Bench instruments reference

Every instrument you can add from the bench shelf, its front-panel controls, and how it maps into the SPICE simulation. For the how-to of adding and wiring instruments, see use the bench & draw leads.

All instruments start unwired: their net terminals are unconnected and they don't appear in the simulation until you draw a lead to a net (or, for the current probe, clamp a component). Editing any parameter while the board is energized triggers a live re-solve.

DC Supply: PSU (shown as "Power supply (PSU)")

A constant-voltage source with a series resistance.

Control	Range / default	Notes
Volts (knob)	0 to 30 V, step 0.1	Same value as the Voltage field
Voltage (field)	0 to 30 V	Type an exact value
Source R (series resistance)	≥ 0.001 Ω, default 0.1 Ω	The supply's internal resistance; raise it to model a weak/limited source

• Jack: red +. Return is through your designated ground.
• SPICE: a voltage source and a series resistor spliced between a synthetic internal node and your net, so the net keeps its name for the voltage overlay.
• Live edit: changing the voltage is an in-place alter (no reload).

Function Generator: FUNC GEN

A periodic source with a 50 Ω default output resistance.

Control	Range / default	Notes
Wave	sine / square / pulse / triangle
Freq (knob)	1 Hz to 1 MHz, logarithmic	Log scale gives fine low-frequency control
Amp (knob)	0 to 20 V	Amplitude
Offset (knob)	±20 V	DC offset
Duty (knob)	1 to 99 %	Square/pulse only

• Jack: yellow out.
• SPICE: SIN(...) for sine, PULSE(...) for square/pulse. Triangle is also a PULSE(...) source, with rise and fall each half a period and a negligible top width, so it is an exact linear ramp (within a few nanovolts of ideal) rather than a sine approximation.
• Live edit: frequency, amplitude, and offset changes alter in place for the same wave type. Changing the wave type reloads the circuit.

Logic Input: LOGIC

A digital high/low driver, for poking logic inputs and MCU-stub pins.

Control	Range / default	Notes
LO / HI toggle		Drives 0 or the high level
High level (V High)	0 to 30 V, default 3.3 V	Set it to match your logic rail

• Jack: purple out.
• SPICE: a DC source (level = V High when HI, else 0) with a 50 Ω series resistor.
• Live edit: toggling the level is an in-place alter.

Potentiometer: POT

A variable resistor, in two modes.

Control	Range / default	Notes
Variable resistor / Voltage divider	variable resistor (rheostat) default	Mode toggle
Wiper (knob)	0 to 100 %	Wiper position
Total resistance (Total R)	≥ 1 Ω, default 10 kΩ	End-to-end resistance

• Rheostat (2 terminals, A + W): a single variable resistor between A and W, value = Total R × wiper%. This is the classic dimmer wiring.
• Divider (3 terminals, A + W + Lo): a true voltage divider. An upper resistor A→W of Total R × (1 − wiper%) and a lower resistor W→Lo of Total R × wiper%, with W as the tap.
• Each leg is clamped to a minimum of 1 Ω so a fully-turned pot never shorts a node (which would wreck convergence).
• Live edit: turning the wiper is an in-place alter. Switching mode or changing Total R reloads. Switching modes keeps the A and W wires and only adds/drops the Lo terminal.

Voltage Probe: V PROBE

Reads a net's voltage and feeds the scope.

• Jack: tip, in the probe's trace color, clips to a net.
• Front panel shows a color swatch (its scope trace color) and the net's last operating-point voltage.
• SPICE: no element. The node voltage is read from the saved results.
• Fastest way to attach one: select a net and click ⌖ Probe this net in the bench header.

Current Probe: I PROBE

Clamps onto a component to read its current.

• Jack: clamp, dropped on a component (not a net).
• SPICE: for a primitive part, the device current is read natively; for a subcircuit part, a 0 V ammeter is spliced at the designated pad.
• Live edit: adding or removing a current probe always reloads (it changes the netlist).

Ground: GND

Not in the palette: it mirrors the ground net you designate in the Ground & Power panel and appears on the shelf automatically.

• Jack: black GND. (You re-designate ground in Ground & Power, not by dragging this off the board.)
• SPICE: the global reference, node 0. No element is emitted.

Live edit: alter vs. reload

circsim always picks the cheaper correct update:

• alter (instant, in place): changing a value, such as supply voltage, logic level, function-gen amplitude/frequency/offset (same wave), or pot wiper.
• Reload (rebuild the netlist): changing topology, such as moving a lead to a different net, changing a function-gen wave type, changing pot mode or Total R, or adding/removing a current probe.

You don't choose: circsim detects which happened and does the right thing. See architecture for the mechanism.