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Operational amplifier are the basis for many circuit building blocks especially in the range of DC to 1 meg Hz. See [[OpAmp Links]]. | Operational amplifier are the basis for many circuit building blocks especially in the range of DC to 1 meg Hz. See [[OpAmp Links]]. | ||
− | == | + | == Page Status.... == |
( Some of schematics have been drawn in Eagle and the screen captured, use other methods if you wish. Feel free to add your own circuits, as long as they are basic building blocks, there are lots of other places for project circuits. If you get into more advanced circuits, give them their own page and link to them. Some entries are not complete, if the explanation of the circuit does not match the diagram that is a good tip off. ) | ( Some of schematics have been drawn in Eagle and the screen captured, use other methods if you wish. Feel free to add your own circuits, as long as they are basic building blocks, there are lots of other places for project circuits. If you get into more advanced circuits, give them their own page and link to them. Some entries are not complete, if the explanation of the circuit does not match the diagram that is a good tip off. ) | ||
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More circuits that would be good to add | More circuits that would be good to add | ||
+ | *Constant Current Circuit | ||
+ | *Wheatstone Bridge | ||
+ | [http://itp.nyu.edu/physcomp/sensors/Schematics/WheatstoneBridge Wheatstone Bridge] | ||
*AC Coupling Capacitor / High Pass Filter | *AC Coupling Capacitor / High Pass Filter | ||
*Battery Lamp and Switch | *Battery Lamp and Switch | ||
*Diode Rectifier | *Diode Rectifier | ||
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*LM35 Temperature Sensor | *LM35 Temperature Sensor | ||
*555 Timer astable oscillator | *555 Timer astable oscillator | ||
− | * | + | *diode for forward drop bias voltage |
− | * | + | *row and collumn connection |
*charge pump | *charge pump | ||
− | * | + | *transformer |
+ | *voltage multiplier | ||
*diode logical or | *diode logical or | ||
+ | *RC timer | ||
+ | *diode full wave bridge | ||
*H Bridge | *H Bridge | ||
− | An H bridge is an electronic circuit that causes current to flow in one direction or the other ( from a | + | An H bridge is an electronic circuit that causes current to flow in one direction or the other ( from a singel ended power supply ). Often used for motor control [[motor driver]]. |
It is an electronic double pole double throw switch. | It is an electronic double pole double throw switch. | ||
− | + | [http://code.rancidbacon.com/ElectronicsElectronics] See Section on ''H-Bridge'' | |
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− | + | *Simple Oscillator circuits | |
− | * | + | *Current mirrors |
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*RF Mixers | *RF Mixers | ||
− | * | + | *Transistor Darlington Connection |
− | * | + | *Trasistor Sislac ( sp ) Connection |
− | * | + | *Tranistor Current Mirror |
− | * | + | *Transistor Current Limit, Constant Current. |
− | + | *[[Colpitts Oscillator]] | |
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<!---------------------------------------------------------------------> | <!---------------------------------------------------------------------> | ||
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== Current Sense Resistor ( Shunt Resistance ) == | == Current Sense Resistor ( Shunt Resistance ) == | ||
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Where | Where | ||
*R shunt resistor used to sense the current ( and divert it from the meter ). Usually much less in value than the internal resistance of the meter. | *R shunt resistor used to sense the current ( and divert it from the meter ). Usually much less in value than the internal resistance of the meter. | ||
− | *METER meter or other device used to measure the voltage across the shunt | + | *METER meter or other device used to measure the voltage across the shunt reistor. Often the resistance of the meter is ignored ( if high ). |
*BATTERY a battery or other voltage source. | *BATTERY a battery or other voltage source. | ||
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Discussion: | Discussion: | ||
− | In the old days a sensitive meter, say 50 mv full scale, would be used with a set of shunt, some looking like metal bars, to measure a wide range of currents, up to and exceeding 50 amps | + | In the old days a sensitive meter, say 50 mv full scale, would be used with a set of shunt, some looking like metal bars, to measure a wide range of currents, up to and exceeding 50 amps. |
