20:06:16Z

Program

← Older revision		Revision as of 13:06, 14 March 2014
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	====Reading the output voltage of the sensor====		====Reading the output voltage of the sensor====
	Digitize the voltage output from the Hall sensor with an ADC converter. Many micro-controllers include an ADC with enough resolution for pedagogical purposes, usually 10-12 bits. If the output of the Hall sensor output the full range of the ADC, then we'd have at least 1 in 1000 precision (2^10 is 1024). But usually the output will be only about half of that range, so for 10 bits we'd have a precision of 1 in 500.		Digitize the voltage output from the Hall sensor with an ADC converter. Many micro-controllers include an ADC with enough resolution for pedagogical purposes, usually 10-12 bits. If the output of the Hall sensor output the full range of the ADC, then we'd have at least 1 in 1000 precision (2^10 is 1024). But usually the output will be only about half of that range, so for 10 bits we'd have a precision of 1 in 500.


			====Displaying the digits on a shared-pin LED display====
			To display a value between 1 and 999 as just two digits, if the value is below 100 we display the ones and tens with a decimal point between them, else we divide the value by 10 and display the resulting tens and ones with a decimal point on the right; i.e., the decimal point always is between the tens and ones, and we declare that we're displaying decaGauss, not Gauss.

	To convert a two-digit decimal value to individual characters, we set the variable TENS to the value divided by ten (all maths are in integers), and the variable ONES to the value modulo ten.		To convert a two-digit decimal value to individual characters, we set the variable TENS to the value divided by ten (all maths are in integers), and the variable ONES to the value modulo ten.

	~~====Displaying the digits on a shared-pin LED display====~~
	Since the two digits share the same cathode-pins, we can only show one at a time. We flip back and forth so quickly, about five thousand times a second, that it's imperceivable. The value of each digit is stored in a byte of memory, actually not the value [0-9] but the combination of bits to make the right LEDs on the display light up. For example, '8' requires all seven bits, while '7' requires just the first three.		Since the two digits share the same cathode-pins, we can only show one at a time. We flip back and forth so quickly, about five thousand times a second, that it's imperceivable. The value of each digit is stored in a byte of memory, actually not the value [0-9] but the combination of bits to make the right LEDs on the display light up. For example, '8' requires all seven bits, while '7' requires just the first three.

	====Displaying the digits on a serial LCD====		====Displaying the digits on a serial LCD====
	Every time we take a reading we clear the LCD. Then we send a negative sign if needed. We add an offset to each variable (TENS, ONES) equal to the value of 0 in the character map of the LCD, then send TENS ~~then~~ ONES to the LCD.		Every time we take a reading we clear the LCD. Then we send a negative sign if needed. We add an offset to each variable (HUNDREDS, TENS, ONES) equal to the value of 0 in the character map of the LCD, then send that offset HUNDREDS, TENS, and ONES to the LCD.

			====Sending the value to the serial port====
			Optionally, we can also send the raw ADC values and/or the calculated results to a computer or other device via another serial pin. Pin 19 of the PICAXE 20M2 operates at 4800 baud 8N1.

	===Datasheets===		===Datasheets===

Shawn: /* Version with larger MCU, SPI LCD display */

2014-03-14T16:51:37Z

Version with larger MCU, SPI LCD display

← Older revision		Revision as of 09:51, 14 March 2014
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	====Version with larger MCU, SPI LCD display====		====Version with larger MCU, SPI LCD display====
			Thanks to the low power consumption of this display, the whole circuit uses merely 6mA.
	;PICAXE 20M2:This micro-controller has enough pins to read ADC and output 4 SPI pins. We could also use the PIXAXE 14M2.		;PICAXE 20M2:This micro-controller has enough pins to read ADC and output 4 SPI pins. We could also use the PIXAXE 14M2.
	;Electronic Assembly DOGM081W-A:An LCD display with 8 digits and an ST7036 controller capable of SPI communications over four wires.		;Electronic Assembly DOGM081W-A:An LCD display with 8 digits and an ST7036 controller capable of SPI communications over four wires.

