Building circuits

You build a circuit in CRUMB the way you would on your desk: connect parts to each other and to a power source. Push them into a breadboard, wire them straight to each other, or mix the two. This page covers connections, wires and breadboards, then power and what happens when something goes wrong.

Connections

A part connects to a circuit through three kinds of connection:

Pins are male, like the header pins on the Arduino Nano. A pin plugs into a terminal.
Terminals are female, like the holes in a breadboard. A terminal takes a pin or the end of a wire. A breadboard hole holds one, and some other terminals can hold several.
Wires are leads that bend, and their ends plug into terminals. Many parts’ legs are wires: a resistor’s legs are a single wire with the body along it, and an LED’s legs and a 9 V battery’s leads are wires too.

Because they’re wires, a part’s legs and leads can be reshaped. Select the part and press Wiring mode on the ribbon, or right-click it and choose Enter Wiring Mode, then drag their points as you would a jumper wire’s.

When you drag a part over a breadboard, its holes appear. Hold Ctrl to snap the part into the terminals under it, and add Shift to turn it to line up with them.

To check what’s connected, right-click a part and turn on Display Connections, and Show Connection Names to label each connection.

Parts can also have anchors, which join parts mechanically rather than electrically: see Welding with anchors. The scope and multimeter’s probes clip onto any pin, terminal or wire end.

Wires

Two parts are nothing but wire, for joining things anywhere, with or without a breadboard. With them you can build a whole circuit from parts and wires alone.

Jumper wire

The Jumper Wire is a length of solid wire that you route wherever you like, adding corners as you go. It’s a perfect conductor and never burns out. Its ends go into terminals.

When you place one, CRUMB goes straight into wiring mode, as long as Always for new on the BUILD tab is ticked (it is unless you untick it):

Click a terminal to seat the first end. The other end follows the mouse.
Right-click to put a corner in the wire wherever you want one.
Click another terminal to finish.

Escape steps back: first the last corner, then the wire’s ends, then out of wiring mode. To change a wire later, select it and press Wiring mode on the ribbon, or right-click it and choose Enter Wiring Mode. Then drag its points; Alt-drag adds a new point, and right-click a point to delete it. Finish Wiring on the right-click menu, or Finish on the ribbon, leaves wiring mode.

In wiring mode, right-click a point on a wire and choose Mount to Part… to make it ride along with a moving part, such as a cable running down a robot arm. Unmount from Part frees it again.

Prototyping wire

The Prototyping Wire is a DuPont jumper: a flexible lead with a connector on each end, for quick point-to-point wiring. Place one and CRUMB goes straight to plugging it in: click where the first end goes, then where the second goes.

Each end takes the shape of what it plugs into: a male pin into a terminal, or a female socket over a pin. So a prototyping wire can join two parts’ pins directly, with no breadboard in between.

Each new prototyping wire takes the next colour of a ten-colour jumper ribbon.

Wire colours

Set a jumper or prototyping wire’s colour in the inspector. Colour-code your wires the way you would on a real bench: red for power and black for ground make a circuit much easier to follow, for you and for anyone you share it with.

Breadboards

CRUMB comes with breadboards in several sizes. As on a real breadboard, the holes are joined in strips: anything pushed into the same strip is connected. The gap down the middle separates the two halves, so a chip can straddle it.

Power and ground

A circuit needs a power source, such as the Battery PP3 9 V. Its negative lead is the circuit’s ground: the 0 V that every voltage is measured from, and what the scope’s probes measure against. There’s no separate ground part to place.

The 9 V battery drains as your circuit uses it, and goes back to its Charge setting after Reset State. A voltage regulator turns a battery into a steady supply for logic chips and microcontrollers.

If nothing in the circuit connects to a supply’s negative terminal, there’s no ground to measure from. CRUMB can then stop with Circuit cannot be solved, explaining that every part of the circuit is floating. Connect the circuit to the supply’s negative side.

Finding parts

The Component Toolbox is the part library.

Search finds parts by name. You can leave letters out (rsistor finds resistors), but they must be in the right order. If the Workshop has parts that match too, they appear underneath.
Parts are grouped by category: Power, Passive, Semiconductor, Integrated Circuits, Digital Logic, Microcontrollers, Input Output, Sensors, Measurement, Prototyping, Protection and Miscellaneous.
Filter shows parts by where they came from: built in, your own, or from the Workshop. Sort orders them by category, name, rating or how recently they were edited or published.
Right-click a part and choose Add to Favourites to pin it at the top.
View Information on the right-click menu describes the part.
The options menu switches between a grid of cards and a list.

Setting a part’s values

Select a part to see its settings in the Inspector. The electrical settings, such as a resistor’s Resistance and Power Rating, are under Circuit Variables, and the rest under Component Variables. Hover over a setting to see what it does.

Number fields understand engineering notation: type 4.7k or 4k7 for 4,700, and the unit is shown beside the field.

When a part fails

Parts can be destroyed, just like real ones. Run a resistor over its power rating, an LED without a current-limiting resistor or a chip at the wrong voltage, and it fails. A failed part gets a red outline and stops conducting, and a panel in the corner of the 3D view lists what failed and why. Click a row to select the part. A part can also smoke, spark or pop as it fails, if its maker gave it those effects.

Reset failures in that panel, or Reset Failures on the ribbon, replaces just the failed parts with new ones, and carries on a run that Pause on Fail stopped.
Reset State puts the whole bench back as saved.

Fix the cause first, or the new part will fail too.

Failures ▼ on the ribbon sets how failures are checked. Check Every Tick, on by default, is what lets parts fail at all: turn it off and nothing fails and short circuits aren’t caught. Pause on Fail pauses the simulation the moment something fails, so you can look at the circuit as it was.

Short circuits

A power source that delivers more than a set current for 50 ms of simulated time fails with short circuit, the way a real battery or supply would overheat or shut down. The limit is 1 A by default; change it with Threshold, under Short Circuit Above in Failures ▼, or set it to 0 to turn the check off. Some faults are caught as soon as the circuit is analysed:

A wire straight across a source fails that source with short circuit across the source.
Two identical ideal sources wired in parallel switch one off with redundant ideal source. The circuit is fine electrically, but with no resistance there’s no way to tell how the two would share the current.
Two ideal sources at different voltages wired directly across each other can’t both be right. Where CRUMB can tell which source is at fault, it fails it with short circuit across the source. Otherwise the circuit has no solution, and CRUMB stops with Circuit cannot be solved, saying two power sources may be fighting. No part has failed then, so Reset failures has nothing to clear: fix the wiring, then run again.

Real batteries, like the 9 V battery, have internal resistance, so they’re not ideal sources. Two of them in parallel do solve: current flows from the fuller one into the other, and if it’s over the short-circuit limit for long enough, one fails with short circuit.

Labels

To mark up a circuit, add a Printed Label or a Floating Label from the BUILD tab. See Labels.