Electronics glossary
63 terms, each two or three plain sentences, with links to where Mokxi uses them.
Breadboard
A board of holes on a 0.1 inch grid for building a circuit with no soldering. Holes in a column are joined into one strip, so pushing a part’s leg into a hole connects it to everything else in that column, and the power rails along the edges run the length of the board instead.
Power rail
The long strip along a breadboard’s top and bottom edge, usually marked with a red and a blue or black line. One rail is meant for the supply voltage and the other for ground, and every hole in a rail is one continuous strip rather than the short five-hole columns in the middle of the board.
Center channel
The gap down the middle of a breadboard, 0.3 inch wide, that a DIP chip straddles so its two rows of pins land in different, unconnected strips on either side. Nothing electrical crosses it; it exists so a chip’s two pin rows do not short to each other.
Net
Every hole, pin and jumper wire that is electrically the same point, joined together before a circuit runs. A breadboard column, the wire pushed into it, and the part leg beside it are one net, and everything on a net is at one voltage at any instant.
Floating input
A digital input with nothing actively driving it, high or low. It is not a zero; it holds whatever charge was last on it, which can read as either level, briefly and unpredictably. A pull-up or pull-down resistor exists specifically to prevent this.
Pull-up resistor
A resistor from a digital input to the supply voltage, so the input reads a clean high when nothing else is pulling on it. A switch to ground then reads as low the instant it closes, and many microcontroller pins have one built in and switchable in firmware.
Pull-down resistor
The mirror of a pull-up: a resistor from a digital input to ground, so the input reads low at rest and a switch to the supply reads high. Logic gate inputs on a breadboard are usually held this way rather than the other, since a switch to the supply is the easier wire to run.
Debounce
Ignoring a switch’s extra transitions for a short window after the first one, so a single press is not counted several times. It can be done in software with a timer, or in hardware with a capacitor that slows the voltage enough that the chatter never crosses a full logic level.
Contact bounce
The chatter of a mechanical switch’s metal contacts as they close, caused by the contact physically rebounding a few times before it settles, rather than landing once. A single press or release can produce several extra electrical transitions within a few milliseconds.
Shift register
A chain of memory stages that moves its contents one place along every time it is clocked, with a new bit entering one end. The 74HC595 pairs one with a latch, so a whole byte can be shifted in a bit at a time and then shown on eight outputs all at once.
Latch
A small memory that holds a value until it is told to take a new one, rather than following its input continuously. The 74HC595’s storage register is a latch: its outputs sit still while data shifts in, and only change on the edge that copies the new byte across.
Tri-state (three-state)
An output that can be driven high, driven low, or disconnected from the net entirely, the third state being high impedance rather than a voltage. The 74HC595’s output-enable pin puts all eight outputs into this third state without disturbing the byte held in the latch.
High impedance (high-Z)
A pin that is effectively disconnected: it neither sources nor sinks current, and it does not hold the net at any particular voltage. An unpowered logic chip’s outputs sit high-Z, which is why a circuit built from real 74HC chips does nothing at all if the supply pins are not wired.
Logic gate
A circuit that outputs one of two levels based on the levels of its inputs, following one fixed rule such as AND or OR. Mokxi has both the ideal kind, drawn as a symbol with no supply pins, and the real 74HC family, packaged as chips with their own power and a measurable delay.
AND gate
A gate whose output is high only when every input is high. Two switches wired in series, both needing to close before current flows, behave the same way.
OR gate
A gate whose output is high when any input is high. Two switches wired in parallel, either one able to complete the circuit, behave the same way.
NAND gate
An AND gate with its output inverted: high unless every input is high, in which case it drops low. The 74HC00 packages four of them, and a NAND alone is enough to build every other gate, which is why it is often the first one taught.
NOR gate
An OR gate with its output inverted: low unless every input is low. Like the NAND, one NOR gate is enough on its own to build any other logic function.
XOR gate
A gate whose output is high only when its two inputs differ. The 74HC86 packages four of them, and an XOR is the core of a binary adder, where it produces the sum bit before a carry is worked out.
XNOR gate
An XOR gate with its output inverted: high only when its two inputs match. It is the equality check inside a digital comparator.
NOT gate (inverter)
A gate with one input and one output that always disagrees with it: high in gives low out, and low in gives high out. The 74HC04 packages six of them in one chip.
Flip-flop
A one-bit memory that changes on a clock edge rather than continuously following its input, the building block every counter and shift register is made from. The 74HC74 packages two D-type flip-flops, each with its own preset and clear pins.
Propagation delay
The time between an input changing and the output actually moving in response. Every chip in Mokxi’s logic family carries a real one taken from its datasheet, typically a few to a few tens of nanoseconds, rather than switching in zero time.
Inertial delay
A propagation delay that also swallows a pulse shorter than itself: a second input change before the first one has finished propagating cancels it, so a runt pulse never reaches the output at all. This is closer to what a real gate’s finite switching speed does than a plain fixed delay.
