Mech - User contributions [en]

Analog Input

2008-12-11T12:30:39Z

StevenManuel:

You can assign from one to thirteen pins to be used as analog inputs. These pins are named AN0 through AN12. The set that you use as analog inputs must start with AN0 and must be contiguous, i.e. if you use AN0 and AN3 as analog inputs, you can't use AN1 and AN2 for a different purpose. A statement such as setup_adc_ports(AN0_TO_AN3) selects the range of pins to be used as analog inputs.

The input voltage range is 0 to 5V. Voltages outside this range can damage the PIC. The 0 to 5V range is converted by the PIC's ADC to an 8 or 10 bit positive integer, i.e. to a value 0-255 or 0-1023. A statement such as #DEVICE ADC=10 selects 8-bit or 10-bit ADC resolution.

There is really only one ADC in the PIC, and a bunch of analog switches to connect any one of the thirteen input pins to it. After a change of selected pin, e.g. with set_adc_channel(3) to select input pin AN3, a 10uS delay is recommended so that the ADC can lock in and digitize the new value, before you read it with read_ADC(). You can read_adc() with no delay if you haven't recently changed selected input pin.

In the demo program AnalogInput.c a 10-bit ADC conversion is done, with the low order 8 bits displayed on port D and the high 2 bits displayed on pins C0 and C1.

[[Image:analoginputpot.gif|right]]

Reading a trimpot

A simple source for a 0-5V analog level is a potentiometer (a.k.a. trimpot). One use is as an easily adjustable variable value to control operation ofyour program, or some gain factors; the kind of thing you might have otherwise done by querying the user in a text window. Here, just turn the pot.

Sample code

[http://peshkin.mech.northwestern.edu/pic/code Link to all sample code here.]

[[Image:analoginpic.gif|right]]

Reading a phototransistor

A typical circuit for reading light intensity with a phototransistor is shown at right. Greater light level causes a lower voltage at pin AN0, and a lower value read by the PIC's ADC.

Amplification and level shifting

The above circuit used a sensor without amplification, and the output voltage range was intrinsically limited to 0-5V by the supply rails of the circuit. If you wish to use an opamp or instrumentation amp to produce the voltage to be digitized, you will need to limit it to the 0-5V range, and possibly also to level-shift it so that both polarities of sensing are readable. There are many ways to accomplish these things.

The best way is to use a level of 2.5V as your "null" level. If you use a rail-to-rail opamp with supply rails of 0 and 5V, its output is naturally limited to the PIC's analog input range. One convenient way to produce the 2.5V without consuming power in a voltage divider is to use a rail splitter which provides a reference voltage exactly half way between the supply rails.

[[Image:AmplifiedPT.gif|right]]

Amplified phototransistor 

Above is an amplified phototransistor circuit, which provides 100-fold gain (1M/10K) and a high-pass filter with a time constant of 1mS (10Kohm * 100pF). Thus it responds sensitively to a rapid change in light level, probably caused by a strobed LED or IRED, while ignoring overall (DC) light level.

Strobing an LED or IRED briefly (e.g. 100uS) and infrequently (e.g. every 5 mS) allows you to use 10x the rated steady current, and get 10x more light, without overheating the LED. It also allows you to use a phototransistor circuit that responds only to changes, and your PIC software can compare the light level just before and during the flash. All of these allow greatly improved sensitivity.

The chip is a high-speed rail-to-rail opamp such as LM6132, with supply rails of 0 and 5V. Its non-inverting input is held at 2.5V by the voltage divider, and therefore this is the quiescent level of the inverting input as well -- and of the output. The ADC in 10-bit mode reads about 512.

Perhaps the voltage divider produces not exactly 2.5V, or the ADC maps 2.5V not to exactly half scale? The connection from the 2.5V reference point to analog input AN1 allows the PIC to determine the ADC result corresponding to quiescence.

tip - high gain high speed opamp circuits are often unstable, as you can observe with an oscilloscope (and only with an oscilloscope). Try to eliminate oscillations with a small capacitor (e.g. 10pF) across the feedback resistor (1M here). Always use a supply decoupling capacitor (e.g. 0.1uF) across the supply rails, right near the chip.

[[Image:InstAmp2.gif|right]]

Instrumentation amp

Instrumentation amps are often used with full- or half- strain gauge bridges (four or two strain gauge elements). A half-bridge is shown above. The gain of the instrumentation amp is set by a gain resistor according a to a formula in the datasheet, typically gain = 50K/Rgain.

