Encoder Primer - Revision history

Mparadis: /* Interpreting the data */

2014-02-24T19:37:57Z

Interpreting the data

← Older revision		Revision as of 19:37, 24 February 2014
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	==Interpreting the data==		==Interpreting the data==
	~~It is all well and good to~~ know how an encoder works and what kind of signal it outputs ~~etc... but~~ how do we actually translate this into a position or velocity? Lets have a look at some typical numbers to get an idea:		Now that we know how an encoder works and what kind of signal it outputs, how do we actually translate this into a position or velocity? Lets have a look at some typical numbers to get an idea:

	Suppose we have a quadrature encoder that is connected to the rear shaft of a DC motor. When we first power everything up the encoder will read the default position of 0. This is always the case since the encoder's "home" position is whatever position it is in when you begin measuring. Now lets say the motor is energized and left running until the output shaft completes one full revolution. At this point the encoder should read ±CPR, so if we have a 360 CPR encoder (a fairly common value since it equates to 1° per tick) we should be at position=360 or position=-360 depending which direction the motor was rotated. With Phidget's encoder interfaces you have an event that gets generated every time there is a position change to a maximum of every 8ms. If there is more than 1 change in the 8ms period the event will report the total change in that period in one number. So if for example the position starts at 0, goes to 60, then returns to 40 within 8ms you will see a change of +40. In addition to this, the Phidget's encoder interfaces will report the amount of time that this position change occurred over. With those two pieces of information you can calculate the velocity of the motor as X ticks over Y milliseconds. From there it is easy to convert to RPM or some other desirable unit.		Suppose we have a quadrature encoder that is connected to the rear shaft of a DC motor. When we first power everything up the encoder will read the default position of 0. This is always the case since the encoder's "home" position is whatever position it is in when you begin measuring. Now lets say the motor is energized and left running until the output shaft completes one full revolution. At this point the encoder should read ±CPR, so if we have a 360 CPR encoder (a fairly common value since it equates to 1° per tick) we should be at position=360 or position=-360 depending which direction the motor was rotated. With Phidget's encoder interfaces you have an event that gets generated every time there is a position change to a maximum of every 8ms. If there is more than 1 change in the 8ms period the event will report the total change in that period in one number. So if for example the position starts at 0, goes to 60, then returns to 40 within 8ms you will see a change of +40. In addition to this, the Phidget's encoder interfaces will report the amount of time that this position change occurred over. With those two pieces of information you can calculate the velocity of the motor as X ticks over Y milliseconds. From there it is easy to convert to RPM or some other desirable unit.

Burley: /* How to use this data */

2013-10-10T20:41:36Z

How to use this data

← Older revision		Revision as of 20:41, 10 October 2013
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	==~~How~~ to ~~use~~ this ~~data~~==		==Interpreting the data==
			It is all well and good to know how an encoder works and what kind of signal it outputs etc... but how do we actually translate this into a position or velocity? Lets have a look at some typical numbers to get an idea:

			Suppose we have a quadrature encoder that is connected to the rear shaft of a DC motor. When we first power everything up the encoder will read the default position of 0. This is always the case since the encoder's "home" position is whatever position it is in when you begin measuring. Now lets say the motor is energized and left running until the output shaft completes one full revolution. At this point the encoder should read ±CPR, so if we have a 360 CPR encoder (a fairly common value since it equates to 1° per tick) we should be at position=360 or position=-360 depending which direction the motor was rotated. With Phidget's encoder interfaces you have an event that gets generated every time there is a position change to a maximum of every 8ms. If there is more than 1 change in the 8ms period the event will report the total change in that period in one number. So if for example the position starts at 0, goes to 60, then returns to 40 within 8ms you will see a change of +40. In addition to this, the Phidget's encoder interfaces will report the amount of time that this position change occurred over. With those two pieces of information you can calculate the velocity of the motor as X ticks over Y milliseconds. From there it is easy to convert to RPM or some other desirable unit.

			Something to remember when trying to calculate the RPM of the motor is that if your motor has a gear box the encoder is mounted to the rear shaft which is NOT affected by the gear box. This means that the RPM measured by the encoder will not match the apparent RPM of the motor, you need to factor in the gear ratio to get the proper RPM.

