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Description:

rkmcodes 0.6

Version: 0.6
Released: 2023-04-14

RKM codes are used to represent electrical quantities in labels, particularly on
schematics and on the components themselves. They are standardized in various
national and international standards, including: IEC 60062 (1952) (formerly IEC 62),
DIN 40825 (1973), BS 1852 (1974), IS 8186 (1976) and EN 60062 (1993).
IEC-60062 was significantly updated in 2016.
RKM codes were originally used as part marking codes. This shorthand
notation is widely used in electrical engineering to denote the values of
resistors and capacitors in circuit diagrams and in the production of electronic
circuits (for example in bills of material and in silk screens). This method
avoids overlooking the decimal separator, which may not be rendered reliably on
components or when duplicating documents.
The popularity of RKM codes was fading because they address a problem that is
less common today. However they are making something of a come back as all the
characters in a RKM code are either letters or digits and so they can be
embedded in a software identifier without introducing illegal characters.
IEC 60062 is described in https://en.wikipedia.org/wiki/RKM_code.
Essentially an RKM version of a number is the number with a scale factor where
the decimal point is replaced by the scale factor. For example, a resistance of
4.7kΩ becomes 4k7. If there is no scale factor, the decimal point is replaced by
a letter that signifies the type of the component. For example, a resistance of
4.7Ω becomes 4r7.
Resistance examples:
R47 → 0.47 Ω
4R7 → 4.7 Ω
470R → 470 Ω
4K7 → 4.7 kΩ
47K → 47 kΩ
47K3 → 47.3 kΩ
470K → 470 kΩ
4M7 → 4.7 MΩ
In the standard, large values are assumed to be resistances and small values are
assumed to be capacitances. So 4k7 is a resistance and 2n5 is a capacitance.
However, this package also supports a version of RKM codes where the units are
not implied by the value, making RKM codes suitable for a wider variety of value
types, such as voltage, current, and inductance.

Installing
This package converts RKM codes to QuantiPhy Quantities and Quantities to RKM codes.
Install with:
pip3 install --user rkm_codes
Requires Python 3.6 or better.

Converting to and from RKM Codes
The following is a simple example of how to convert back and forth between RKM
codes and Quantities:
>>> from rkm_codes import from_rkm, to_rkm
>>> r = from_rkm('6K8')
>>> r
Quantity('6.8k')

>>> to_rkm(r)
'6K8'
Notice that in this case the quantity does not include units. That is because by
default rkm_codes assumes unitless numbers. You can change this behavior. Out
of the box rkm_codes supports two kinds of numbers, unitless and those that
follow the IEC60062 standard. You can switch between those two kinds of numbers
using something like this:
>>> from rkm_codes import set_prefs, IEC60062_MAPS, UNITLESS_MAPS
>>> r = from_rkm('6k8')
>>> r
Quantity('6.8k')

>>> set_prefs(rkm_maps=IEC60062_MAPS)
>>> from_rkm('6k8')
Quantity('6.8 kΩ')

>>> set_prefs(rkm_maps=UNITLESS_MAPS)
>>> from_rkm('6k8')
Quantity('6.8k')
In either case, rkm_codes allows you to explicitly specify the units, which
always overrides any implied units:
>>> set_prefs(rkm_maps=UNITLESS_MAPS)
>>> from_rkm('6kΩ8')
Quantity('6.8 kΩ')

>>> i = from_rkm('2uA5')
>>> i
Quantity('2.5 uA')
The primary argument for to_rkm can be a string, a float, or a quantity:
>>> print(to_rkm('12.5 nA', prec=2))
12n5

>>> print(to_rkm(12.5e-9, prec=2))
12n5

>>> from quantiphy import Quantity
>>> print(to_rkm(Quantity('12.5 nA'), prec=2))
12n5
When converting to an RKM code, you can instruct that the units be included:
>>> to_rkm(i, show_units=True)
'2µA5'
You can also indicate how many digits should be included:
>>> to_rkm(i.add(1e-9), prec=5, show_units=True)
'2µA501'
Normally, any excess zeros are removed, but you can change that too:
>>> to_rkm(i.add(1e-9), prec=5, show_units=True, strip_zeros=False)
'2µA50100'
To shorten the output code it is possible to remove the base code when it is
extraneous:
>>> from quantiphy import Quantity
>>> to_rkm(Quantity('470Ω'), show_units=False)
'470'