For easy interfacing to a PIC's 0-5V analog input range, use a rail-to-rail instrumentation amp such as AD623. The instrumentation amp subtracts its two inputs, multiplies the difference by the gain, and adds on the reference voltage. Here we've used a reference voltage of zero, but we could have made it 2.5V by using a voltage divider. With a reference voltage of zero, which is preferable, how can we read deflections of the strain gauge bridge of both polarities? The 10K nulling trimpot allows us to set the quiescent output of the instrumentation amp to 2.5V. Alternately, you could use a rail splitter which is simply an IC that outputs the average of its two input rails, which in this case will be 0V and 5V. This method wastes far less current but cannot be trimmed to the ideal 2.5V in the case that your supply doesn't produce exactly 5V.

Often strain gauges need an amplification factor of 500 or even 1000. At these high gains, noise from nearby digital devices (such as a PIC) can cause erratic operation of the amplifier. Use supply decoupling capacitors (typically 0.1uF) near the chip, from both supply rails to Vref (ground here). If it is acceptable to low-pass the signal, use an appropriate capacitor between the inverting and non-inverting inputs of the instrumentation amp (e.g. for a 1mS low pass, C=0.1uF here, because 0.1uF * 10Kohm = 1mS). You can also use an RC low pass between the output of the instrumentation amp and the PIC input. In many cases you may need to use a standalone strain gauge amplifier board with its own power supply (see [xxx])

Analog Input

2008-12-11T12:24:27Z

StevenManuel: Added rail splitter to level shifting and instrumentation amp sections

You can assign from one to thirteen pins to be used as analog inputs. These pins are named AN0 through AN12. The set that you use as analog inputs must start with AN0 and must be contiguous, i.e. if you use AN0 and AN3 as analog inputs, you can't use AN1 and AN2 for a different purpose. A statement such as setup_adc_ports(AN0_TO_AN3) selects the range of pins to be used as analog inputs.

The input voltage range is 0 to 5V. Voltages outside this range can damage the PIC. The 0 to 5V range is converted by the PIC's ADC to an 8 or 10 bit positive integer, i.e. to a value 0-255 or 0-1023. A statement such as #DEVICE ADC=10 selects 8-bit or 10-bit ADC resolution.

There is really only one ADC in the PIC, and a bunch of analog switches to connect any one of the thirteen input pins to it. After a change of selected pin, e.g. with set_adc_channel(3) to select input pin AN3, a 10uS delay is recommended so that the ADC can lock in and digitize the new value, before you read it with read_ADC(). You can read_adc() with no delay if you haven't recently changed selected input pin.

In the demo program AnalogInput.c a 10-bit ADC conversion is done, with the low order 8 bits displayed on port D and the high 2 bits displayed on pins C0 and C1.

[[Image:analoginputpot.gif|right]]

Reading a trimpot

A simple source for a 0-5V analog level is a potentiometer (a.k.a. trimpot). One use is as an easily adjustable variable value to control operation ofyour program, or some gain factors; the kind of thing you might have otherwise done by querying the user in a text window. Here, just turn the pot.

Sample code

[http://peshkin.mech.northwestern.edu/pic/code Link to all sample code here.]

[[Image:analoginpic.gif|right]]

Reading a phototransistor

A typical circuit for reading light intensity with a phototransistor is shown at right. Greater light level causes a lower voltage at pin AN0, and a lower value read by the PIC's ADC.

Amplification and level shifting

The above circuit used a sensor without amplification, and the output voltage range was intrinsically limited to 0-5V by the supply rails of the circuit. If you wish to use an opamp or instrumentation amp to produce the voltage to be digitized, you will need to limit it to the 0-5V range, and possibly also to level-shift it so that both polarities of sensing are readable. There are many ways to accomplish these things.

The best way is to use a level of 2.5V as your "null" level. If you use a rail-to-rail opamp with supply rails of 0 and 5V, its output is naturally limited to the PIC's analog input range. One convenient way to produce the 2.5V for your instrumentation amp without wasting power in a voltage divider is to use a rail splitter which provides a reference voltage exactly half way between the supply rails.

[[Image:AmplifiedPT.gif|right]]

Amplified phototransistor 

Above is an amplified phototransistor circuit, which provides 100-fold gain (1M/10K) and a high-pass filter with a time constant of 1mS (10Kohm * 100pF). Thus it responds sensitively to a rapid change in light level, probably caused by a strobed LED or IRED, while ignoring overall (DC) light level.

Strobing an LED or IRED briefly (e.g. 100uS) and infrequently (e.g. every 5 mS) allows you to use 10x the rated steady current, and get 10x more light, without overheating the LED. It also allows you to use a phototransistor circuit that responds only to changes, and your PIC software can compare the light level just before and during the flash. All of these allow greatly improved sensitivity.

The chip is a high-speed rail-to-rail opamp such as LM6132, with supply rails of 0 and 5V. Its non-inverting input is held at 2.5V by the voltage divider, and therefore this is the quiescent level of the inverting input as well -- and of the output. The ADC in 10-bit mode reads about 512.