− | + | More information: | |
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#[http://www.scienceshareware.com/bg-current-monitoring.htm Scienceshareware.com's How A Precision Resistor Is Used to Measure / Calculate Current and Power in an Electrical Circuit.] | #[http://www.scienceshareware.com/bg-current-monitoring.htm Scienceshareware.com's How A Precision Resistor Is Used to Measure / Calculate Current and Power in an Electrical Circuit.] | ||
#[http://www.maxim-ic.com/appnotes.cfm/appnote_number/746/ High-Side Current-Sense Measurement: Circuits and Principles] | #[http://www.maxim-ic.com/appnotes.cfm/appnote_number/746/ High-Side Current-Sense Measurement: Circuits and Principles] | ||
#[http://en.wikipedia.org/wiki/Shunt_(electrical) Shunt (electrical) From Wikipedia, the free encyclopedia] | #[http://en.wikipedia.org/wiki/Shunt_(electrical) Shunt (electrical) From Wikipedia, the free encyclopedia] | ||
* Other ways to measure current: [[Motor_driver#current_sense]] | * Other ways to measure current: [[Motor_driver#current_sense]] | ||
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== Filter Capacitor / Decoupling Capacitor / Low Pass Filter == | == Filter Capacitor / Decoupling Capacitor / Low Pass Filter == | ||
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In this circuit C1 is a classic filter capacitor it charges while the diode conducts, it discharges and supplies current when the diode does not. R and C2 are a second stage filter. With R set to 0, it simply adds to the value of C1. With R in the circuit it forms a low pass filter which helps remove the ripple from the power ( at the cost of some voltage drop ). In the old days R would often be a low value inductor which had a similar effect without the voltage drop. A capacitor alone is often put across a circuit component that uses power to supply bursts of current and stop noise from being propagated through the power supply. | In this circuit C1 is a classic filter capacitor it charges while the diode conducts, it discharges and supplies current when the diode does not. R and C2 are a second stage filter. With R set to 0, it simply adds to the value of C1. With R in the circuit it forms a low pass filter which helps remove the ripple from the power ( at the cost of some voltage drop ). In the old days R would often be a low value inductor which had a similar effect without the voltage drop. A capacitor alone is often put across a circuit component that uses power to supply bursts of current and stop noise from being propagated through the power supply. | ||
− | + | More Information: | |
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<!---------------------------------------------------------------------> | <!---------------------------------------------------------------------> | ||
− | + | == Op amp Non Inverting Amplifier == | |
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− | == Op | ||
Use this circuit where the signal you have is not as large as you want, or cannot provide enough current. It is called non inverting because a positive input produces a positive output ( An inverting amplifier produces a negative output when given a positive input ). | Use this circuit where the signal you have is not as large as you want, or cannot provide enough current. It is called non inverting because a positive input produces a positive output ( An inverting amplifier produces a negative output when given a positive input ). | ||
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More Information: | More Information: | ||
− | * | + | *[OpAmp Links] |
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<!---------------------------------------------------------------------> | <!---------------------------------------------------------------------> | ||
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Use this circuit when you have a signal of high impedance ( can supply only a little current ) that you want to connect to another circuit that draws a significant current ( up to about 10 ma for the typical op amp. ). For example if you wish to measure the output of a voltage divider with a 0 to 1 ma meter a unity gain buffer might be just what you need. This circuit is also know as a voltage follower. | Use this circuit when you have a signal of high impedance ( can supply only a little current ) that you want to connect to another circuit that draws a significant current ( up to about 10 ma for the typical op amp. ). For example if you wish to measure the output of a voltage divider with a 0 to 1 ma meter a unity gain buffer might be just what you need. This circuit is also know as a voltage follower. | ||
