Classes and Functions

Schematic

When creating a schematic you may specify the following arguments: filename, font_size, font_family (ex. ‘serif’ or ‘sans-serif’), line_width, and dot_radius. The dot radius is the radius of solder-dots and pins.

You can also specify background and outline, both of which are colors. The default background is ‘white’ and the default outline is ‘none’. If you set background to ‘none’ be aware that this makes the concealers transparent, meaning that you cannot wire under components, instead you must wire to the pins. It is common to start by setting outline to allow you to see the SVG drawing area, and then later remove it when your schematic is complete. Pad arguments are used to adjust the size of the SVG

The size of the SVG canvas is automatically sized to fit tightly around the specified schematic objects. You might find that the text associated with input and output pins has a tendency to extend beyond the canvas. This is because no attempt is made to estimate the width of text. Instead, you can increase the width of the pin’s tile using its w parameter. In addition, you can also add padding when creating the schematic. There are five padding arguments. The most commonly used is pad, which simply adds the same padding to all four edges. In addition, you can control the individual edges using left_pad, right_pad, top_pad, and bottom_pad. These simply add to pad to create the final padding for each edge.

Wire

Draws a wire between two or more points given in sequence. Each point should be specified as a XY pair. Example:

Wire([(x0,y0), (x1,y1), (x2,y2), (x3,y3)])

Specifying wires before the components places them on a lower level, allowing the component to obscure the wires when needed.

Wire supports the kind argument, which may be either plain, |-, -|, |-|, or -|-. With plain, any-angle line segments are added between each of the points. With |-, -|, |-|, and -|- the wires are constrained to follow a Manhattan geometry (between each point there may be one, two, or three line segments that are constrained to be either purely vertical or purely horizontal. With |- there are two segments, with the first being vertical. With -|, there are also two segments, but the first is horizontal. With |-|, and -|- there there are three segments with the middle segment being half way between the two points. With |-|, the segments are vertical, horizontal, and vertical. With -|-, the segments are horizontal, vertical, and horizontal.

For example, if two resistors that are offset both horizontally and vertically are connected by a wire, the results depend on kind as follows:

Wire supports the line_width and color arguments.

Wire also supports arbitrary svgwrite drawing parameters. This can be useful to draw the wire with dashed lines:

Wire([(x0,y0), (x1,y1)], stroke_dasharray="4 2")

Wire provides the b, m, and e attributes that contain the coordinates of the beginning, the midpoint and the ending of the wire.

Label

Place a label. Five kinds of label are available, plain, arrow, arrow|, slash, and dot.

Label(kind='plain', name='plain', loc='se')
Label(kind='arrow', name='arrow', loc='se')
Label(kind='arrow|', name='arrow|', loc='se')
Label(kind='slash', name='slash', loc='se')
Label(kind='dot', name='dot', loc='se')

Here the labels are drawn with wires to give better context. The horizontal location of the labels is indicated with the vertical blue line.

Labels take the following arguments: kind, orient, name, value, loc, w, h, color, nudge, C, N, NE, E, SE, S, SW, W, NW, off, xoff and yoff. Currently value is ignored.

The C, N, NE, E, SE, S, SW, W, NW attributes contain the locations of the principle coordinates. The t attribute contains the coordinates of the label.

The kind may be ‘plain’, ‘arrow’, ‘arrow|’, ‘slash’ or ‘dot’. If ‘plain’ is specified, no symbol is added, only the name is displayed. If ‘arrow’ is specified, an arrow is added and the centered on the specified location. If ‘arrow|’ is specified, the arrow terminates on the specified location. If ‘slash’ is specified, a small slash is added through the center. It is generally used with buses to indicate the bus width. Finally, ‘dot’ adds a solder dot.

By default the width and height of the label are 1, meaning that a unit sized tile (50×50) is used. This is significant if the label is at the edge of the schematic. If the labels extend beyond the tile, they may extend beyond the computed viewbox for the schematic. You can fix this by specifying a larger width.

