Draw a scheme with a resistor and a push button switch to reset a microcontroller. Consider a time constant of 20 ms (the time required to reach 63% of the maximum voltage) for a resistor of 100 Kohms. Calculate the capacitor required.
In scheme 1 the signal is normally at high (3 volts) and goes to zero volts when the push button key is pressed (RESET AT LOW)
In scheme 2 the signal is normally at zero volts and goes to 3 volts when the push button key is pressed. (RESET AT HIGH)
Draw a scheme with an ON-OFF switch (without central pole) that will indicate to the microcontroller that when in position A, that pin will be at zero volts (LOW) and when in position B it will be at 3 volts (HIGH).
On the other hand, the capacitor blocks DC signals (or very low frequency signals)
Vin = AC Signal –> f = 1 MHz C = 1 uFarad Xc = 1 / (2 π f C) Xc = 1/ (2 x 3.14 x 1 x 10 6 x 1 x 10 -6 ) Xc = 1/ (2x3.14) ohms Xc = 0.16 ohms Xc = ALMOST A SHORT CIRCUIT ! THUS, An AC signal can “cross” (or be propagated across) a capacitor, provided the frequency of the AC signal is high enough to make the capacitor impedance very low. C Xc Vin Vout R1 R2 + 5V 0 4V 0 2V
When there is no AC Voltage, The DC Voltage of the Battery is Converted to AC Voltage to feed the Computer
A computer normally needs a Stabilizer and a No-Break.
Guarantee that AC Voltage Supplied to a Computer is kept within Certain Limits to Avoid Damaging the Computer
Common computer No-Breaks do not generate electricity from the battery when there is external power. They just generate electricity when there is no external power. Therefore, if the external power varies its amplitude considerably, it is not good for the computer. Due to this, a stabilizer is needed before the No-Break.
Two Equipments(circuits) can communicate either using commom mode signals or differential signals. The most common are common mode signals. In this case a common reference wire is established and voltages are related to that common wire, which is usually termed Ground wire.
Safety ground is a wire employed to connect metalic parts of the equipment to the earth´s ground. This is done to prevent accidents by persons touching metalic parts with voltage levels (due to defective parts)
Comes from the street transformer (where is earth grounded) but can not be used for safety ground. A separate safety ground is required.
Equip. A Equip. B Common (ground) Signals Equip. A Equip. B Common (ground) Signals Safety Ground Neutral Hot Wire Safety ground
Used to allow current in just one direction, to rectify AC waveforms. When current flows in the correct direction, voltage drop across it is approximately 0.65V, almost independently of the current. When voltage is reversed, it acts like an enormous resistor. A LED is also a diode but the voltage drop across its terminals is usually 1.5 Volts, instead of 0.65 Volts.
Used to establish a certain reference voltage in a circuit section, almost independently of the reverse current flow across it. Reverse voltage depends on the type of zener diode. (direct voltage drop is 0.65 V)
Common LEDs (Light Emmitting Diodes) can be turned “ON” with a current between 5mA and 10mA.
Microcontrollers Can Have Currents in Output pins between 2mA and 20ma when in “LOW” Level (IO L ) and currents between 2mA and 10mA when in “HIGH” level (IO H ). Note that when the output pin of the microcontroller is at 0 volts level the current flows into the pin and when it is at 3 volts, the current flows out of the pin.
In order to protect the Microcontroller to not exceed its output current and also to protect the LED to not exceed the current across its terminals, a resistor in series with the LED is used.
Draw a scheme to connect a LED to an output pin of a microcontroller, turning the LED “ON” when the output pin is at logic “0” and turning it “ON” when the output pin is at logic “1”.
Calculate the resistor to limit the current across the LED to 5 mA. Consider that the power supply is 3 Volts. Remember that there is a voltage drop across the LED when the current is flowing in the correct direction.
Ohm’s Law Kirchoff’s Voltage Law – The algebraic sum of all voltage rises and voltage drops around a closed loop must equal zero Kirchoff’s Current Law – The algebraic sum of all currents entering and leaving a node must equal zero Series Equivalent Parallel Equivalent Remember:
First, determine the number of closed loops and then draw the direction of the currents around the loops.
Second, identify the plus and minus voltage on each resistor, according to the currents flowing across them.
Third, traverse the loop associating a plus or minus sign, depending on the the entrance sign, when traversing the loop.