− | The unity gain buffer has an output voltage just the same as the input voltage. The advantage is that the input circuit does not “feel” the output. That is the input acts pretty much like a very large resistor ( many mega ohms or more ) connected to ground, and the output | + | The unity gain buffer has an output voltage just the same as the input voltage. The advantage is that the input circuit does not “feel” the output. That is the input acts pretty much like a very large resistor ( many mega ohms or more ) connected to ground, and the output supply's whatever current ( up to about 10 ma ) is necessary to maintain the output voltage. Here is the circuit: |
Circuit: | Circuit: | ||
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Discussion: | Discussion: | ||
The values of RIN and RFB are not very critical and are normally 0 ohms, just a straight connection. The op amp here is a quad or 4 op amp part, we are using just one section of it. Power needs to be supplied to pin 8 and 4 in the usual way for op amps. | The values of RIN and RFB are not very critical and are normally 0 ohms, just a straight connection. The op amp here is a quad or 4 op amp part, we are using just one section of it. Power needs to be supplied to pin 8 and 4 in the usual way for op amps. | ||
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More information: | More information: | ||
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Discussion: | Discussion: | ||
− | I you have a lot of components that use the same voltage put them in parallel. This is how most lights in a house are wired. Each individual light can be turned on and off without changing the current or voltage in the other lights. With a bit of math you can show that the two resistors act like one resistor of value R = | + | I you have a lot of components that use the same voltage put them in parallel. This is how most lights in a house are wired. Each individual light can be turned on and off without changing the current or voltage in the other lights. With a bit of math you can show that the two resistors act like one resistor of value R = R1 + R2 /( R1 * R2 ). When you need a resistor of a different value than you have you can sometimes “make it up” using a parallel connection of resistors you do have. Two identical resistors in parallel are equivalent to one of half the resistance. A parallel circuit can have more than 2 resistors, there can be 3, 4, ... You can find out more about parallel circuits in the references. This circuit should be contrasted with the Series Circuit. Parallel circuits can also be used with other components, the equations vary, for capicators the capacitances add in a parallel circuit. |
More information: | More information: | ||
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Use this circuit when you want to feed a user input to a digital circuit, for example a PIC input pin. | Use this circuit when you want to feed a user input to a digital circuit, for example a PIC input pin. | ||
− | A pull up is a fairly high value resistor (say 1 to 100 K ohms) that is connected to the positive side of the power supply. This makes the other end of the resistor the same voltage as the power supply (as long as it is connected to a high impedance). The other end of the resistor is connected to a switch that is then connected to ground. When the switch is connected current flow through the resistor drops the entire power supply voltage and the input voltage for the circuit is now 0 (sometimes called active low, since when the switch is active the output is low) | + | A pull up is a fairly high value resistor (say 1 to 100 K ohms) that is connected to the positive side of the power supply. This makes the other end of the resistor the same voltage as the power supply (as long as it is connected to a high impedance). The other end of the resistor is connected to a switch that is then connected to ground. When the switch is connected current flow through the resistor drops the entire power supply voltage and the input voltage for the circuit is now 0 (sometimes called active low, since when the switch is active the output is low). Pull up is sometimes used without the switch to keep a signal high all the time. |
Circuit: | Circuit: | ||
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*[http://www.seattlerobotics.org/encoder/mar97/basics.html Very Basic Circuits] | *[http://www.seattlerobotics.org/encoder/mar97/basics.html Very Basic Circuits] | ||
*[http://www.dnatechindia.com/index.php/Tutorials/8051-Tutorial/Switch-Interfacing.html Interfacing Switch to Microcontroller] | *[http://www.dnatechindia.com/index.php/Tutorials/8051-Tutorial/Switch-Interfacing.html Interfacing Switch to Microcontroller] | ||