	==Conclusion==		==Conclusion==

Burley: /* Interference */

2013-10-10T20:02:32Z

Interference

← Older revision		Revision as of 20:02, 10 October 2013
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			==How to use this data==

	==Conclusion==		==Conclusion==

Mparadis: /* Single-Ended Signal */

2012-09-25T16:06:34Z

Single-Ended Signal

← Older revision		Revision as of 16:06, 25 September 2012
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	In the case of mechanical encoders, the brushes simply switch to ground without any complex circuitry.		In the case of mechanical encoders, the brushes simply switch to ground without any complex circuitry.
	The most basic optical encoders will similarly use phototransistors to switch to ground. This method is called '''"Open Collector"'''. These devices require pull-up resistors in order to generate the output waveform. They may be included in the encoder, or they may rely on the encoder interface to provide them. Phidget Inc.'s encoder interfaces come with fairly weak pull-up resistors built in. If your encoder's data sheet specifies that it requires an external pull-up resistance greater than what the Phidgets Inc. interface provides, you won't be able to use the encoder with a Phidgets Inc. interface. If your encoder needs a lower pull-up resistance (and therefore, a '''stronger''' pull-up resistor in parallel), it may still work, but at a lower response rate. If you want to make the pull-up resistor stronger, you can add pull-up resistors on the A, and B channels (and the index channel, if applicable) on the encoder cable. When choosing the resistance '''R''' for the pull-up, use the formula below (Existing resistance can be found in the data sheet of the encoder interface, and desired resistance is the pull-up resistance specified in the encoder's data sheet).		The most basic optical encoders will similarly use phototransistors to switch to ground. This method is often called '''"Open Collector"''' or '''"Current Sinking"'''. These devices require pull-up resistors in order to generate the output waveform. They may be included in the encoder, or they may rely on the encoder interface to provide them. Phidget Inc.'s encoder interfaces come with fairly weak pull-up resistors built in. If your encoder's data sheet specifies that it requires an external pull-up resistance greater than what the Phidgets Inc. interface provides, you won't be able to use the encoder with a Phidgets Inc. interface. If your encoder needs a lower pull-up resistance (and therefore, a '''stronger''' pull-up resistor in parallel), it may still work, but at a lower response rate. If you want to make the pull-up resistor stronger, you can add pull-up resistors on the A, and B channels (and the index channel, if applicable) on the encoder cable. When choosing the resistance '''R''' for the pull-up, use the formula below (Existing resistance can be found in the data sheet of the encoder interface, and desired resistance is the pull-up resistance specified in the encoder's data sheet).


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	[[File:Encoder-pull-up.jpg\|450px\|link=\|'''Adding Pull-Up Resistors'''<br/>This diagram shows the basic modification you can make to the encoder cable to reduce pull-up resistance. <br/>[[Media:Encoder-pull-up.jpg\|Full-sized Image]]]]		[[File:Encoder-pull-up.jpg\|450px\|link=\|'''Adding Pull-Up Resistors'''<br/>This diagram shows the basic modification you can make to the encoder cable to reduce pull-up resistance. <br/>[[Media:Encoder-pull-up.jpg\|Full-sized Image]]]]

	A '''"Line Drive"''' output circuit is the opposite of an open collector output- each phototransistor is connected to a pull-up resistor, so they need pull-down resistors or a sinking input to generate the output waveform. Phidgets Inc. encoder interfaces will not work with line drive encoders, because the interface does not come with built in pull-down resistors.		A '''"Line Drive"''' (sometimes called a '''"Current Sourcing"''') output circuit is the opposite of an open collector output- each phototransistor is connected to a pull-up resistor, so they need pull-down resistors or a sinking input to generate the output waveform. Phidgets Inc. encoder interfaces will not work with line drive encoders, because the interface does not come with built in pull-down resistors.