Truth table
A table listing a logic circuit’s output for every combination of its inputs. For two inputs there are four rows; the running circuit on the logic gates page is that table, built so you can press each row instead of read it.
Astable
A circuit with no stable resting state, so it oscillates on its own once powered. A 555 wired as an astable is the standard way to blink an LED or drive a tone with no microcontroller at all.
Monostable
A circuit with one stable resting state that, when triggered, produces exactly one timed pulse and then returns to rest on its own. A 555 wired this way is the common building block for a fixed-length delay or a debounced single pulse from a switch.
RC time constant
The time, in seconds, it takes a resistor-capacitor pair to close about 63 percent of the gap to whatever voltage it is charging or discharging toward, equal to the resistance in ohms times the capacitance in farads. A 555 astable’s frequency is set entirely by the RC time constants of its two timing resistors and its capacitor.
Duty cycle
The fraction of one cycle a signal spends high, usually given as a percentage. A PWM signal at 25 percent duty cycle is high for a quarter of every period and low for the rest, and a downstream LED reads that as roughly a quarter of full brightness.
PWM (pulse-width modulation)
Switching a digital pin on and off fast enough, at a chosen duty cycle, that anything downstream sees only the average and behaves as if it were being driven by an in-between voltage. It is how a digital output pin fades an LED or drives a hobby servo.
Ohm’s law
The current through a resistor equals the voltage across it divided by its resistance: I = V / R. It is the single equation behind sizing a current-limiting resistor for an LED and behind every pull-up and pull-down resistor on this site.
Forward voltage
The roughly fixed voltage an LED or any diode drops once it is conducting, commonly close to 2 volts for a red or green LED. Below it the diode barely conducts; above it, it takes whatever current the rest of the circuit allows, which is why it needs a resistor rather than a bare wire to the supply.
Current-limiting resistor
The resistor placed in series with an LED specifically to set how much current flows, since the LED itself will not limit it. Its value comes from Ohm’s law once the LED’s forward voltage is subtracted from the supply.
Thevenin equivalent
Any network of sources and resistors, seen from two terminals, can be replaced by one voltage source behind one resistance with no change to what those two terminals see. Mokxi’s resistor and LED parts each drive their pins this way, which is what lets a resistor act as a pull-up, a divider and an LED’s series limiter with no special cases in the code.
Voltage divider
Two resistors in series across a supply, with the output taken from the joint between them: Vout = Vin x R2 / (R1 + R2). It is the right way to scale a voltage down for an input that draws almost nothing, and the wrong way to power anything, because its output falls as soon as a load draws current.
Flyback diode
A diode fitted across a relay coil, solenoid or motor, band to the positive end, so that when the transistor switching it turns off, the coil’s current has a loop to die away in instead of driving the switch to a destructive voltage spike.
Saturation (transistor)
The fully-on state of a bipolar transistor used as a switch: the base has more current than the load needs, and the collector sits a tenth of a volt or less above the emitter, so the transistor wastes almost nothing. Too little base current and it is not saturated, drops volts across itself and runs hot.
Hysteresis
Two switching thresholds instead of one: a higher one to turn on and a lower one to turn off, so a signal hovering near the threshold cannot make the output chatter. A comparator gets it from a resistor feeding a little of its output back to its non-inverting input, and a sketch gets it from two numbers.
GPIO
A general-purpose input/output pin: one that firmware can configure, at run time, to read a digital level or drive one out. Almost every pin on the boards Mokxi models is a GPIO pin, with a handful given over permanently to things like the USB connection.
UART
A serial port that sends and receives one byte at a time, agreed on a baud rate rather than a shared clock line. It is what every board’s serial monitor talks over, whether it is called Serial in a sketch or USART0 in the datasheet.
Baud rate
How fast a UART sends bits, in bits per second. Both ends of a serial link have to agree on it beforehand, since nothing on the wire carries a clock to say otherwise; 9600 and 115200 are the two values almost everything defaults to.
I2C
A two-wire bus, data (SDA) and clock (SCL), that lets one controller talk to many chips. Each chip has a seven-bit address, and the one being called answers by pulling SDA low on the ninth clock of the address byte. Both lines need pull-up resistors.
SPI
A bus with a clock, a data line in each direction and a chip select wire per device. There are no addresses: the controller picks a device by pulling its chip select low, then clocks data in and out at the same time. It is faster than I2C and uses more pins.
Open drain
An output that can pull a line low or let go of it, but never drive it high; a pull-up resistor does that. Because nobody drives high, several devices can share one line without fighting, which is how I2C works.
State machine
A program organized as a set of named states, one variable saying which one it is in, and rules for what moves it from one to the next. It lets a sketch follow a sequence without delay() and without losing track of inputs.