Perhaps the voltage divider produces not exactly 2.5V, or the ADC maps 2.5V not to exactly half scale? The connection from the 2.5V reference point to analog input AN1 allows the PIC to determine the ADC result corresponding to quiescence.

tip - high gain high speed opamp circuits are often unstable, as you can observe with an oscilloscope (and only with an oscilloscope). Try to eliminate oscillations with a small capacitor (e.g. 10pF) across the feedback resistor (1M here). Always use a supply decoupling capacitor (e.g. 0.1uF) across the supply rails, right near the chip.

[[Image:InstAmp2.gif|right]]

Instrumentation amp

Instrumentation amps are often used with full- or half- strain gauge bridges (four or two strain gauge elements). A half-bridge is shown above. The gain of the instrumentation amp is set by a gain resistor according a to a formula in the datasheet, typically gain = 50K/Rgain.

For easy interfacing to a PIC's 0-5V analog input range, use a rail-to-rail instrumentation amp such as AD623. The instrumentation amp subtracts its two inputs, multiplies the difference by the gain, and adds on the reference voltage. Here we've used a reference voltage of zero, but we could have made it 2.5V by using a voltage divider. With a reference voltage of zero, which is preferable, how can we read deflections of the strain gauge bridge of both polarities? The 10K nulling trimpot allows us to set the quiescent output of the instrumentation amp to 2.5V. Alternately, you could use a rail splitter which is simply an IC that outputs the average of its two input rails, which in this case will be 0V and 5V. This method wastes far less current but cannot be trimmed to the ideal 2.5V in the case that your supply doesn't produce exactly 5V.

Often strain gauges need an amplification factor of 500 or even 1000. At these high gains, noise from nearby digital devices (such as a PIC) can cause erratic operation of the amplifier. Use supply decoupling capacitors (typically 0.1uF) near the chip, from both supply rails to Vref (ground here). If it is acceptable to low-pass the signal, use an appropriate capacitor between the inverting and non-inverting inputs of the instrumentation amp (e.g. for a 1mS low pass, C=0.1uF here, because 0.1uF * 10Kohm = 1mS). You can also use an RC low pass between the output of the instrumentation amp and the PIC input. In many cases you may need to use a standalone strain gauge amplifier board with its own power supply (see [xxx])

Accelerometers

2008-12-09T00:24:34Z

StevenManuel:

[[image:mems accelerometer.png|right]]

Accelerometers measure linear acceleration and also gravity; the two are indistinguishable. Thus they unavoidably function as tilt sensors as well. Inexpensive 1, 2, and 3-axis accelerometers are available which are constructed with MEMS techniques.
MEMS gyroscopes are also available, for measuring angular velocity, but are more expensive.

 

[[Image:carrier.jpg|right]]

The LIS2L02AS4-TR accelerometer gives you a choice of +/-2g or +/-6g full scale. It needs only a single +5V supply. Its bandwidth is from DC to 1.5KHz. The output is usually low-pass filtered in applications which do not need the full 1.5KHz bandwidth, using an external capacitor.

The chip is available only in a surface-mount SO-24 package. Fortunately an adapter socket (Digikey A322-ND) can be used to give the chip convenient DIP-24 legs.

 

[[Image:somesoldered.jpg|right]]
Soldering the chip into the adapter socket is a little challenging. Here are some tricks that make it easier. The more of these you can take advantage of, the easier it will be.

* Use a very fine pointed soldering iron and fine solder.
* Apply a bead of liquid flux to the pads, which will make the solder flow in between the pin and the pad enthusiastically.
* Tape the chip down onto its socket adapter.
* Have a magnifying lens or loupe available.
* Know which pins are not used.

The last point is especially useful. Start with pin 1 which is NC (Not Connected), so that even if you get a solder blob connecting pins 1 & 2 that's ok. If the other pins are all aligned with their pads, pin 1's solder will now hold them there. If not, melt pin 1's solder and adjust.

[[Image:chip.gif|right]]

Now solder only the other pins that are in use, as shown in red on the diagram. Solder one or two on the opposite edge as well, for mechanical stability.

Pins marked "reserved" should not be solder-blobbed to their neighbors because we don't know what they connect to inside the chip. Reserved is not the same thing as NC.

 
[[Image:circuit.gif|right]]

Use a supply shunt near the chip (1uF) from +5 to ground). Use low-pass filter capacitors on the outputs (called Cload in the diagram). The output impedance of the chip is 110Kohm, so a 0.1uF capacitor gives a low pass time constant of ~10mS.