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Debouncing Discussion: | Debouncing Discussion: | ||
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Discussion: | Discussion: | ||
Just a variation on the Pull Up and Switch. | Just a variation on the Pull Up and Switch. | ||
+ | <!---------------------------------------------------------------------> | ||
− | + | == Series Circuit == | |
− | + | In a series circuit the current first flows through one component then another and so on. The key to these circuits is that the current is the same in every element of the circuit and the total of the voltage across each of the components adds up to the voltage of the battery. A current meter is always in series with the part of the circuit whose current is being measured. | |
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− | + | Circuit: | |
+ | [[Image:series.png | Series Circuit ]] | ||
− | + | Where | |
− | + | *R1 resistor 1 or any other 2 terminal component, capacitor, inductor, diode.... | |
+ | *R2 resistor 2 or any other 2 terminal component..... | ||
+ | *BAT a battery or other voltage source | ||
− | + | I you have a lot of components that use the same current put them in series. This is often how LEDs are connected to higher voltages; this also eliminates the need for a current limiting resistor on each LED. With a bit of math you can show that the two resistors act like one resistor of value R = R1 + R2 . When you need a resistor of a different value than you have you can sometimes “make it up” using a series connection of resistors you do have. Two identical resistors in series are equivalent to one of double the resistance. A series circuit can have more than 2 resistors, there can be 3, 4, ... You can find out more about series circuits in the references. This circuit should be contrasted with the Parallel Circuit. A voltage divider is an example of a series circuit. | |
− | + | More information: | |
− | + | * [http://en.wikipedia.org/wiki/Parallel_circuit Series and parallel circuits From Wikipedia, the free encyclopedia] | |
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<!---------------------------------------------------------------------> | <!---------------------------------------------------------------------> | ||
− | == | + | == Three Terminal Regulator == |
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− | Use | + | Use when you need a regulated voltage and or short circuit protection. |
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− | + | Most circuits run better if the primary power source is a constant fixed voltage. A battery is only a poor approximation to this. Taking a battery or other voltage source ( like a wall wart plug in transformer ) and running it through a voltage regulator transforms it into a good fixed source of voltage. It also generally adds current limiting as short circuit protection. The 7805 is a very common 5 volt regulator. | |
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+ | Circuit: | ||
+ | [[Image:ttr.png | Three Terminal Regulator ]] | ||
− | + | Discussion: | |
− | + | The circuit above is very basic. Practical circuits normally include filter capacitors on both the input and the output. Most regulators protect against both over temperature and over current. Regulators come in various voltages both positive and negative. They also vary in maximum current output. There are also adjustable regulators, ways of using regular regulators as adjustable ones, and ways of boosting the current output. The spec sheets often describe how to do these things. Voltage regulators “use up” a couple of volts of the input voltage, low drop out regulators have use less, cost more. It is a good idea to check the specification for any regulator you are going to use. The LM78xx ( positive ) and LM79xx ( negative ) are quite common. | |
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− | + | More information: | |
− | + | *[[Basic Voltage Regulators]] | |
+ | *[http://en.wikipedia.org/wiki/7805 7805 From Wikipedia, the free encyclopedia] | ||
+ | *[http://www.tkk.fi/Misc/Electronics/circuits/psu_5v.html Simple 5V power supply for digital circuits] | ||
== Relay with Diode Snubber == | == Relay with Diode Snubber == | ||
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Discussion: | Discussion: | ||
− | + | In the circuit shown, the "input" will come directly from the small current source device (microcontroller output pin). The resistor must be sized correctly, along with the NPN transistor DC current gain, to ensure sufficient current passes through the relay coil to activate it. | |
