Electronics Essentials for 2.017Reviewing BasicsThe Op-AmpSlide Number 4Serial CommunicationsSlide Number 6Slide Number 7Pulse Width ModulationSome PWM UsesField Effect Transistor (FET)Bipolar Control with a MOSFET H-BridgeThe Basic DC Brush MotorProperties of the DC Brush MotorIncremental Encoders for ControlStepper MotorsMassachusetts Institute of Technology, Subject 2.017Electronics Essentials for 2.017Massachusetts Institute of Technology, Subject 2.017Reviewing Basics• Kirchoff’s Voltage rule: voltages V at a node are the same.• Kirchoff’s Current rule: sum of currents i flowing into and out of a node is zero.• Analogy: Voltage is like fluid pressure, current is like fluid volumetric flow rate. The wire is like a pipe.• Resistor R: V = IR, – Dissipation: Resistive Power P = I2R = V2/R– Analogy: viscous losses in pipe flow• Capacitor C: i = C dV/dt– Analogy: a hydraulic accumulator• Inductor H: V = L di/dt– Analogy: inertia of water in a pipeOhms, farads, fhenries, hMassachusetts Institute of Technology, Subject 2.017The Op-AmpTwo inputs (called inverting and non-inverting); one output.The output voltage is a HUGE gain multiplied by the difference between the inputs.Horiwitz’s & Hill’s golden rules: a. The op-amp enforces (in proper use) Vinv = Vnon-invb. No current flows into the device at either inputVinvVnon-invV+ (supply)V- (supply)VoutMassachusetts Institute of Technology, Subject 2.017VinvVnon-invV+V-VoutR1R2V(V-Vinv )/R1 = (Vinv -Vout )/R2 andVinv = Vnon-inv VR2 = Vinv (R1 +R2 ) – Vout R1 Vout = Vnon-inv (R1 + R2 )/R1 –VR2 /R1Letting R1 = R2, thenVout = 2Vnon-inv –VThe circuit inverts the input V and adds on 2Vnon-invIF Vnon_inv is ground, then Vout is just –V. This is just an inverting amplifier.Example Op-Amp: Adding a Voltage BiasVoltage bias useful for bringing signal levels into the range of sensors.The op-amp is discussed in detail by Horowitz and Hill, covering integrators, filters, etc.Massachusetts Institute of Technology, Subject 2.017Serial Communications• How to transmit digital information fast and reliably over a few wires?• Examples: RS-232, RS-485, etc. refer to pins & wires• A minimal case of RS-232 (DB25 connector is full case):– Asynchronous operation; both sides agree on BAUD rate– Three wires: send (TX), receive (RX), ground– No error checking! No flow control!Start bitnormally high0001 1 111Stop bit1’s(LSB)2’s 4’s 8’s 16’s32’s64’s 128’s(MSB)EXAMPLE using CMOS components:Successive bits read at midpoints, based on baud rate and on start bit leading edge5VGND2+4+8+16+128 = 158 = ‘_’ (underline)Massachusetts Institute of Technology, Subject 2.017• Garmin GPS25 series – Smart embedded device!• Similar to TT8’s interface with you – I/O strings are passed through a serial port• Reconfigurable through special commands• Output at 1Hz• String maintains exactly the same syntax: e.g., $GPRMC,hhmmss,V,ddmm.mmmm,N,dddmm.mmmm,E,000.0,000.0,ddmmyy,000.0,E,N,*XX<CR><LF>73 chars appear as one line:$GPRMC,hhmmss,V,ddmm.mmmm,N,dddmm.mmmm,E,000.0,000.0,ddmmyy,000.0,E,N,*XXEXAMPLE: A GPS StringMassachusetts Institute of Technology, Subject 2.017Serial devices communicate using characters encoded into bits. This includes upper- and lowercase letters, carriage returns and linefeeds, punctuation, etc.Characters are not numbers! E.g., char c = ‘7’ ;char d[2] = ‘92’ ;int n ;The numerical value of c is [00110111] (binary) or 55 (decimal).But because the ASCII characters ‘0’,’1’,’2’,’3’,’4’,’5’,’6’,’7’,’8’, and ’9’ occur in order, making simple conversions is easy:n = c – ‘0’ ;assigns to n the actual number 7. The ASCII character that goes with 7 is known as BEL – on many machines this will ring a bell if it is sent to the screen as a character! – printf(“%c”,n) ;How to turn d[2] into a number? n = 10*( d[0] - ’0’ ) + ( d[1] - ’0’ ) ; ASCII: American Standard Code for Information InterchangeMassachusetts Institute of Technology, Subject 2.017Pulse Width Modulation• A Regular WaveformPWM periodPulsewidth• PWM frequency (Hz) = 1 / PWM period• Duty cycle = Pulsewidth / PWM period• PWM frequencies typically range from 100Hz into MHz• Duty cycles can be used from 0 – 100%, although some systems use much smaller ranges, e.g. 5-10% for hobby remote servos.• The waveform has two pieces of information: Period and Pulsewidth, although they are usually not changed simultaneously.Volts VpeakMassachusetts Institute of Technology, Subject 2.017Some PWM Uses• The Allure: very fast, cheap switches and clocks to approximate continuous processes. Also, two-state signal resists noise corruption.• Sensors: PWM period is naturally related to rotation or update rate: Hall effect, anemometers, incremental encoders, tachometers, etc. • Communication: PWM duty cycle is continuously variable  like an D/A and an A/D.• Actuation: At very high frequencies, physical systems filter out all but the mean; i.e., Veffective = duty_cycle * VpeakHigh frequency switching is the dominant mode for powering large motors!Massachusetts Institute of Technology, Subject 2.017Field Effect Transistor (FET)• Like a “valve”, that is very easy to open or close. When FET is open, resistance is low (milli-Ohms); when FET is closed, resistance is high (mega-Ohms or higher)• Typically three connections:– Gate: the signal; low current– Source: power in– Drain: power out• N- and P-type junctions are common, and involve the polarity of the device. (N is shown)• Extremely sensitive to static discharge! Handle with care.• MOSFET: modern FET’s capable of handling higher power levels.gateLoadSupply_++_drainsourceMassachusetts Institute of Technology, Subject 2.017Bipolar Control with a MOSFET H-BridgegateLoadSupply_++_drainsourcegateLoadSupply+__+drainsourceN-channelP-channelMOSFET turns on when Vgate > VsourceMOSFET turns on when Vgate < VsourceloadP1P2N2N1ddddsssVssggggABCDTo make flow UL to LR, set A = GND and D = VsTo make flow UR to LL,Set B = GND and C = VsConnect A and B to Vs with pull-up resistors;Connect C and D to GND with pull-down resistors;Control all four gates explicitlyMassachusetts Institute of Technology, Subject 2.017The Basic DC Brush MotorS NiTorque   (coils)(flux density)(current i), or, in a given