Tie ST, PD low, and FS low for +/-2g full scale operation. The output voltage ranges 0-5V, well matched to PIC inputs. 2.5V is the output when acceleration is zero and and the chip is horizontal (not tilted.)

The circuit shows some optional buffer amplifiers to produce a low impedance output.

== Accelerometers and Low Pass Filtering ==

When using accelerometers in applications with high ambient vibrations, filtering the output signal is essential for limiting noise. While in many cases first order (RC) low pass filters may be sufficient to attenuate ambient vibration, if those vibrations are great in magnitude and/or relatively close in frequency to the desired output, second order filtering may be necessary. In addition, in order to protect the accelerometer from sourcing excessive current and dropping its output voltage, it is advisable to use ''active'' rather than passive filtering. Both of these criteria are met by [[Second Order Active Filters]], specifically a second order active low pass filter.

The one major disadvantage of a second order filter is an increased maximum lag from 90 to 180 degrees but as with any filter, if C and R values are chosen carefully, the desired signal should not lie within that range.

Accelerometers

2008-12-09T00:23:09Z

StevenManuel: Added low pass filtering to the accelerometer page

[[image:mems accelerometer.png|right]]

Accelerometers measure linear acceleration and also gravity; the two are indistinguishable. Thus they unavoidably function as tilt sensors as well. Inexpensive 1, 2, and 3-axis accelerometers are available which are constructed with MEMS techniques.
MEMS gyroscopes are also available, for measuring angular velocity, but are more expensive.

 

[[Image:carrier.jpg|right]]

The LIS2L02AS4-TR accelerometer gives you a choice of +/-2g or +/-6g full scale. It needs only a single +5V supply. Its bandwidth is from DC to 1.5KHz. The output is usually low-pass filtered in applications which do not need the full 1.5KHz bandwidth, using an external capacitor.

The chip is available only in a surface-mount SO-24 package. Fortunately an adapter socket (Digikey A322-ND) can be used to give the chip convenient DIP-24 legs.

 

[[Image:somesoldered.jpg|right]]
Soldering the chip into the adapter socket is a little challenging. Here are some tricks that make it easier. The more of these you can take advantage of, the easier it will be.

* Use a very fine pointed soldering iron and fine solder.
* Apply a bead of liquid flux to the pads, which will make the solder flow in between the pin and the pad enthusiastically.
* Tape the chip down onto its socket adapter.
* Have a magnifying lens or loupe available.
* Know which pins are not used.

The last point is especially useful. Start with pin 1 which is NC (Not Connected), so that even if you get a solder blob connecting pins 1 & 2 that's ok. If the other pins are all aligned with their pads, pin 1's solder will now hold them there. If not, melt pin 1's solder and adjust.

[[Image:chip.gif|right]]

Now solder only the other pins that are in use, as shown in red on the diagram. Solder one or two on the opposite edge as well, for mechanical stability.

Pins marked "reserved" should not be solder-blobbed to their neighbors because we don't know what they connect to inside the chip. Reserved is not the same thing as NC.

 
[[Image:circuit.gif|right]]

Use a supply shunt near the chip (1uF) from +5 to ground). Use low-pass filter capacitors on the outputs (called Cload in the diagram). The output impedance of the chip is 110Kohm, so a 0.1uF capacitor gives a low pass time constant of ~10mS.

Tie ST, PD low, and FS low for +/-2g full scale operation. The output voltage ranges 0-5V, well matched to PIC inputs. 2.5V is the output when acceleration is zero and and the chip is horizontal (not tilted.)

The circuit shows some optional buffer amplifiers to produce a low impedance output.

'''Accelerometers and Low Pass Filtering'''
When using accelerometers in applications with high ambient vibrations, filtering the output signal is essential for limiting noise. While in many cases first order (RC) low pass filters may be sufficient to attenuate ambient vibration, if those vibrations are great in magnitude and/or relatively close in frequency to the desired output, second order filtering may be necessary. In addition, in order to protect the accelerometer from sourcing excessive current and dropping its output voltage, it is advisable to use ''active'' rather than passive filtering. Both of these criteria are met by [[Second Order Active Filters]], specifically a second order active low pass filter.

The one major disadvantage of a second order filter is an increased maximum lag from 90 to 180 degrees but as with any filter, if C and R values are chosen carefully, the desired signal should not lie within that range.

Second Order Active Filters

2008-12-09T00:07:55Z

StevenManuel:

2nd order active filtering has two main advantages:
* High impedance input, low impedance output
* greater attenuation at high range (-40dB/decade as opposed to -20dB/decade for RC filter)

The high input impedance provided by an op amp circuit protects the instrument providing the signal from passing excessive current which could cause a voltage drop in the measurement signal or damage to the instrument itself.