Other inductors that might use a diode snubber are transformers, solenoids, dc motors, and of course straight ahead inductors. | Other inductors that might use a diode snubber are transformers, solenoids, dc motors, and of course straight ahead inductors. | ||
− | More information: | + | More information: |
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*[http://en.wikipedia.org/wiki/snubber "snubber" from Wikipedia, the free encyclopedia] | *[http://en.wikipedia.org/wiki/snubber "snubber" from Wikipedia, the free encyclopedia] | ||
*[http://en.wikipedia.org/wiki/flyback_diode "flyback diode" from Wikipedia, the free encyclopedia] | *[http://en.wikipedia.org/wiki/flyback_diode "flyback diode" from Wikipedia, the free encyclopedia] | ||
*[http://en.wikipedia.org/wiki/Relay "relay" from Wikipedia, the free encyclopedia] | *[http://en.wikipedia.org/wiki/Relay "relay" from Wikipedia, the free encyclopedia] | ||
*[http://www.dnatechindia.com/index.php/Tutorials/8051-Tutorial/Relay-Interfacing.html Microcontroller] relay interfacing example. | *[http://www.dnatechindia.com/index.php/Tutorials/8051-Tutorial/Relay-Interfacing.html Microcontroller] relay interfacing example. | ||
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== Transistor Low Side Switch == | == Transistor Low Side Switch == | ||
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A low side switch is one which switches a circuit on and off at the ground or low side of the circuit. The advantage of a low side switch is that when using a transistor as the switch the voltage to drive the transistor is itself a low voltage. It is often the easy way to drive LEDS, motors, and other high current devices from such low power devices as PIC output ports. Low side switches are popular and there are many integrated circuits for them as well as this circuit. | A low side switch is one which switches a circuit on and off at the ground or low side of the circuit. The advantage of a low side switch is that when using a transistor as the switch the voltage to drive the transistor is itself a low voltage. It is often the easy way to drive LEDS, motors, and other high current devices from such low power devices as PIC output ports. Low side switches are popular and there are many integrated circuits for them as well as this circuit. | ||
− | Circuit | + | Circuit: |
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[[Image:Tran_lss.jpg | Transistor Low Side Switch ]] | [[Image:Tran_lss.jpg | Transistor Low Side Switch ]] | ||
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*Compute the value of R_LED using ohms law and the specifications for the LED. | *Compute the value of R_LED using ohms law and the specifications for the LED. | ||
*Compute the current through the LED. | *Compute the current through the LED. | ||
− | *The transistor must | + | *The transistor must supply the current, it should be equal approxtely to the input voltage divided by R1 times the beta of the transistor. |
An example calculation would be nice, and will appear later. | An example calculation would be nice, and will appear later. | ||
− | This circuit is sometimes called "grounded-emitter configuration". | + | This circuit is sometimes called "grounded-emitter configuration". |
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More Information: | More Information: | ||
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== Transistor High Side Switch == | == Transistor High Side Switch == | ||
− | Use this circuit when you wish to turn a load on and off with a voltage at a low current. Note that low side of the load is grounded. The voltage to turn on the switch is equal to the supply voltage ( or perhaps just a bit larger ) | + | Use this circuit when you wish to turn a load on and off with a voltage at a low current. Note that low side of the load is grounded. The voltage to turn on the switch is equal to the supply voltage ( or perhaps just a bit larger ) |
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− | + | A high side switch is one which switches a circuit on and off at the supply voltage or high side of the circuit. The advantage of a high side switch is that the load is grounded on one side. Compared to the low side switch it needs a higher voltage to drive it, but it also eliminates one resistor of that circuit. It the voltage to drive it is available it may be the circuit of choice. It is often the easy way to drive leds motors and other high current devices from such low power devices as PIC output ports. | |
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Circuit: | Circuit: | ||
