Getting Started
iCircuit allows you to work on one circuit at a time. You start the app in the Circuit Browser (featured to the right).
The browser uses folders just like your desktop computer. The main folder is called Home and all other folders are children on it.
Each circuit is represented as a gray thumbnail. Simply tap one of these thumbnails to open the circuit.
You can create new circuits by tapping the "New Circuit" icon. This will create a new circuit in the active folder and will open that circuit.
In addition to the Home folder, there are two other special folders:
Trash is used to store circuits that you want to delete. When you are prepared to empty the trash, select its icon and an "Empty Trash" button will appear in the upper right of the browser.
Inbox contains any circuits that you open from a web page or an email. This folder only appears when you have items in the Inbox.
The Circuit Editor
WIRING

Wires are drawn using a special wiring mode of the editor. To activate this mode, press the little pen tool in the toolbar. Now when you drag around on the screen, wires will be drawn.

It is recommended that you pin the circuit down while drawing wires as it will make the process much easier.

The Oscilloscope
There is only 1 oscilloscope per circuit. You can control what it is potting using the Multimeter tool. Variables on the Multimeter with circles by their names can be added to the scope - simply tap on the variable name and it will be added. Tap on the name to remove it again. Every time you add the signal to the scope, it will be assigned a color randomly.
The oscilloscope can display multiple signals either all on one graph or stacked on multiple graphs. You can select the mode by pinching or stretching your fingers vertically on the scope.
The amount of time shown on the scope can be controlled by pinching or stretching horizontally.
Elements
Elements comprise a circuit. Everything from a 7-segment display to a wire are elements.
A single element has one or more "posts" that you can connect wires or other elements to. Posts are represented as thick lines and are drawn using an empty circle when not connected. The analog SPDT switch (relay) to the left has 4 posts: 2 inputs (right), 1 output (left), and 1 control signal (top).
Elements also have "handles" that are used to move, reorient, or resize the element. An element will have either 1 or 2 handles and often the handles are in the same position as the posts of the element. Handles appear as white squares when an element is selected. On right is what the SPDT switch looks like when selected.
You drag handles to change the shape and orientation of elements.
WIRE

Wires join two posts together or connect to other wires. They do not have any resistance, capacitance, or inductance - they are ideal.
You can move or reshape wires like any other element because they have handles. Wires are created by entering a special wiring mode of the editor. Click the wire button (shown on the left) in the toolbar to enter this mode. While in this mode, you use your finger to draw wires anywhere on the circuit. These new wires will appear red while you are creating them and will return to the normal wire color when complete.
Wires are also sometimes automatically created when you drag an element and it needs to stay connected to other posts or wires.
VOLTAGE SOURCE

The Voltage Source comes in 6 varieties.
D/C This voltage source provides a constant voltage between its upper and lower terminals.
A/C Provides an oscillating sine wave at a specified frequency and with an optional DC offset.
v(t) = Max Voltage * sin(Frequency * 360 * t + PhaseOffset) + DC Offset
The Phase Offset is provided so that you can have two A/C sources that interfere with one another.
Square Waves are similar to A/C waves but generate square waves instead of sine waves. They also have a configurable Duty Cycle.
Triangle is like A/C but the generated voltages follow a triangular shape instead - a linear ramp up followed by a linear ramp back down.
Sawtooth is also like A/C but the generated voltages follow a sawtooth shape - they ramp up and then instantly drop.
Pulse waves are normally 0 V, but peak at the specified frequency. These are great for generating digital circuit clocks and for bothering capacitors.
CURRENT SOURCE

Current sources aren't often used in real-world circuits, but they are often used when learning circuits for the first time. They simply generate a constant current between the two posts.
Current sources introduce one bit complexity: the simulation algorithm cannot proceed until all current sources have been placed into a true circuit - a path from one of its posts to the other post through wires or other elements. Because of this, the circuit will always stop when you add a current source. To resume simulation, you will have to wire the current source and the turn the circuit back on.
This constraint is very similar to the requirement that voltage sources should not ever be shorted out by creating paths of 0 resistance.
GROUND

Ground elements connect elements to 0V.
They are very convenient to create shortcuts through your circuit. They have no properties.
You can regard a ground element as earth ground.



RESISTOR

Resistors are the elemental current carriers. The abide by Ohm's law:

v = i * R







CAPACITOR

Capacitors are the element charge holders. Their current is proportional to the change of voltage over their terminals:

i(t) = C * dv/dt

In DC circuits, they act like an open circuit. In AC circuits they act like short circuits that introduce a 90 deg phase. Coupled to a resistor, capacitors make for very easy filters.

