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In "Place" on the toolbar, pick a part from the palette on the left and tap the canvas to place it (it snaps to a 20-unit grid). Switch to "Wire" and tap a part's terminal (the round dot), then another part's terminal, to draw a wire. Drag a part to move it, long-press to rotate it 90°, and double-tap to change its values. In "Delete", tap a part or a wire to remove it.

In "Run" mode, tap a switch to turn it ON / OFF; the current starts (or stops) at once. Press the play button (▶) to move the particles of current, and change their speed with the speed slider.

Double-tap a part to open its settings. Move a slider and the circuit is solved again on the spot, updating the current, voltage and power. You can change a battery's voltage and internal resistance, a resistor's resistance, a bulb's resistance and rated power, an LED's forward voltage and colour, an AC source's RMS voltage, frequency and phase, a capacitor's capacitance and an inductor's inductance.

The panel at the bottom of the screen gives the reason. A short circuit means the + and − of a source are connected with no resistance (check that wires or closed switches alone do not form a loop). A voltage conflict means sources with different voltages are in parallel with no resistance. An unsolvable circuit is a connection that cannot be calculated (such as a loop of ammeters only). The message names the part with the error, so look around that part.

An LED has a direction. Connect the flat side of the triangle (the anode) toward the + of the source and the tip (the cathode) toward the −. Reversed, no current flows. It also stays dark when the source voltage is below its forward voltage (2 V by default). If the current exceeds 50 mA, it "burns out" and goes dark. Do not connect it straight across a battery; add a resistor in series to stay safe (see the sample circuit "LED and resistor").

No. DENDOU solves any closed circuit with a source without a GND. If you place a GND, that point becomes the 0 V reference and the potential of each point is shown.

The 3 AC parts and the AC sample circuits (RL series, series resonance) are Pro features. Tap a locked part in the palette to open the Pro screen.

In AC, values are shown as RMS. The panel shows the RMS voltage and current, the phase difference, active power (W), reactive power (var), apparent power (VA) and the power factor. Select a part to draw its voltage and current waveforms (two periods); the particles of current move back and forth with the instantaneous value. Playback runs at 1/100 of real time, so one period of 50 Hz takes about 2 seconds.

Choose "Save" from "⋯" at the right end of the row with the play button, then pick a slot and a name (optional). "Load" in the same menu brings it back. Free has 1 slot, Pro has 5. Data is stored only on your device, and the circuit you are working on is saved automatically when you close the App.

"Undo" (↶) next to the play button undoes placing, wiring, moving, rotating, deleting, changing settings, resetting and loading, up to 20 steps. If you lose the circuit after zooming or panning, "Fit circuit" at the bottom right of the canvas fits the whole circuit on the screen.

Free: 9 DC parts, up to 8 parts, 1 save slot, ads. Pro (one-time purchase; see the store for the price): the 3 AC parts and the AC sample circuits, unlimited parts, 5 save slots, no ads.

Tap "Go Pro" on the toolbar and choose "Restore purchase". The App also checks your purchase automatically at launch (through the App Store on iOS and Google Play on Android). If it is not restored, check that you are signed in with the same App Store / Google Play account you bought with.

The Free version shows a Google AdMob banner. Buying the Pro version (a one-time purchase) removes it. On first launch the App asks whether to allow personalized ads, and no ad is loaded until you answer. Choosing "Don't allow" still shows ads; they are just not personalized.

Tap the "?" button at the top right of the toolbar, choose "Ad settings", then choose "Allow" or "Don't allow". The change applies immediately. With "Don't allow", ads are still shown but are not personalized. On iOS, the first launch asks through the system tracking (ATT) prompt instead of a screen of the App's own, and your answer sets the initial choice; this item is available once you have answered the prompt. The Pro version shows no ads, so this item is not shown there. See the privacy policy for details.

Tap the "?" button at the top right of the toolbar and choose "Show tutorial". "How to use" explains the controls and parts, and "Load a sample circuit" has 7 circuits (it replaces the current circuit).

When the first tutorial ends, the "Bulb and switch" circuit (two dry cells, a switch and a bulb) is placed automatically so you can try it at once. Tap the switch to light the bulb. If you do not need it, remove it with "Reset".

DENDOU's analysis engine solves circuits with modified nodal analysis (MNA) and is checked by automated tests based on published problems from school science, high-school physics and Japan's electrician and electrical-engineering (theory) exams. It uses idealized models (wires are 0 Ω, a battery is a voltage source plus internal resistance, an LED switches ON / OFF at its forward voltage), so it does not include the variation of real parts or the effects of temperature.

No. Circuits and settings are stored only on your device and are never sent to external servers. DENDOU has no server of its own and no account.