− | + | [[Image:tran_hss.png | Transistor High Side Switch ]] | |
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− | [[Image:tran_hss.png | Transistor High Side Switch]] | ||
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Where | Where | ||
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No resistor is needed into the base of the transistor because as the load draws current the voltage at the base will rise and limit the base current. The input voltage should be about equal to VPLUS_VDD, high compared to that needed for the low side switch. | No resistor is needed into the base of the transistor because as the load draws current the voltage at the base will rise and limit the base current. The input voltage should be about equal to VPLUS_VDD, high compared to that needed for the low side switch. | ||
− | This high side switch usually requires the base voltage of Q to be VPLUS_VDD plus the turn-on voltage of the transistor to turn all the way on. Another approach to the high side switch that requires a lower turn-on voltage is to use a PNP transistor as the switch. The base of the PNP is pulled up to VPLUS_VDD and connected to the collector of a small signal NPN transistor, Q2. Q2's emitter is connected to ground and its base is connected to the input signal through a current limiting resistor | + | This high side switch usually requires the base voltage of Q to be VPLUS_VDD plus the turn-on voltage of the transistor to turn all the way on. Another approach to the high side switch that requires a lower turn-on voltage is to use a PNP transistor as the switch. The base of the PNP is pulled up to VPLUS_VDD and connected to the collector of a small signal NPN transistor, Q2. Q2's emitter is connected to ground and its base is connected to the input signal through a current limiting resistor. |
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== Transistor Emitter Follower == | == Transistor Emitter Follower == | ||
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*R_LOAD represents the resistance of the load | *R_LOAD represents the resistance of the load | ||
*Q is a npn bipolar transistor | *Q is a npn bipolar transistor | ||
− | *VPLUS_VDD is the power supply for the | + | *VPLUS_VDD is the power supply for the LED |
The current to drive the circuit is approximately the current to drive the load divided by the beta of the transistor. Use a Darlington connected transistor for a very high beta. | The current to drive the circuit is approximately the current to drive the load divided by the beta of the transistor. Use a Darlington connected transistor for a very high beta. | ||
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*[http://en.wikipedia.org/wiki/Common_collector Common collector From Wikipedia, the free encyclopedia] | *[http://en.wikipedia.org/wiki/Common_collector Common collector From Wikipedia, the free encyclopedia] | ||
+ | |||
+ | == Voltage Divider == | ||
+ | Voltage Divider | ||
+ | |||
+ | We use a voltage divider when we have a voltage that is too big and we just want a fraction ( like 1/3 or .33 ) of it. It is like an amplifier with a gain of less than 1. We use two resistors, the output is always a constant fraction of the input voltage. | ||
+ | |||
+ | Sometimes we use a potentiometer as a voltage divider. This makes the ratio of output to input adjustable. This is how we make a gain control or volume control. | ||
+ | |||
+ | Circuit: | ||
+ | [[Image:vdivide.png | Voltage Divider ]] | ||
+ | |||
+ | Where | ||
+ | *R1 resistor 1 | ||
+ | *R2 resistor 2 | ||
+ | *POT a potentiometer | ||
+ | |||
+ | The ratio of input to output is: output/input = R2/( R1 + R2 ). | ||
+ | |||
+ | Discussion | ||
+ | |||
+ | The equation assumes that the input source is low impedance and the output is high impedance, if this is not true consider using a buffer on the input or the output ( Op Amp Unity Gain Buffer or Transistor Emitter Follower ) For audio applications a so called “log taper” pot may be used as it better matches the way in which we hear. If you want a calibrated control you may use a precision “10 turn precision” pot. | ||
+ | |||
+ | More information: | ||
+ | *[http://www.seattlerobotics.org/encoder/mar97/basics.html Very Basic Circuits] | ||
+ | *[http://itp.nyu.edu/physcomp/sensors/Schematics/VoltageDivider Voltage Divider] | ||
+ | |||
+ | == RC Filter == | ||
+ | |||
+ | The most basic filters are the RC-High Pass and RC-Low Pass filters. The high pass filter removes DC and low frequencies and the low pass removes high frequencies. | ||
+ | |||
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+ | '''High Pass''' [[Image:rchighpass.png | RC High Pass Filter]] | ||