Because the filter is second order, the rolloff after the cutoff frequency on a bode plot of a 2nd order low pass filter for example, is -40 dB/decade as opposed to -20 dB/decade for a first order (RC) filter which means significantly greater attenuation outside the pass band and a sharper cutoff. This can be very useful if the noise frequency is close to the desired signal frequency.

[[Image:2ndOrderFilterDiagrams.gif]]

Where the cutoff frequency for both high and low pass filters in Hz is:

<math>f=1/(2*pi*sqrt(R_1 R_2 C_1 C_2))</math>

'''External Links'''

http://en.wikipedia.org/wiki/Sallen_Key_filter

Second Order Active Filters

2008-12-09T00:05:50Z

StevenManuel:

2nd order active filtering has two main advantages:
* High impedance input, low impedance output
* greater attenuation at high range (-40dB/decade as opposed to -20dB/decade for RC filter)

The high input impedance provided by an op amp circuit protects the instrument providing the signal from passing excessive current which could cause a voltage drop in the measurement signal or damage to the instrument itself.

Because the filter is second order, the rolloff after the cutoff frequency on a bode plot of a 2nd order low pass filter for example, is -40 dB/decade as opposed to -20 dB/decade for a first order (RC) filter which means significantly greater attenuation outside the pass band and a sharper cutoff. This can be very useful if the noise frequency is close to the desired signal frequency.

[[Image:2ndOrderFilterDiagrams.gif]]

Where the cutoff frequency for both high and low pass filters in Hz is:

<math>f=1/(2*pi*sqrt(R_1 R_2 C_1 C_2))</math>

References:
http://en.wikipedia.org/wiki/Sallen_Key_filter

Second Order Active Filters

2008-12-09T00:05:20Z

StevenManuel:

2nd order active filtering has two main advantages:
* High impedance input, low impedance output
* greater attenuation at high range (-40dB/decade as opposed to -20dB/decade for RC filter)

The high input impedance provided by an op amp circuit protects the instrument providing the signal from passing excessive current which could cause a voltage drop in the measurement signal or damage to the instrument itself.

Because the filter is second order, the rolloff after the cutoff frequency on a bode plot of a low pass filter for example, is -40 dB/decade as opposed to -20 dB/decade for a first order (RC) filter which means significantly greater attenuation outside the pass band and a sharper cutoff. This can be very useful if the noise frequency is close to the desired signal frequency.

[[Image:2ndOrderFilterDiagrams.gif]]

Where the cutoff frequency for both high and low pass filters in Hz is:

<math>f=1/(2*pi*sqrt(R_1 R_2 C_1 C_2))</math>

References:
http://en.wikipedia.org/wiki/Sallen_Key_filter

Second Order Active Filters

2008-12-09T00:03:44Z

StevenManuel:

2nd order active filtering has two main advantages:
* High impedance input, low impedance output
* greater attenuation at high range (-40dB/decade as opposed to -20dB/decade for RC filter)

The high input impedance provided by an op amp circuit protects the instrument providing the signal from passing excessive current which could cause a voltage drop in the measurement signal or damage to the instrument itself.

Because the filter is second order, the rolloff before/after the cutoff frequency or frequencies on a bode plot is -40 dB/decade as opposed to -20 dB/decade for a first order (RC) filter which means significantly greater attenuation outside the pass band and a sharper cutoff. This can be very useful if the noise frequency is close to the desired signal frequency.

[[Image:2ndOrderFilterDiagrams.gif]]

Where the cutoff frequency for both high and low pass filters in Hz is:

<math>f=1/(2*pi*sqrt(R_1 R_2 C_1 C_2))</math>

References:
http://en.wikipedia.org/wiki/Sallen_Key_filter

Second Order Active Filters

2008-12-09T00:03:10Z

StevenManuel:

2nd order active filtering has two main advantages:
* High impedance input, low impedance output
* greater attenuation at high range (-40dB/decade as opposed to -20dB/decade for RC filter)

The high impedance provided by an op amp circuit protects the instrument providing the signal from passing excessive current which could cause a voltage drop in the measurement signal or damage to the instrument itself.

Because the filter is second order, the rolloff before/after the cutoff frequency or frequencies on a bode plot is -40 dB/decade as opposed to -20 dB/decade for a first order (RC) filter which means significantly greater attenuation outside the pass band and a sharper cutoff. This can be very useful if the noise frequency is close to the desired signal frequency.