Interrupt
A signal that pauses whatever the CPU is doing to run a short handler immediately, rather than waiting for the main loop to notice. It is how a board reacts to a button press or a finished UART byte within microseconds instead of on the next pass through loop().
Timer
A hardware counter, separate from the CPU, that counts clock ticks and can trigger an interrupt, generate a PWM waveform, or both, without the CPU’s attention in between. delay() and analogWrite() on every board Mokxi models are built on one.
Prescaler
A divider placed in front of a timer so it counts once every few clock ticks instead of every single one, trading resolution for a longer reach. The Arduino Uno’s hardware PWM on pin 9 uses a prescaler of 64 to bring 16 MHz down to a usable frequency.
ADC (analog-to-digital converter)
A peripheral that turns a voltage on a pin into a number the CPU can read, in steps rather than continuously. The Arduino Uno’s ADC gives a 10-bit result, 0 to 1023, across whatever reference voltage it is set to.
Memory map
The fixed table of addresses a chip’s datasheet assigns to its RAM, its flash and every peripheral’s registers. Mokxi’s boards use the real memory map for supported peripherals. Firmware built here still needs testing on the physical board.
RISC-V
An open instruction set architecture with no license fee attached. The ESP32-C3 implements one variant of it, RV32IMC, which is the core Mokxi’s own RISC-V engine runs.
ARM Cortex-M
A family of small ARM processor cores built for embedded use. The Raspberry Pi Pico’s RP2040 uses the Cortex-M0+, and the STM32F411 uses the Cortex-M4, both of which Mokxi runs on its own core.
AVR
The 8-bit microcontroller architecture Atmel built and Microchip now makes, used in the ATmega328P at the heart of the Arduino Uno. Mokxi’s own AVR core implements every ATmega328P instruction with the datasheet’s cycle counts.
Firmware
The compiled program that runs directly on a microcontroller, with no operating system underneath it in most of the boards Mokxi models. A sketch, once built, is firmware; the two words describe the same file at different stages.
ELF
The standard binary file format most compilers produce, carrying the program’s machine code, its starting address, and a symbol table. Mokxi’s boards load and run an ELF file rather than a raw binary, which is what lets the simulator know where each function actually is.
Sketch
Arduino’s name for a source file, still C++ underneath. The word survives because so much of the ecosystem’s documentation and habits are built around it, and Mokxi keeps using it for the same reason.
Emulator vs simulator
An emulator reproduces a real chip’s behavior closely enough that software cannot tell the difference, usually by running the same instructions the real chip would. A simulator is the broader word, covering anything that models a system’s behavior, including the analog side: the LEDs, the breadboard and the 555 timer that no chip is emulating anything for. Mokxi is both at once: an emulator for its CPU cores, and a simulator for the whole circuit around them.
SPICE in Mokxi
SPICE is the family of tools that solve a whole circuit as one set of equations, with device physics behind every part. Mokxi does it in two places. On the canvas it solves the analog corners of a circuit by nodal analysis over the nets a capacitor, inductor, op-amp, diode or transistor touches, and leaves the rest on its event-driven digital path, which is what keeps hundreds of parts running at real time: a diode is the Shockley equation, a transistor is Ebers-Moll and a MOSFET is level 1, each with its junction capacitance, all solved by Newton-Raphson, with an operating point, a DC and parameter sweep and a small-signal AC analysis. Run a SPICE deck, in the editor menu, runs a netlist on a SPICE engine: .op, .tran, .ac, .dc, .tf, .noise and .meas, subcircuits and parameters, Gummel-Poon BJTs, MOSFET levels 1 to 3, JFETs, behavioral sources and .temp, checked against ngspice on 42 benchmark circuits. It does not run BSIM MOSFET models, lossy transmission lines, XSPICE devices, or the .four, .sens, .pz and .disto analyses.
DIP (dual in-line package)
A chip package with two parallel rows of pins, spaced 0.1 inch apart within a row and 0.3 inch between the rows, built to straddle a breadboard’s center channel. Every 74HC chip and the NE555 that Mokxi models ships in one.
Register
A memory-mapped location a peripheral reads its configuration from and reports its status through, addressed like ordinary memory but wired to hardware instead of RAM. Setting a GPIO pin to an output, or reading whether a timer has fired, both happen by writing and reading registers.
Tactile switch (pushbutton)
A small momentary switch with a springy metal dome that clicks under a finger and releases on its own. Mokxi’s models one with real contact bounce, since that is the detail every debouncing tutorial depends on.
Slide switch
A switch with a knob that stays wherever it is left, rather than springing back like a tactile switch. Mokxi’s is a single-pole double-throw part: one common pin and two positions to move it between.
Seven-segment display
A digit made of seven LED segments, each driven independently, plus usually a decimal point. Driving all eight lines from a microcontroller with few pins to spare is the usual reason to reach for a 74HC595.
See the idea running
Every term above points at a part, a board or a lesson where you can watch it work rather than read about it.