It is important to remember that C represents the center of the tile used by the label. Since the label will be on one side, C will not coincide with the apparent visual center of the label.

Components

This section documents the available components. Components include an invisible tile in which the component should fit. The tile extent is used when determining the size of the overall schematic. Each component requires that you specify location by giving the location of its principle coordinates or a pin. You can specify an placement offset using xoff, yoff, or off. You can also generally specify the orientation, the name, the value, and a text offset using orient, name, value, and nudge.

The orient is specified as a string that generally consists of either ‘v’ or ‘h’, indicating that a vertical or horizontal orientation is desired, but may include ‘|’ and ‘-’, indicating that the component should be flipped about either the vertical or horizontal axis.

The name and value are strings that are added to the component as labels, though not all components display the value. The nudge is a number that adjusts the placement of labels to avoid wires.

In addition, some components support other arguments, such as kind or loc.

You may pass wires directly under most components. The component will conceal the wire in those places where it should not be shown. This makes it simpler to wire up a schematic as you don’t need separate wires between a string of components that all fall in a line. Rather, you would just specify the wire first, and then it will run underneath the components. This trick works as long as you do not specify the schematic background as ‘none’.

Components generally place the location of their principle coordinates and the location of all their pins into named attributes.

Resistor

Draw a resistor.

Resistor(name='Rs', value='50Ω')

Resistors take the following arguments: orient, name, value, nudge, C, N, NE, E, SE, S, SW, W, NW, p, n, off, xoff and yoff.

The C, N, NE, E, SE, S, SW, W, NW attributes contain the locations of the principle coordinates. The p and n attributes contain the locations of the positive and negative terminals.

You may pass a wire directly under the resistor and the wire will be concealed by the resistor.

Capacitor

Draws a capacitor.

Capacitor(name='C1', value='1.2pF')

Capacitors take the following arguments: orient, name, value, nudge, C, N, NE, E, SE, S, SW, W, NW, p, n, off, xoff and yoff.

The C, N, NE, E, SE, S, SW, W, NW attributes contain the locations of the principle coordinates. The p and n attributes contain the locations of the positive and negative terminals.

You may pass a wire directly under the capacitor and the wire will be concealed by the capacitor. The capacitor is polarized with reference end being terminal n.

Inductor

Draws an inductor.

Inductor(name='L1', value='1μH')

Inductors take the following arguments: orient, name, value, nudge, C, N, NE, E, SE, S, SW, W, NW, p, n, off, xoff and yoff.

The C, N, NE, E, SE, S, SW, W, NW attributes contain the locations of the principle coordinates. The p and n attributes contain the locations of the positive and negative terminals.

You may pass a wire directly under the inductor and the wire will be concealed by the inductor.

Diode

Draws a diode.

Diode(name='D1')

Diodes take the following arguments: orient, name, value, nudge, C, N, NE, E, SE, S, SW, W, NW, p, n, off, xoff and yoff.

The C, N, NE, E, SE, S, SW, W, NW attributes contain the locations of the principle coordinates. The a and c attributes contain the coordinates of the anode and cathode terminals.

You may pass a wire directly under the diode and the wire will be concealed by the diode.

BJT

Draws a bipolar transistor. Two kinds of BJT are available, npn and pnp.

MOS(kind='n', name='Qn')
MOS(kind='p', name='Qp')

BJTs take the following arguments: kind, orient, name, value, nudge, C, N, NE, E, SE, S, SW, W, NW, p, n, off, xoff and yoff. kind may be npn or pnp, or simply n or p.

The C, N, NE, E, SE, S, SW, W, NW attributes contain the locations of the principle coordinates. The c, b and e attributes contain the coordinates of the collector, base and emitter terminals.

If kind is ‘p’ or ‘pnp’ a PNP symbol is drawn, otherwise an NPN symbol is drawn.

You may pass a wire directly under the transistor and the wire will be concealed by the transistor.

MOS

Draws a MOSFET. Three kinds of FET are available, nmos, pmos, and non-polarized.