[[Image:2ndOrderFilterDiagrams.gif]]

Where the cutoff frequency for both high and low pass filters in Hz is:

<math>f=1/(2*pi*sqrt(R_1 R_2 C_1 C_2))</math>

References:
http://en.wikipedia.org/wiki/Sallen_Key_filter

Second Order Active Filters

2008-12-09T00:02:05Z

StevenManuel:

2nd order active filtering has two main advantages:
* High impedance input, low impedance output
* greater attenuation at high range (-40dB/decade as opposed to -20dB/decade for RC filter)

The high impedance provided by an op amp circuit protects the instrument providing the signal from passing excessive current which could cause a voltage drop in the measurement signal or damage to the instrument itself.

Because the filter is second order, the rolloff before/after the cutoff frequency or frequencies on a bode plot is -40 dB/decade as opposed to -20 dB/decade for a first order (RC) filter which means significantly greater attenuation outside the pass band and a sharper cutoff. This can be very useful if the noise frequency is close to the desired signal frequency.

[[Image:2ndOrderFilterDiagrams.gif]]

Where the cutoff frequency for both high and low pass filters in Hz is:

<math>f=1/(2*pi*sqrt(R_1 R_2 C_1 C_2))</math>

References:
http://en.wikipedia.org/wiki/Sallen_Key_filter

Second Order Active Filters

2008-12-09T00:00:57Z

StevenManuel:

2nd order active filtering has two main advantages:
* High impedance input, low impedance output
* greater attenuation at high range (-40dB/decade as opposed to -20dB/decade for RC filter)

The high impedance provided by an op amp circuit protects the instrument providing the signal from passing excessive current which could cause a voltage drop in the measurement signal or damage to the instrument itself.

Because the filter is second order, the rolloff before/after the cutoff frequency or frequencies on a bode plot is -40 dB/decade as opposed to -20 dB/decade for a first order (RC) filter which means significantly greater attenuation outside the pass band and a sharper cutoff. This can be very useful if the noise frequency is close to the desired signal frequency.

[[Image:2ndOrderFilterDiagrams.gif]]

Where the cutoff frequency for both high and low pass filters in Hz is:

<math>f=1/(2*pi*sqrt(R_1 R_2 C_1 C_2))</math>

Second Order Active Filters

2008-12-09T00:00:14Z

StevenManuel:

2nd order active filtering has two main advantages:
* High impedance input, low impedance output
* greater attenuation at high range (-40dB/decade as opposed to -20dB/decade for RC filter)

The high impedance provided by an op amp circuit protects the instrument providing the signal from passing excessive current which could cause a voltage drop in the measurement signal or damage to the instrument itself.

Because the filter is second order, the rolloff before/after the cutoff frequency or frequencies on a bode plot is -40 dB/decade as opposed to -20 dB/decade for a first order (RC) filter which means significantly greater attenuation outside the pass band and a sharper cutoff. This can be very useful if the noise frequency is close to the desired signal frequency.

[[Image:2ndOrderFilterDiagrams.gif]]

Where the cutoff frequency for both high and low pass filters in Hz is:

<math>f=1/(2 pi rt(R_1 R_2 C_1 C_2))</math>

Second Order Active Filters

2008-12-08T23:59:47Z

StevenManuel:

2nd order active filtering has two main advantages:
* High impedance input, low impedance output
* greater attenuation at high range (-40dB/decade as opposed to -20dB/decade for RC filter)

The high impedance provided by an op amp circuit protects the instrument providing the signal from passing excessive current which could cause a voltage drop in the measurement signal or damage to the instrument itself.

Because the filter is second order, the rolloff before/after the cutoff frequency or frequencies on a bode plot is -40 dB/decade as opposed to -20 dB/decade for a first order (RC) filter which means significantly greater attenuation outside the pass band and a sharper cutoff. This can be very useful if the noise frequency is close to the desired signal frequency.

[[Image:2ndOrderFilterDiagrams.gif]]

Where the cutoff frequency for both high and low pass filters in Hz is:

<math>f=1/(2pi*root(R_1 R_2 C_1 C_2))</math>

Second Order Active Filters

2008-12-08T23:59:07Z

StevenManuel:

2nd order active filtering has two main advantages:
* High impedance input, low impedance output
* greater attenuation at high range (-40dB/decade as opposed to -20dB/decade for RC filter)

The high impedance provided by an op amp circuit protects the instrument providing the signal from passing excessive current which could cause a voltage drop in the measurement signal or damage to the instrument itself.

Because the filter is second order, the rolloff before/after the cutoff frequency or frequencies on a bode plot is -40 dB/decade as opposed to -20 dB/decade for a first order (RC) filter which means significantly greater attenuation outside the pass band and a sharper cutoff. This can be very useful if the noise frequency is close to the desired signal frequency.