+ | '''Low Pass''' [[Image:rclowpass.png | RC Low Pass Filter]] | ||
+ | |||
+ | Both circuits have the same 3dB frequency or the frequency at which the power of the signal is aproximately halved. | ||
+ | |||
+ | <math> | ||
+ | f_\mathrm{c} = {1 \over 2 \pi \tau } = {1 \over 2 \pi R C} | ||
+ | </math> | ||
+ | |||
+ | The way to remember the two circuits is to think about how the capacitor acts at various signal frequencies. At high frequencies capacitors act like wires. At low frequencies capacitors act like disconnections. | ||
+ | |||
+ | An important use of low pass filters is for the anti-aliasing circuity on the input of an A/D converter or the output of a D/A converter. An important use of a high pass filter is to remove the DC offset of a signal. For example, it's possible to use a power supply that is +5 to GND to generate a sin from a D/A converter and use a high pass filter to change the sin to a +2.5 to -2.5 signal at the output. | ||
+ | |||
+ | More information: | ||
+ | *[http://en.wikipedia.org/wiki/Low-pass_filter Low Pass Filter] | ||
+ | *[http://en.wikipedia.org/wiki/High-pass_filter High Pass Filter] | ||
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+ | == Light Emitting Diode ( with current limiting resistor ) == | ||
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+ | Use this circuit to light low power LEDs | ||
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+ | A light emitting diode can be very sensitive to small voltage changes, just a bit too much voltage and the LED will draw too much current and “burn out”. Thus it is often used with a resistor in series. If we have a 5 volt source of voltage and an LED that is specified for 2.5 volts at 10 ma, then the resistor must have ( 5 – 2.5 ) volts = 2.5 volts and 10 ma. Using ohms law 2.5/10 x 10 ee-3 = 250 ohms. | ||
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+ | A transistor low or high side switch can be used with the resistor if your input cannot supply enough current for the LED. | ||
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+ | Circuit: | ||
+ | [[Image:ledres.jpg | LED and current limiting resistor ]] | ||
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+ | Where | ||
+ | *LED the LED | ||
+ | *R_LED the current limiting resistor | ||
+ | *INPUT voltage source for lighting the LED | ||
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+ | More information: | ||
+ | *[http://www.seattlerobotics.org/encoder/mar97/basics.html Very Basic Circuits ] | ||
+ | *[http://www.iguanalabs.com/1stled.htm Learning About Transistors and LEDs ] | ||
+ | *[http://quantsuff.com/index.htm WELCOME TO QUANTSUFF'S CIRCUIT PAGE. Low Voltage, high-efficiency Drivers for LED Lights ] | ||
+ | *[http://www.dnatechindia.com/index.php/Tutorials/8051-Tutorial/LED-Interfacing.html Interfacing LED to 8051 Microcontroller] | ||
== Transistor -- Push Pull Circuit == | == Transistor -- Push Pull Circuit == | ||
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Often Q1 is a high gain small signal transistor and Q2 a lower gain power transistor. You can use PNP transistors by using a negative power supply. Use a ULN2803 ( or similar chips ) to get 8 darlingtons in one package, useful as low side switches and in conjunction with microcontrollers. | Often Q1 is a high gain small signal transistor and Q2 a lower gain power transistor. You can use PNP transistors by using a negative power supply. Use a ULN2803 ( or similar chips ) to get 8 darlingtons in one package, useful as low side switches and in conjunction with microcontrollers. | ||
− | * The above diagram shows a | + | * The above diagram shows a low side switch, but other transistor configurations can also be used. |
* PNP transistors can also be used, the important point is that both transistors be of the same type. | * PNP transistors can also be used, the important point is that both transistors be of the same type. | ||
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*[http://en.wikipedia.org/wiki/Sziklai_pair Sziklai pair From Wikipedia, the free encyclopedia] | *[http://en.wikipedia.org/wiki/Sziklai_pair Sziklai pair From Wikipedia, the free encyclopedia] | ||
+ | == Schmitt Trigger == | ||
+ | Use this circuit when you want to sense if an input is either high or low. The circuit elmininate inputs that are "in between" and stops small noise signals from causing the input to rapildy oscillating from high to low. | ||
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Circuit: | Circuit: | ||
− | [[Image: | + | [[Image:opamp_st.png | Schmitt Trigger ]] |
Where | Where | ||