20V 100 100 300 200 500 I1 I2 I3 R1 R4 R5 R3 R2
Thevenin´s Theorem Thevenin´s Theorem: Any two terminal circuit can be replaced by a resistance, equal to the resistance measured across the two terminals, in series with a voltage source, equal to the open circuit voltage accross the two terminals. What For ??: => The Key objective is to find a simple circuit that is equivalent to a more complex one. For example: Obtain an equivalent circuit between terminals A and B that is simpler than the circuit on the right: Step1 : Find Vth . Because the terminals are open, there will be no current flowing through the 4 ohms resistor, and therefore, no voltage drop accross it. So, the open circuit voltage (Vth) will be equal the voltage across the 10 resistor. Thus, by the voltage divider rule: Vth = 10V. Step2 : Find Rth (the resistance seen looking into terminals A and B). Replacing the voltage source with its ideal internal resistance (zero ohms), we find that: Rth = 4 + 15 // 2 = 10 25V 15 4 2 A B Vth Rth A B 15 4 2 A B Rth 10V 10 A B
TRANSITOR - PNP Emitter Base Collector Current
Bipolar Transistor -PNP n n p p Emitter Base Collector Ie = Ic + Ib Emitter Base Collector Current
Bipolar Transistor - NPN Emitter Base Collector Emitter Base Collector Ie = Ic + Ib p p n n
Cut-Off Region – When Ic is almost zero and the absolute value of the Base-Emitter voltage is lower than 0.65 V (for silicon transistors). When the transistor reaches this region, the equations above are no longer valid .
Saturation Region – When Vce is almost zero and the absolute value of the Base-Emitter voltage is larger than 0,65 V (for silicon transistors). When the transistor reaches this region, the equations above are no longer valid.
When the input signal is large enough, the transistor can be driven into saturation & cutoff which will make the transistor act as an electronic switch.
Saturation - The region of transistor operation where a further increase in the input signal causes no further increase in the output signal.
Cutoff - Region of transistor operation where the input signal is reduced to a point where minimum transistor biasing cannot be maintained => the transistor is no longer biased to conduct. (no current flows)
e.g.: BC237, BC 337, BC 547, BC 557, 2N2222 (NPN and PNP)
Drain Gate Source
Determining Saturation, Cutoff or Conduction Vce=? + 10V Rc 10K B C E Ic Ie Ib Vbe R1 100K Determine the operation Region of the circuit below: Simplified Model Assume Transistor Current Gain = ß = 100 and Vbe = 0.65V Ie = Ic + Ib Ic = ß x Ib = 100 Ib Calculating Ib: 10 V = Vbe V + Ib x 100 x 10 3 (10 – 0.65) V = Ib x 100 x 10 3 => Ib = .0935 mA Thus Ic = 100 x Ib = 9.35 mA 10 V = Vce + Ic x 10 x 10 3 => Vce = - 83.5 V < 0V !! In reality Vce does not go negative because when it is almost zero (saturation), the current gain ( ß) does not apply any more and Vce sets at 0 volts. Thus the transistor is SATURATED Vce=? + 10V Rc 10K B C E Ic Ie Ib Vbe R1 100K
Building Logic Gates with Transistors & Resistors
A transformer is a passive electronics component and consists of a pair of wire coils coupled together with an iron core. The input coil is called the primary coil and the output coil is called the secondary coil.
Flash memory is a form of EEPROM that allows multiple memory locations to be erased or written in one programming operation. Normal EEPROM only allows one location at a time to be erased or written, meaning that flash can operate at higher effective speeds when the systems using it read and write to different locations at the same time. All types of flash memory and EEPROM wear out after a certain number of erase operations.
Flash memory is made in two forms: NOR flash and NAND flash. The names refer to the type of logic gate used in each storage cell.
NOR flash was the first type to be developed, invented by Intel in 1988 . It has long erase and write times, but has a full address/data (memory) interface that allows random access to any location. This makes it suitable for storage of program code that needs to be infrequently updated, as in digital cameras and PDAs . Its endurance is 10,000 to 100,000 erase cycles. NOR-based flash is the basis of early flash-based removable media; Compact Flash and SmartMedia are both based on it.
NAND flash from Toshiba followed in 1989 . It has faster erase and write times, higher density, and lower cost per bit than NOR flash, and ten times the endurance. However its I/O interface allows only sequential access to data. This makes it suitable for mass-storage devices such as PC cards and various memory cards , and somewhat less useful for computer memory. NAND-based flash has led to several much smaller removable media formats, MMC , Secure Digital and Memory Stick .
Flash memory forms the core of the removable USB interface storage devices known as keydrives .
NOR Flash uses hot electron injection for writing and tunnel release for erasing. NAND Flash uses tunnel injection for writing and tunnel release for erasing. Flash memory is erased through a mechanism called Fowler-Nordheim tunneling - a quantum mechanical tunneling process.