	Another output circuit design called '''"Push-pull"''' combines the two methods above, connecting each phototransistor to both a pull-up and a pull-down resistor. A push-pull encoder will still work with a Phidgets Inc. encoder interface; the built-in pull-up resistors are unnecessary but won't cause any problems. Push-pull encoders are desirable because the output waveform can quickly transition from 0 to 5V. A shorter transition time allows the encoder to track faster movement. Another advantage of push-pull is that the output signal is less susceptible to electromagnetic interference, because the output is always supplied directly by either +5V or ground.		Another output circuit design called '''"Push-pull"''' combines the two methods above, connecting each phototransistor to both a pull-up and a pull-down resistor. A push-pull encoder will still work with a Phidgets Inc. encoder interface; the built-in pull-up resistors are unnecessary but won't cause any problems. Push-pull encoders are desirable because the output waveform can quickly transition from 0 to 5V. A shorter transition time allows the encoder to track faster movement. Another advantage of push-pull is that the output signal is less susceptible to electromagnetic interference, because the output is always supplied directly by either +5V or ground.

Burley: /* Products that fall under this category */

2012-08-10T17:48:37Z

Products that fall under this category

← Older revision		Revision as of 17:48, 10 August 2012
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	Encoders can be susceptible to [[#Interference\|interference]], especially when there is a long wire between the encoder and the encoder interface. This problem can be mitigated by adding shielded cable or using a differential encoder instead.		Encoders can be susceptible to [[#Interference\|interference]], especially when there is a long wire between the encoder and the encoder interface. This problem can be mitigated by adding shielded cable or using a differential encoder instead.

	~~==Products that fall under this category==~~
	*[http://www.phidgets.com/products.php?product_id=1047 1047 - PhidgetEncoder HighSpeed 4-Input]
	*[http://www.phidgets.com/products.php?product_id=1057 1057 - PhidgetEncoder HighSpeed]
	*[http://www.phidgets.com/products.php?product_id=1052 1052 - PhidgetEncoder]]
	*[http://www.phidgets.com/products.php?product_id=3530 3530 - Optical Rotary Encoder ISC3004]]
	*[http://www.phidgets.com/products.php?category=24 DC Motors (Models with 'E' in their part number have an encoder attached)]

Burley: /* Encoder Interfaces */

2012-08-10T17:48:10Z

Encoder Interfaces

← Older revision		Revision as of 17:48, 10 August 2012
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	===Encoder Interfaces===		===Encoder Interfaces===

	An encoder interface is a device that converts encoder data into a useful format, such as number of counts and direction of rotation. For example, the [~~http://www.phidgets.com~~/products.php?product_id=1057 1057 - PhidgetEncoder HighSpeed] reads in a pair of quadrature signals, and uses them to continually update the position of the encoder, automatically taking care of direction changes. These updates are sent to your computer via USB, and when your program makes a call to get the encoder's position, it retrieves the latest value that has been sent. The speed at which these updates occur is called the '''Software Update Rate'''. The encoder interface will also typically provide operating power to the encoder. Phidgets Inc. encoder interfaces supply +5V, which is a common voltage requirement for many encoders. If you're planning on using an optical encoder with one of our encoder interfaces, you should make sure that it's rated for +5V operation. Mechanical encoders, on the other hand, usually don't require the +5V pin at all- they just use the pull-up voltage on the data lines and switch to ground to generate the signal.		An encoder interface is a device that converts encoder data into a useful format, such as number of counts and direction of rotation. For example, the [{{SERVER}}/products.php?product_id=1057 1057 - PhidgetEncoder HighSpeed] reads in a pair of quadrature signals, and uses them to continually update the position of the encoder, automatically taking care of direction changes. These updates are sent to your computer via USB, and when your program makes a call to get the encoder's position, it retrieves the latest value that has been sent. The speed at which these updates occur is called the '''Software Update Rate'''. The encoder interface will also typically provide operating power to the encoder. Phidgets Inc. encoder interfaces supply +5V, which is a common voltage requirement for many encoders. If you're planning on using an optical encoder with one of our encoder interfaces, you should make sure that it's rated for +5V operation. Mechanical encoders, on the other hand, usually don't require the +5V pin at all- they just use the pull-up voltage on the data lines and switch to ground to generate the signal.

