Plain text component values

[endolith]

Hi, I made this for parsing plain text schematic values:

https://gist.github.com/endolith/1a74477fc1659cd6bf9d138e09c72672

value_parser('100 MΩ')
Out[194]: (100000000.0, u'ohm')

value_parser('2M2')
Out[195]: (2200000.0, None)

value_parser('4n7')
Out[196]: (4.700000000000001e-09, None)

value_parser('4.7 nH')
Out[197]: (4.700000000000001e-09, u'henry')

So you could make entering components more readable and catch mistakes more easily, too:

cir.add_resistor('R1', 'n1', 'n2', '50 ohm')
cir.add_inductor('L1', 'n2', 'n3', '245.894m')
cir.add_capacitor('C1', 'n3', 'n4', '103.013 nF')
cir.add_inductor('L2', 'n4', cir.gnd, '98.3652 μH')
cir.add_vsource('V1', 'n1', cir.gnd, dc_value='0 V'., ac_value='1 V')

Is this something you'd be interested in incorporating?

For instance in Circuit.add_resistor, it would be something like this:

value, unit = value_parser(value)
if unit not in {None, 'ohm'}:
    raise Exception('Unit doesn't match component type')
if value == 0:
    raise CircuitError("ZERO-valued resistors are not allowed.")

or put the exception inside the function:

value = value_parser_and_checker(value, should_be='ohm')
if value == 0:
    raise CircuitError("ZERO-valued resistors are not allowed.")

So entering units would be optional, but would help catch errors of changing the wrong value, etc. I think most SPICE implementations ignore units.

[itdaniher]

Hey there! Somehow this originally fell threw the cracks in my inbox, but the improvement looks great and I'd love to figure out how to get it merged!

[itdaniher]

Thinking about this further:

I like

value = value_parser_and_checker(value, should_be='ohm')
if value is None:
    raise CircuitTypeError("Circuit components need to have nonzero values)

This way, I think we have a utility function to add, which you already wrote, and hooks to add to the __init__ methods of the relevant classes, or, less generally, in the Circuit.add_foo methods for each circuit element.

Personally, I'd move even the existing if value == 0 check into the __init__ calls for each circuit element, as they're only implemented for a few select components, and it might be worth adding sanity checks that keep someone from trying to simulate the transient response of a circuit with a 1 megafarad capacitor and a 1 megaohm resistor, or other equally awkward unit-ed component combinations.

[itdaniher]

We already have more infrastructure for this than I realised, as G took the initiative to work towards SPICE syntax compatibility!

http://ahkab.readthedocs.io/en/latest/netlist_parser.html?highlight=convert_units#ahkab.netlist_parser.convert_units

Found just reading netlist_parser thinking about unicode units.....

[endolith]

SPICE annoyingly equates M with "milli", when it means "mega" everywhere else. Also what is mil = 25.4x1e-6 for? PCB dimensions?

Anyway the intent was for this to be for the pythonic API, not SPICE.