− | * | + | *RIN input resistor -- when this inputs more current than the positive feedback resistor the output switches to the voltage at the input, else it stays at the output voltage it has already reached. Typically lower in value than RFB. |
− | * | + | *RFB positive feedback resistor the output voltage is feed back to the input and keeps the output at its current voltage. |
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− | + | Discussion: | |
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− | + | The circuit is used to switch between two states even in the presence of noise. This is an somewhat unusual op amp circuit as it uses positive not negative feedback. See the references for a better explanation and variations on the circuit. | |
+ | Schmidt Triggers are also available as integrated circuits which require no external components. | ||
− | + | More Information: | |
− | + | *[[OpAmp Links]] | |
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== Oscillators == | == Oscillators == | ||
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== Power up low active reset circuit == | == Power up low active reset circuit == | ||
− | Use this circuit with a microcontroller to keep it in reset for a short period of time after the power supply is | + | Use this circuit with a microcontroller to keep it in reset for a short period of time after the power supply is tuned on. Some microcontrolles like this kind of start up. Note that this is really just an application of the RC Filter, also on this page. |
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== ADC Voltage Protection Circuit == | == ADC Voltage Protection Circuit == | ||
− | The input to an Analog to Digital Converter (ADC) has some issues that need a bit of attention. | + | The input to an Analog to Digital Converter (ADC) has some issues that need a bit of attention. One is that the input is normally quite sensitive to input voltages that are too high or too low. This circuit protects the ADC. ( Additionally it can provide amplification and a low impedance input to the ADC which can be quite helpful ) Note this is a specialization of '''Op amp Non Inverting Amplifier''' also on this page. |
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− | (Additionally | ||
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[[Image:Adc.png|thumb|800px|center]] | [[Image:Adc.png|thumb|800px|center]] | ||
− | * | + | *The opamp circuit is used to |
#provide a low input source resistance to the ADC | #provide a low input source resistance to the ADC | ||
− | #protect ADC | + | #protect ADC whose input signal may exceed the supply/reference voltage (i.e. INPUT > V<sub>cc</sub>) |
+ | *In scenario 2, the voltage into the ADC input pin is capped at the supply voltage. | ||
*Requirement for the op-amp: | *Requirement for the op-amp: | ||
**The op-amp can withstand the input signal beyond the supply voltage, provided that the input current is limited to I<sub>max</sub> (e.g. [http://focus.ti.com/lit/ds/symlink/opa4340.pdf OPA4340] I<sub>max</sub> = 10mA) | **The op-amp can withstand the input signal beyond the supply voltage, provided that the input current is limited to I<sub>max</sub> (e.g. [http://focus.ti.com/lit/ds/symlink/opa4340.pdf OPA4340] I<sub>max</sub> = 10mA) | ||
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More Information: | More Information: | ||
* [[input protection]] circuits | * [[input protection]] circuits | ||
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+ | ==Seven segment LEDs== | ||
+ | Use these to display number to a user. | ||
− | + | *[http://chungyan5.no-ip.org/vc/trunk/AltiumDesigner6ProjectFiles.zip?root=7segment_LEDs&view=log AltiumDesigner6ProjectFiles] | |
− | + | *[http://www.dnatechindia.com/index.php/Tutorials/8051-Tutorial/7-Seg-Interfacing.html Interfacing Seven Segment to Microcontroller] | |
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== Further Reading == | == Further Reading == | ||
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''... do we need another page for not-so-basic circuits such as the Baker clamp ? ...'' I looked it up and would say it is not so basic. So perhaps [[Not So Basic Circuits]] would be a good place to put such things. What do others think? russ_hensel | ''... do we need another page for not-so-basic circuits such as the Baker clamp ? ...'' I looked it up and would say it is not so basic. So perhaps [[Not So Basic Circuits]] would be a good place to put such things. What do others think? russ_hensel | ||
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[[Category:Components]][[Category:Schematics]] | [[Category:Components]][[Category:Schematics]] |