	Even if you're up to the task of trying to decode the quadrature signal yourself in software, we do not recommend it, because the [[Digital Input Primer\|Digital Inputs]] on Phidgets devices do not sample fast enough to detect a quadrature signal.		Even if you're up to the task of trying to decode the quadrature signal yourself in software, we do not recommend it, because the [[Digital Input Primer\|Digital Inputs]] on Phidgets devices do not sample fast enough to detect a quadrature signal.

Mparadis: /* List of encoders */

2012-07-30T14:27:15Z

List of encoders

← Older revision		Revision as of 14:27, 30 July 2012
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	*[http://www.phidgets.com/products.php?product_id=3530 3530 - Optical Rotary Encoder ISC3004]]		*[http://www.phidgets.com/products.php?product_id=3530 3530 - Optical Rotary Encoder ISC3004]]
	*[http://www.phidgets.com/products.php?category=24 DC Motors (Models with 'E' in their part number have an encoder attached)]		*[http://www.phidgets.com/products.php?category=24 DC Motors (Models with 'E' in their part number have an encoder attached)]

	~~=List of encoders=~~
	* Sourced from Digikey
	* Customers should look for encoders that advertise 'Quadrature'
	* Encoders often advertise 'detents' - which are perceptible clicks as the encoder is rotated. Encoders with detents are usually meant for operation by people as control knobs.
	* Encoders for manual (people) operation will often have a built in pushbutton switch on the shaft. This functionality is seperate from the encoder. Encoder interfaces available from Phidgets will often have support for digital inputs - this switch can be wired in to a digital input.

	~~==Mechanical encoders==~~
	* Mechnical encoders are usually very cheap, and meant for manual (people) operation.
	* Mechanical encoders will have a shorter lifespan, measured in the number of rotations.

Mparadis: /* Glossary */

2012-07-30T14:27:00Z

Glossary

@@ Line 188: / Line 188: @@
 *[http://www.phidgets.com/products.php?product_id=3530 3530 - Optical Rotary Encoder ISC3004]]
 *[http://www.phidgets.com/products.php?category=24 DC Motors (Models with 'E' in their part number have an encoder attached)]
 =List of encoders=

Mparadis: /* Connector */

2012-07-30T14:11:59Z

Connector

← Older revision		Revision as of 14:11, 30 July 2012
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	The four-wire encoders still use a 5-wire connector, with the index wire not included. This means you can still use these encoders with encoder interfaces that normally accept 5-wire encoders.		The four-wire encoders still use a 5-wire connector, with the index wire not included. This means you can still use these encoders with encoder interfaces that normally accept 5-wire encoders.

			The connector used on Phidgets boards is the '''Molex 70553-0004'''. If you need this connector or mating connectors, you can find them on a site like [http://www.digikey.com digikey].

	Here's a list of encoder cables available at Phidgets Inc.:		Here's a list of encoder cables available at Phidgets Inc.:

Mparadis: /* Connector */

2012-07-30T14:06:03Z

Connector

← Older revision		Revision as of 14:06, 30 July 2012
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	Here's a list of encoder cables available at Phidgets Inc.:		Here's a list of encoder cables available at Phidgets Inc.:

	~~(table: +cable +needs_encoder_input)~~		{\| style="border:1px solid darkgray;" cellpadding="7px;"

	{\|border=1
	\|+'''Encoder Cables'''		\|+'''Encoder Cables'''
	! Phidgets Product #		\|-style="background: #d1d1d1" align=center
	! Connector Type		!Phidgets Product # \|\| Connector Type \|\| Length (cm)
	! Length (cm)
	\|-		\|-
	\| 3019_0 \|\| Molex 50-57-940 \|\| 50		\|style="background: #f0f0f0" align=center\| 3019_0
			\|style="background: #f0f0f0" align=center\| Molex 50-57-940
			\|style="background: #f0f0f0" align=center\| 50
	\|-		\|-
	\| 3032_0 \|\| E4P \|\| 50		\|style="background: #f0f0f0" align=center\| 3032_0
			\|style="background: #f0f0f0" align=center\| E4P
			\|style="background: #f0f0f0" align=center\| 50
	\|}		\|}