MOS(kind='n', name='Mn')
MOS(kind='p', name='Mp')
MOS(kind='', name='M')

MOSFETs take the following arguments: kind, orient, name, value, nudge, C, N, NE, E, SE, S, SW, W, NW, p, n, off, xoff and yoff. kind may be nmos or pmos, or simply n or p. If an empty string is specified, the terminal locations are those of an nmos, but the arrow is not drawn.

The C, N, NE, E, SE, S, SW, W, NW attributes contain the locations of the principle coordinates. The d, g and s attributes contain the coordinates of the drain, gate and source terminals.

If kind is ‘n’ or ‘nmos’ an NMOS symbol is drawn; if kind is ‘p’ or ‘pmos’ a PMOS symbol is drawn; otherwise an unpolarized symbol is drawn.

You may pass a wire directly under the transistor and the wire will be concealed by the transistor.

Amplifiers and Converters

Draws an amplifier or a converter. Four kinds are available, single-ended (se), opamp (oa), differential amplifier (da) and comparator (comp).

Amp(kind='se', name='As')
Amp(kind='oa', name='Ao')
Amp(kind='da', name='Ad')
Amp(kind='comp', name='Ac')
Converter(kind='se', name='Cs')
Converter(kind='oa', name='Co')
Converter(kind='da', name='Cd')
Converter(kind='comp', name='Cc')

Amplifiers and Converters take the following arguments: kind, orient, name, value, C, N, NE, E, SE, S, SW, W, NW, p, n, off, xoff and yoff. kind may be se, oa, da or comp.

The C, N, NE, E, SE, S, SW, W, NW attributes contain the locations of the principle coordinates. The pi, i, ni po, o, and no attributes contain the coordinates of the positive input, the input, the negative input, the positive output, the output, and the negative output terminals. All 6 pin attributes are always available, even if they do not seem appropriate for the kind of amplifier drawn.

You can reshape the amplifier or converter using w and h to specify the width and height. The default values for each are 2, and you should not deviate too far from 2 or you will end up with an ugly symbol.

You may pass a wire or wires directly under the amplifier or converter and the wire will be concealed.

Gate

Draws a gate. Currently the only supported kind of gate is inv, an inverter.

Gate(kind='inv', name='U')

Gates take the following arguments: kind, orient, name, value, nudge, C, N, NE, E, SE, S, SW, W, NW, p, n, off, xoff and yoff. kind may be inv.

The C, N, NE, E, SE, S, SW, W, NW attributes contain the locations of the principle coordinates. The i and o attributes contain the coordinates of the input and the output.

You may pass a wire or wires directly under the gate and the wire will be concealed by the gate.

Source

Draws a source. Eight kinds of source are available, empty, vdc, idc, sine, sum (summer), mult (multiplier), cv (controlled voltage) and ci (controlled current).

Source(kind='empty', name='Ve')
Source(kind='vdc', name='Vd')
Source(kind='idc', name='Id')
Source(kind='sine', name='Vs')
Source(kind='sum', name='S')
Source(kind='mult', name='M')
Source(kind='cv', name='Vc')
Source(kind='ci', name='Ic')

Sources take the following arguments: kind, orient, name, value, nudge, C, N, NE, E, SE, S, SW, W, NW, p, n, off, xoff and yoff. kind may be empty, vdc, idc, sine, sum, mult, cv or ci.

The C, N, NE, E, SE, S, SW, W, NW attributes contain the locations of the principle coordinates, but unlike all other components, these are evenly distributed about the circle that envelopes the source. The p and n attributes contain the coordinates of the positive and negative pins. The pin attributes are always available, even if they do not seem appropriate for the kind of source drawn.

You may pass a wire or wires directly under the source and the wire will be concealed by the source.

Switch

Draws a switch. Two kinds of switch are available, spst (single-pole, single-throw) and spdt (single-pole, double-throw).