Shawn: /* Specifications */

2014-03-14T16:49:21Z

Specifications

← Older revision		Revision as of 09:49, 14 March 2014
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	===Specifications===		===Specifications===
	*Use a Hall effect sensor for repeatable measurements.		*Use a ratiometric Hall effect sensor for repeatable measurements.
	*Include at least two-digits display, ~~preferably with~~ floating point.		*Include at least two-digits display, using floating point if two.
	*Use a breadboard so it can be modified.		*Use a breadboard so it can be modified.
	*Provide a steady reference voltage to the sensor so that output is accurate.		*Provide a steady reference voltage to the sensor so that output is accurate.
			*Indicate direction of magnetic field and a number proportional to the voltage of the ratiometric sensor.
			====Possible improvements====
			*Allow a momentary-on button to allow the user to zero the readout.
			*Calibrate linearly, with a menu to allow setting high and low points.
			*Calibrate with a lookup table.

	===Circuit===		===Circuit===

Shawn at 16:43, 14 March 2014

2014-03-14T16:43:54Z

← Older revision		Revision as of 09:43, 14 March 2014
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	===Power supply===		===Power supply===
			[[File:Voltage-regulator-circuit.png\|256px\|thumb\|right\|A typical 5V regulated circuit, with protective diode and output capacitor. The input voltage must be greater than the dropout voltage of the regulator plus the voltage of the diode plus the output voltage (see a data-sheet).]]
	We can use three AAA or AA cells which would provide 3.6V to 5.1V, or one lithium 3.7V cell. Or, we can use a 9V battery with a voltage regulator. Or a 3V to 5V wall adapter would work, although reduce portability in measuring fields in multiple locations. A regulated 5V supply will reduce the need for frequent calibration. The microcontroller will use a few mA, the LCD and sensor less than a quarter mA each, so you should get roughly a hundred hours of use from a set of 4 AAA batteries or 5-6 AAA batteries with a regulator, or at least 10 hours of use from a 9V battery with a regulator.		We can use three AAA or AA cells which would provide 3.6V to 5.1V, or one lithium 3.7V cell. Or, we can use a 9V battery with a voltage regulator. Or a 3V to 5V wall adapter would work, although reduce portability in measuring fields in multiple locations. A regulated 5V supply will reduce the need for frequent calibration. The microcontroller will use a few mA, the LCD and sensor less than a quarter mA each, so you should get roughly a hundred hours of use from a set of 4 AAA batteries or 5-6 AAA batteries with a regulator, or at least 10 hours of use from a 9V battery with a regulator.

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	;Honeywell SS49/SS19 Series Analog Position Sensors (Hall effect sensors):http://www.mouser.com/ds/2/187/SS49-185687.pdf		;Honeywell SS49/SS19 Series Analog Position Sensors (Hall effect sensors):http://www.mouser.com/ds/2/187/SS49-185687.pdf
	;Sitronix ST7036 LCD Controller:The controller for the EA DOGM LCD displays. http://www.lcd-module.de/eng/pdf/zubehoer/st7036.pdf		;Sitronix ST7036 LCD Controller:The controller for the EA DOGM LCD displays. http://www.lcd-module.de/eng/pdf/zubehoer/st7036.pdf
			;ST Microelectronics L7805CV 5V regulator:http://www.st.com/web/en/resource/technical/document/datasheet/CD00000444.pdf

	===See also===		===See also===

← Older revision		Revision as of 08:47, 17 March 2014
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	[[Electronic circuits]] gives general tips on breadboards and their use.		[[Electronic circuits]] gives general tips on breadboards and their use.

			[[Circuits for teaching physics]] discusses a rationale for having students build circuits like this magnetometer in physics classes.

	[[Category:Electronics]]		[[Category:Electronics]]

← Older revision		Revision as of 08:46, 17 March 2014
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	[http://sensing.honeywell.com/index.php?ci_id=56091 Hall Effect Sensing and Application] by Honeywell.		[http://sensing.honeywell.com/index.php?ci_id=56091 Hall Effect Sensing and Application] by Honeywell.

			[[Electronic circuits]] gives general tips on breadboards and their use.

	[[Category:Electronics]]		[[Category:Electronics]]