[[Image:2ndOrderFilterDiagrams.gif]]

Where the cutoff frequency for both high and low pass filters in Hz is:

<math>f=1/(2*pi*sqrt(R_1*R2*C1*C2))</math>

Second Order Active Filters

2008-12-08T23:58:36Z

StevenManuel:

2nd order active filtering has two main advantages:
* High impedance input, low impedance output
* greater attenuation at high range (-40dB/decade as opposed to -20dB/decade for RC filter)

The high impedance provided by an op amp circuit protects the instrument providing the signal from passing excessive current which could cause a voltage drop in the measurement signal or damage to the instrument itself.

Because the filter is second order, the rolloff before/after the cutoff frequency or frequencies on a bode plot is -40 dB/decade as opposed to -20 dB/decade for a first order (RC) filter which means significantly greater attenuation outside the pass band and a sharper cutoff. This can be very useful if the noise frequency is close to the desired signal frequency.

[[Image:2ndOrderFilterDiagrams.gif]]

Where the cutoff frequency for both high and low pass filters in Hz is:

<math>f=1/(2*pi*sqrt(R1*R2*C1*C2))</math>

Second Order Active Filters

2008-12-08T23:54:01Z

StevenManuel:

2nd order active filtering has two main advantages:
* High impedance input, low impedance output
* greater attenuation at high range (-40dB/decade as opposed to -20dB/decade for RC filter)

The high impedance provided by an op amp circuit protects the instrument providing the signal from passing excessive current which could cause a voltage drop in the measurement signal or damage to the instrument itself.

Because the filter is second order, the rolloff before/after the cutoff frequency or frequencies on a bode plot is -40 dB/decade as opposed to -20 dB/decade for a first order (RC) filter which means significantly greater attenuation outside the pass band and a sharper cutoff. This can be very useful if the noise frequency is close to the desired signal frequency.

[[Image:2ndOrderFilterDiagrams.gif]]

Where the cutoff frequencies in Hz are:

High Pass
<math>f=1/(2*pi*sqrt(R1*R2*C1*C2))</math>

Second Order Active Filters

2008-12-08T23:42:59Z

StevenManuel:

2nd order active filtering has two main advantages:
* High impedance input, low impedance output
* greater attenuation at high range (-40dB/decade as opposed to -20dB/decade for RC filter)

The high impedance provided by an op amp circuit protects the instrument providing the signal from passing excessive current which could cause a voltage drop in the measurement signal or damage to the instrument itself.

Because the filter is second order, the rolloff before/after the cutoff frequency or frequencies on a bode plot is -40 dB/decade as opposed to -20 dB/decade for a first order (RC) filter which means significantly greater attenuation outside the pass band and a sharper cutoff. This can be very useful if the noise frequency is close to the desired signal frequency.

[[Image:2ndOrderFilterDiagrams.gif]]

The transfer function

File:2ndOrderFilterDiagrams.gif

2008-12-08T23:42:15Z

StevenManuel: Active 2nd order high, low, and bandpass filter circuit diagrams

Active 2nd order high, low, and bandpass filter circuit diagrams

Second Order Active Filters

2008-12-08T23:40:56Z

StevenManuel:

2nd order active filtering has two main advantages:
* High impedance input, low impedance output
* greater attenuation at high range (-40dB/decade as opposed to -20dB/decade for RC filter)

The high impedance provided by an op amp circuit protects the instrument providing the signal from passing excessive current which could cause a voltage drop in the measurement signal or damage to the instrument itself.

Because the filter is second order, the rolloff before/after the cutoff frequency or frequencies on a bode plot is -40 dB/decade as opposed to -20 dB/decade for a first order (RC) filter which means significantly greater attenuation outside the pass band and a sharper cutoff. This can be very useful if the noise frequency is close to the desired signal frequency.

[[Image:Example.jpg]]

The transfer function

Second Order Active Filters

2008-12-08T23:34:41Z

StevenManuel:

2nd order active filtering has two main advantages:
*1) High impedance input, low impedance output
*2) greater attenuation at high range (-40dB/decade as opposed to -20dB/decade for RC filter)

The high impedance provided by an op amp circuit protects the instrument providing the signal from passing excessive current which could cause a voltage drop in the measurement signal or damage to the instrument itself.

Because the filter is second order, the rolloff before/after the cutoff frequency or frequencies on a bode plot is -40 dB/decade as opposed to -20 dB/decade for a first order (RC) filter which means significantly greater attenuation outside the pass band and a sharper cutoff which can be very useful if the noise frequency is close to the desired signal frequency.

Second Order Active Filters

2008-12-08T23:34:12Z

StevenManuel:

2nd order active filtering has two main advantages:
1) High impedance input, low impedance output
2) greater attenuation at high range (-40dB/decade as opposed to -20dB/decade for RC filter)

The high impedance provided by an op amp circuit protects the instrument providing the signal from passing excessive current which could cause a voltage drop in the measurement signal or damage to the instrument itself.