INDUCTOR

Inductors are the inverse of capacitors and produce voltages based on changes in current:

v(t) = L * di/dt

In DC circuits, inductors act like wires.





SPEAKER

Speaker elements produce sound waves that are equivalent to the voltage applied across its terminals.

Speakers act as resistors - they do not introduce any capacitance or inductance. The volume of the produced audio is proportional to the maximum voltage ever witnessed by the speaker element.

iCircuit even produces this sound! You will notice however that there is a 1 sec delay between the voltage applied and the actual sound produced by the application. This 1 sec buffer is there in order to keep a constant sound even when the app is slowed down by other tasks.

BUZZER

Buzzers produce 2 kHz buzzing sound when a DC voltage is applied to its terminals. Buzzers have a resistance and only produce sound if the voltage drop is greater then 2 V.

They are great for testing digital circuits if you get bored with LEDs.





LEDS

LEDs are light-emitting diodes. They have a forward voltage drop, but that drop is usually larger than a normal diode's voltage drop. The brightness of the light emitted is proportional to the current through the LED.

You can change an LED's nominal color by setting its Red, Green, and Blue values. For each of these, 0 means no mixture of that color component, while 1 means a full mixture. For example, yellow can be set by setting Red = 1, Green = 1, and Blue = 0.

SPST SWITCH

Switches either connect and disconnect their two posts. You can toggle the switch's state by double-tapping them element.







SPDT SWITCH

SPDT switches join one of two posts into one. The toggle state of the switch controls which of those posts is connected. You can toggle the state by double-tapping on the element.







ANALOG SWITCH

The analog switch acts as a relay that either connects or disconnects its two posts based upon a control signal. When the control signal is greater than 2.5 V, the switch is closed; otherwise, it is open.

You can set the On (usually small) and Off resistances (usually large) to closer match physical relays.

These elements are great for joining digital circuits to analog.



SPDT ANALOG SWITCH

This element acts as a relay that joins two posts into one and is again controlled by a digital control signal. When the signal is greater than 2.5 V then one post is connected, when less the other post is connected.







DIODE

Diodes are the basic semiconductor element. When active, diodes introduce a voltage that is specified as the Forward Voltage. Diodes do not permit current in the direction opposite the arrow.





ZENER DIODE

Zener diodes are like diodes but allow for reverse currents. The Zener Voltage specifies the reverse breakdown voltage.







BJT TRANSISTOR (NPN OR PNP)

BJT Transistors are found in two doping varieties, NPN and PNP. They are often used as single stage amplifiers or combined with other transistors to form multistage amplifiers.









MOSFET (NPN OR PNP)

MOSFETs are the second type of transistor supported by the application. MOSFETs are often used as the building blocks of digital circuits.

The property Beta is used to represent both the semiconductor process constant k, and the geometry W/L. That is:

Beta = k * (W/L)



OP-AMP

The op-amp is a differential amplifier with a very large amplification of 100,000. You almost always add some kind of negative feedback to an op-amp in order to control this amplification.











ADC

The ADC is an analog-to-digital converter. You specify the precision of the conversion using the Bits property. The In pin is sampled and compared to the V+ pin. That ratio is then multiplied by 2^Bits to determine the output value. The digital pins expect TTL levels (0 to 5 V where 2.5 V is the trigger point).











DAC

The DAC is a digital-to-analog converter. You specify the precision of the conversion using the Bits property. The O pin is ranges from 0 V to V+ based on the inputs.











INVERTER

The inverter inverts TTL logic levels. That is, 5V on input will produce 0 V on the output post.

The inverter also has a slew rate that produces less chatter in analog circuits than most digital elements will produce.





AND, NAND, OR, NOR, AND XOR GATES

These logic gates are TTL level digital circuit elements. The number of inputs are controlled with the # of Inputs property.









JK AND D FLIP-FLOPS

The JK and D flip-flops are the basic bit storage units of digital circuits. They are clocked on the rising edge of the clock signal and require appropriate reset logic levels to be applied before they work.







DIGITAL COUNTER

The digital counter increments a binary representation of a number on every leading edge of the clock signal. The number of bits used to represent that number are controlled by the Bits property. On rollover, the number is reset to 0.











7-SEGMENT DISPLAY

The 7-segment display is a collection of 7 LEDs that can be used to display alpha-numeric characters. However, without an encoder, the 7-segment display isn't very useful. The next version of iCircuit will feature programmable chips that will make this element more useful.