>>> to_rkm(Quantity('470Ω'), show_units=False, strip_code=False)
'470r'
Here is a short program that illustrates some of the options of to_rkm:
>>> from rkm_codes import from_rkm, to_rkm, set_prefs, IEC60062_MAPS

>>> set_prefs(prec=4)

>>> q = from_rkm('0μΩ47')
>>> while q < 1e6:
... vals = [
... q,
... to_rkm(q),
... to_rkm(q, strip_code=False),
... to_rkm(q, show_units=True),
... to_rkm(q, strip_zeros=False)
... ]
... print(' '.join([' {:<9}'.format(v) for v in vals]).strip())
... q = q.scale(10)
470 nΩ 470n 470n 470nΩ 470n00
4.7 uΩ 4µ7 4µ7 4µΩ7 4µ7000
47 uΩ 47µ 47µ 47µΩ 47µ000
470 uΩ 470µ 470µ 470µΩ 470µ00
4.7 mΩ 4m7 4m7 4mΩ7 4m7000
47 mΩ 47m 47m 47mΩ 47m000
470 mΩ 470m 470m 470mΩ 470m00
4.7 Ω 4r7 4r7 4Ω7 4r7000
47 Ω 47 47r 47Ω 47r000
470 Ω 470 470r 470Ω 470r00
4.7 kΩ 4K7 4K7 4KΩ7 4K7000
47 kΩ 47K 47K 47KΩ 47K000
470 kΩ 470K 470K 470KΩ 470K00
If you prefer not to use the small SI scale factors, which would be more in
keeping with IEC60062 for resistors, you can specify that quantiphy.Quantity
use a restricted output_sf:
>>> q = from_rkm('0μΩ47')
>>> q.output_sf = 'TGMk' # this line is new
>>> while q < 1e6:
... vals = [
... q,
... to_rkm(q),
... to_rkm(q, strip_code=False),
... to_rkm(q, show_units=True),
... to_rkm(q, strip_zeros=False)
... ]
... print(' '.join([' {:<9}'.format(v) for v in vals]).strip())
... q = q.scale(10)
470e-9 Ω 0 0r 0Ω r0000
4.7e-6 Ω 0 0r 0Ω r0000
47e-6 Ω 0 0r 0Ω r0000
470e-6 Ω r0005 r0005 Ω0005 r0005
4.7e-3 Ω r0047 r0047 Ω0047 r0047
47e-3 Ω r047 r047 Ω047 r0470
470e-3 Ω r47 r47 Ω47 r4700
4.7 Ω 4r7 4r7 4Ω7 4r7000
47 Ω 47 47r 47Ω 47r000
470 Ω 470 470r 470Ω 470r00
4.7 kΩ 4K7 4K7 4KΩ7 4K7000
47 kΩ 47K 47K 47KΩ 47K000
470 kΩ 470K 470K 470KΩ 470K00
You can create your own maps by passing in a dictionary that maps a RKM base
code character into a scale factor and units. For example, you could create
a map that uses ‘d’ or ‘D’ to represent the decimal point in numbers without
scale factors rather than ‘r’, ‘c’, etc. For example:
>>> set_prefs(rkm_maps=dict(d=('', ''), D=('', '')))
>>> from_rkm('6d8')
Quantity('6.8')