Because the filter is second order, the rolloff before/after the cutoff frequency or frequencies on a bode plot is -40 dB/decade as opposed to -20 dB/decade for a first order (RC) filter which means significantly greater attenuation outside the pass band and a sharper cutoff which can be very useful if the noise frequency is close to the desired signal frequency.

Category:Electronics

2008-12-08T23:32:50Z

StevenManuel:

*Analog
**[[Basic Linear Circuits Review]]
***[[Resistors (Ohm's Law), Capacitors, and Inductors]]
***[[Kirchhoff's Current and Voltage Laws]]
***[[Voltage and Current Dividers]]
***[[RC and RL Exponential Responses]]
***[[Passive Filters]]
***[[Second Order Active Filters]]
**[[Semiconductors]]
***[[Diodes and Transistors]]
***[[Operational Amplifiers (Op-Amps)]]

*[[Digital]]
**[[Logic Gates]]
**[[Flip-Flops and Latches]]
**[[555 Timer]]
**[[Schmitt Trigger]]

*[[Integrated Circuits]]

*Practical Considerations in Electrical Design
**[[Shielding, Grounding, Noise Suppression, etc.]]
**[[Conductors: stranded, solid, ribbon cable, coax, twisted pairs, wire gauge (thickness)]]
**[[Switch Debouncing]]

*Electrical Equipment and Software
**Power Supplies, Voltage Regulation, and Batteries
**[[Using Circuitmaker]]

Second Order Filters

2008-12-08T23:32:28Z

StevenManuel: Second Order Filters moved to Second Order Active Filters

#REDIRECT [[Second Order Active Filters]]

Second Order Active Filters

2008-12-08T23:32:28Z

StevenManuel: Second Order Filters moved to Second Order Active Filters

2nd order active filtering has two main advantages:
-High impedance input, low impedance output
-greater attenuation at high range (-40dB/decade as opposed to -20dB/decade for RC filter)

The high impedance provided by an op amp circuit protects the instrument providing the signal from passing excessive current which could cause a voltage drop in the measurement signal or damage to the instrument itself.

Because the filter is second order, the rolloff before/after the cutoff frequency or frequencies on a bode plot is -40 dB/decade as opposed to -20 dB/decade for a first order (RC) filter which means significantly greater attenuation outside the pass band and a sharper cutoff which can be very useful if the noise frequency is close to the desired signal frequency.

Second Order Active Filters

2008-12-08T23:32:12Z

StevenManuel:

Category:Electronics

2008-12-08T23:29:29Z

StevenManuel:

*Analog
**[[Basic Linear Circuits Review]]
***[[Resistors (Ohm's Law), Capacitors, and Inductors]]
***[[Kirchhoff's Current and Voltage Laws]]
***[[Voltage and Current Dividers]]
***[[RC and RL Exponential Responses]]
***[[Passive Filters]]
***[[Second Order Filters]]
**[[Semiconductors]]
***[[Diodes and Transistors]]
***[[Operational Amplifiers (Op-Amps)]]

*[[Digital]]
**[[Logic Gates]]
**[[Flip-Flops and Latches]]
**[[555 Timer]]
**[[Schmitt Trigger]]

*[[Integrated Circuits]]

*Practical Considerations in Electrical Design
**[[Shielding, Grounding, Noise Suppression, etc.]]
**[[Conductors: stranded, solid, ribbon cable, coax, twisted pairs, wire gauge (thickness)]]
**[[Switch Debouncing]]

*Electrical Equipment and Software
**Power Supplies, Voltage Regulation, and Batteries
**[[Using Circuitmaker]]

Category:Electronics

2008-12-08T23:27:34Z

StevenManuel:

*Analog
**[[Basic Linear Circuits Review]]
***[[Resistors (Ohm's Law), Capacitors, and Inductors]]
***[[Kirchhoff's Current and Voltage Laws]]
***[[Voltage and Current Dividers]]
***[[RC and RL Exponential Responses]]
***[[Passive Filters]]
***[[Active Filters]]
**[[Semiconductors]]
***[[Diodes and Transistors]]
***[[Operational Amplifiers (Op-Amps)]]

*[[Digital]]
**[[Logic Gates]]
**[[Flip-Flops and Latches]]
**[[555 Timer]]
**[[Schmitt Trigger]]

*[[Integrated Circuits]]

*Practical Considerations in Electrical Design
**[[Shielding, Grounding, Noise Suppression, etc.]]
**[[Conductors: stranded, solid, ribbon cable, coax, twisted pairs, wire gauge (thickness)]]
**[[Switch Debouncing]]

*Electrical Equipment and Software
**Power Supplies, Voltage Regulation, and Batteries
**[[Using Circuitmaker]]