Switch(kind='spst', name='φ₁')
Switch(kind='spdt', name='φ₂')

Switches take the following arguments: kind, orient, name, value, dots, nudge, C, N, NE, E, SE, S, SW, W, NW, i, o, ot, ob, off, xoff and yoff. kind may be spst or spdt. The dots argument determines whether the poles of the switch should be denoted with large dots.

The C, N, NE, E, SE, S, SW, W, NW attributes contain the locations of the principle coordinates. The i ot, o and ob attributes contain the coordinates of the input, the top output, the output, and the bottom output pins. The pin attributes are always available, even if they do not seem appropriate for the kind of switch drawn.

You may pass a wire or wires directly under the switch and the wire will be concealed by the switch.

Box

Draws a box.

Box(name='4 bit', value='Flash')
Box(name='𝘻⁻¹', w=1, h=1)

Boxes take the following arguments: orient, name, value, nudge, line_width, background, w, h, C, N, NE, E, SE, S, SW, W, NW, i, pi, ni, o, po, no, off, xoff and yoff. In addition, you may specify SVGwrite arguments, as shown in the example below.

The C, N, NE, E, SE, S, SW, W, NW attributes contain the locations of the principle coordinates. They are arranged along the surface of the box.

The i pi, ni and o, po, no attributes contain the coordinates of the input and output pins.

Boxes also support arbitrary svgwrite drawing parameters. This can be useful to draw the box with dashed lines:

Box(w=1, h=1, stroke_dasharray="4 2")

Crossing

Draws a wire crossing in such a was as to maintain symmetry in schematics.

Crossing()
Crossing(w=2, h=2)

Crossings take the following arguments: , pass_under, w, h, C, N, NE, E, SE, S, SW, W, NW, pi, ni, po, no, off, xoff and yoff.

The C, N, NE, E, SE, S, SW, W, NW attributes contain the locations of the principle coordinates. The pi and pi attributes contain the coordinates of the input and output pins.

Ground

Draws a ground.

Ground()

Grounds take the following arguments: orient, name, value, nudge, C, N, NE, E, SE, S, SW, W, NW, t, off, xoff and yoff. Currently value is ignored.

The C, N, NE, E, SE, S, SW, W, NW attributes contain the locations of the principle coordinates. The t attribute contains the coordinates of the ground’s terminal.

Pin

Draws a pin. Four kinds of pin are available, none, dot, in, and out.

Pin(kind='none', name='none', value='none value')
Pin(kind='dot', name='dot', value='dot value')
Pin(kind='in', name='in')
Pin(kind='out', name='out')

Here the pins are drawn with wires to give better context. The horizontal location of the pins is indicated with the vertical blue line.

Pins take the following arguments: kind, orient, name, value, nudge, w, h, color, C, N, NE, E, SE, S, SW, W, NW, t, off, xoff and yoff. Currently value is ignored for in and out pins.

The C, N, NE, E, SE, S, SW, W, NW attributes contain the locations of the principle coordinates. The t attribute contains the coordinates of the pin.

It is important to remember that C represents the center of the tile used by the pin. Since the pin label will be on one side, C will not coincide with the apparent visual center of the pin and its label.

Pins of kind none do not draw a symbol. Rather they are used to place labels at a particular point. dot pins place a small filled circle that is usually used to represent a solder dot (though you can change the color to the background color, generally ‘white’, and place it between two crossing wires to create a visual gap in the lower wire). Pins of type in and out render with a hollow circle that is offset slightly a wire terminates on one side. These two pin types ignore the value argument.

By default the width and height of the pin are 1, meaning that a unit sized tile (50×50) is used. This is significant if the pin is at the edge of the schematic. If the labels extend beyond the tile, they may extend beyond the computed viewbox for the schematic. You can fix this by specifying a larger width.

Dot

Draw a solder dot (a small filled circle) or a wire gap (a small filled circle with the color of the background that is placed between two crossing wires). Dot is just an alias for Pin, except that the default kind is ‘dot’.