>>> from_rkm('2d5')
Quantity('2.5')
Passing None for the value of a map returns it to its default value.
If rkm_codes encounters a RKM base code character that is not in the map, it
simply uses that character. In this way, scale factors are handled:
>>> from_rkm('6k8')
Quantity('6.8k')
When converting from Quantities to RKM codes, you can override the default
mappings from units to RKM base code characters. The default mapping maps ‘Ω’
and ‘Ohm’ to ‘r’, ‘F’ to ‘c’, ‘H’ to ‘l’, ‘V’ to ‘v’, and ‘A’ to ‘i’. However,
you may prefer uppercase base characters, which is more in alignment with the
original standard. To get that, you can use something like this:
>>> rkm_base_code_mappings = {
... 'Ω': 'R',
... 'Ohm': 'R',
... 'F': 'C',
... 'H': 'L',
... 'V': 'V',
... 'A': 'I',
... }
>>> set_prefs(rkm_maps=IEC60062_MAPS, units_to_rkm_base_code=rkm_base_code_mappings)
>>> r = from_rkm('k0012')
>>> to_rkm(r)
'1R2'
You can control the scale factors used by to_rkm() by setting map_sf using
set_prefs. The default maps ‘u’ to ‘μ’ and ‘k’ to ‘K’. You might wish to
prevent the use of ‘μ’ while retaining the use of ‘K’, which you can do with:
>>> set_prefs(map_sf=dict(u='µ'))
>>> c = from_rkm('5u')
>>> to_rkm(c)
'5µ'

Finding RKM Codes
find_rkm is available for finding the RKM codes embedded in text strings.
Using it, you can iterate through all the numbers specified using RKM:
>>> from rkm_codes import find_rkm

>>> text = '''
... An RKM code that may include explicitly specified. Examples of
... acceptable RKM codes for resistance include: R47 (0.47 Ω), 4R7
... (4.7 Ω), 470R (470 Ω), 4K7 (4.7 kΩ), 47K (47 kΩ), 47K3 (47.3 kΩ),
... 470K (470 kΩ), and 4M7 (4.7 MΩ).
... '''
>>> for num in find_rkm(text):
... print(num)
470 mΩ
4.7 Ω
470 Ω
4.7 kΩ
47 kΩ
47.3 kΩ
470 kΩ
4.7 MΩ
When the RKM code is not isolated by punctuation or spaces it can get confused
by leading and trailing text. You can often resolve this issue by restricting
the matches to either the leading or trailing digit forms of the RKM code. Do so
by specifying either ‘ld’ or ‘td’ as a second argument. For example:
>>> for num in find_rkm('sink200nA'):
... print(num)
200 msink

>>> for num in find_rkm('sink200nA', 'ld'):
... print(num)
200 nA

Pin Name Generator Example
As a practical example of the use of RKM codes, imagine wanting a program that
creates pin names for an electrical circuit based on a naming convention. It
would take a table of pin characteristics that are used to create the names.
For example:
>>> from quantiphy import Quantity
>>> from rkm_codes import to_rkm, set_prefs as set_rkm_prefs

>>> pins = [
... dict(kind='ibias', direction='out', polarity='sink', dest='dac', value='250nA'),
... dict(kind='ibias', direction='out', polarity='src', dest='rampgen', value='2.5μA'),
... dict(kind='vref', direction='out', dest='dac', value='1.25V'),
... dict(kind='vdda', direction='in', value='2.5V'),
... ]
>>> set_rkm_prefs(map_sf={}, units_to_rkm_base_code=None, show_units=True, prec=2)

>>> for pin in pins:
... components = []
... if 'value' in pin:
... pin['VALUE'] = to_rkm(Quantity(pin['value']))
... for name in ['dest', 'kind', 'direction', 'VALUE', 'polarity']:
... if name in pin:
... components.append(pin[name])
... print('_'.join(components))
dac_ibias_out_250nA_sink
rampgen_ibias_out_2uA5_src
dac_vref_out_1V25
vdda_in_2V5

Releases

Latest development release:

Version: 0.6
Released: 2023-04-14

0.6 (2023-04-14):

Suppress rkm_code’s use of the new SI scale factors in QuantiPhy so that R is no longer treated as
a scale factor when using the latest version of QuantiPhy.

0.5 (2020-02-01):

Allow argument to to_rkm() to be a string or simple number
Added strip_code preference
With small numbers show 0 rather than exponent

0.4 (2019-08-29):

added find_rkm()

0.3 (2019-08-23):

move the units to the middle of the number with the scale factor
added support for signed numbers
added show_units, strip_zeros, minus_sign, and prec to preferences
this release is not backward compatible; units at the end of the number
are no longer supported

0.2 (2018-09-14):

fixed issue in set_prefs()

0.1 (2018-09-12):

initial release