It is common to place a dot at a level between two crossing wires and specify a color of white to create a pass-under.

Dot()

Label

Place a label. Five kinds of label are available, plain, arrow, arrow|, slash, and dot.

Label(kind='plain', name='plain', loc='se')
Label(kind='arrow', name='arrow', loc='se')
Label(kind='arrow|', name='arrow|', loc='se')
Label(kind='slash', name='slash', loc='se')
Label(kind='dot', name='dot', loc='se')

Here the labels are drawn with wires to give better context. The horizontal location of the labels is indicated with the vertical blue line.

Labels take the following arguments: kind, orient, name, value, loc, w, h, color, nudge, C, N, NE, E, SE, S, SW, W, NW, off, xoff and yoff. Currently value is ignored.

The C, N, NE, E, SE, S, SW, W, NW attributes contain the locations of the principle coordinates. The t attribute contains the coordinates of the label.

The kind may be ‘plain’, ‘arrow’, ‘arrow|’, ‘slash’ or ‘dot’. If ‘plain’ is specified, no symbol is added, only the name is displayed. If ‘arrow’ is specified, an arrow is added and the centered on the specified location. If ‘arrow|’ is specified, the arrow terminates on the specified location. If ‘slash’ is specified, a small slash is added through the center. It is generally used with buses to indicate the bus width. Finally, ‘dot’ adds a solder dot.

By default the width and height of the label are 1, meaning that a unit sized tile (50×50) is used. This is significant if the label is at the edge of the schematic. If the labels extend beyond the tile, they may extend beyond the computed viewbox for the schematic. You can fix this by specifying a larger width.

It is important to remember that C represents the center of the tile used by the label. Since the label will be on one side, C will not coincide with the apparent visual center of the label.

Location Functions

shift

Shifts a point by specified amounts in both the x and y directions.

shift(point, dx, dy)

point is an (x, y) coordinate and dx and dy are numbers. The return value is (x + dx, y + dy).

shift_x

Shifts a point by specified amount in the x direction.

shift_x(point, dx)

point is an (x, y) coordinate and dx is a number. The return value is (x + dx, y).

shift_y

Shifts a point by specified amount in the y direction.

shift_y(point, dy)

point is an (x, y) coordinate and dy is a number. The return value is (x, y + dy).

with_x

Returns the first argument (a coordinate pair) with the x value replaced with the second argument. The second argument may either be a number or a coordinate pair.

with_x(point, x)

with_y

Returns the first argument (a coordinate pair) with the y value replaced with the second argument. The second argument may either be a number or a coordinate pair.

with_y(point, y)

with_min_x

Returns the first argument (a coordinate pair) with the x value replaced with the smallest of the remaining arguments. The remaining arguments may either be numbers or a coordinate pairs.

with_min_x(point, ...)

with_max_x

Returns the first argument (a coordinate pair) with the x value replaced with the largest of the remaining arguments. The remaining arguments may either be numbers or a coordinate pairs.

with_max_x(point, ...)

with_min_y

Returns the first argument (a coordinate pair) with the y value replaced with the smallest of the remaining arguments. The remaining arguments may either be numbers or a coordinate pairs.

with_min_y(point, ...)

with_max_y

Returns the first argument (a coordinate pair) with the y value replaced with the largest of the remaining arguments. The remaining arguments may either be numbers or a coordinate pairs.

with_max_y(point, ...)

midpoint

Returns the point midway between two points.

midpoint(point1, point2)

midpoint_x

Returns the point with x value midway between two points and the y value of the first point.

midpoint_x(point1, point2)

midpoint_y

Returns the point with y value midway between two points and the x value of the first point.

midpoint_y(point1, point2)

Exceptions

In the rare cases where SVG_Schematic it raises an error, it uses Inform Error. SVG_Schematic is a wrapper around svgwrite. It is not clear what exceptions it will raise, but at a minimum it would raise OSError if it is unable to open or close the SVG file. Thus you should catch these two exceptions. See Non Inverting Amplifier to see how this is done.