4 ms·

I wonder if it models the terrible parasitics of a real breadboard. I imagine it would be really annoying for beginners to build an IR receiver (or whatever) w

by mbell 13y ago

I wonder if it models the terrible parasitics of a real breadboard. I imagine it would be really annoying for beginners to build an IR receiver (or whatever) with the software, have it working perfectly, then try to build it on a real breadboard only to spend hours frustratingly trying to figure out why the circuit is oscillating.

toomuchtodo 13y ago
Is there any software out there that includes these real-world models into the design side?
- mbell 13y ago
  Yes, but its usually not worth the time to include all parasitics in a model until you get to very high frequency work. Professional circuit/PCB designers already know roughly what the issues are going to be and can order of magnitude approximate well enough to know if its worth fully modeling or not. For novices, just understanding what the parasitics are is hard enough, much less adding them to a circuit that is often already fairly complicated for them. Most lower frequency stuff that novices will be building should not have an issue with parasitics, but pushin breadboards are just awful and the most common hobbyist op amps have plenty high enough gain-bandwidth-products to bring them into play.
- fnordfnordfnord 13y ago
  Umm, Spice[1]? I don't have a good model for a rusty piece of tin, but maybe someone does. [1] Like all cheapskates, I use LTSpice.
- nanospider 13y ago
  Yes, you can use something like AWR or ADS. Although they cost megabucks.
- compumike 13y ago
  mbell is right -- rather than just adding parasitic capacitance and inductance estimates to every node, it's more helpful for the engineer to be able to evaluate and discover which nodes are particularly sensitive and which aren't. Start with some back-of-the-envelope order-of-magnitude estimates (maybe guess ~1nH/mm inductance for a wire, ~1pF capacitance between adjacent pins), and an experienced engineer will already be able to eyeball likely trouble spots in your circuit. The novice can certainly use the same concepts with simulation to do quite a bit of "debugging" in just a few minutes, for example dragging around a 1pF cap between a bunch of pins, re-running the simulation each time, and seeing where it has the most detrimental effect on an analog circuit.
  - mbell 13y ago
    Just to add, if you want to 'fail safe' a breadboard design, your better off assuming ~25pF of stray capacitance per breadboard insertion point. You should also make sure your circuit bandwidth is less than ~8-10Mhz, keeping in mind that if you have an opamp with GBP of 20Mhz and you're using it with a gain of 2, you may have a problem. Stray inductance can also play a part, but it's far less likely.
fein 13y ago
You can always measure the capacitance between each row. Hell of a lot better than building a full circuit first, just to find out your BB sucks.
- mbell 13y ago
  That usually doesn't help as a large source of the problematic parasitics is contact between the part's leads and the 'grippers' inside the breadboard. Lead diameter, corrosion, 'gripper' spring strength, etc all come into play there.
  - jonmrodriguez 13y ago
    So if it's so random that you can't reliably measure it because it changes every time you plug and unplug the same pin (let alone different pin diameters), how can software hope to model it?
    - stephengillie 13y ago
      Each time you virtually plug something in the program's breadboard, generate a random number. If the number is lower than a threshold, prevent the connection from working. Change the threshold at every program loading and randomly during use.
      - jonmrodriguez 13y ago
        Haha I assume you're joking; that would give the user zero benefit and immense pain.
    - mbell 13y ago
      When I say 'model it', I mean that loosely, perfect modeling of electronics circuits isn't realistic anyway, any modeling worth the effort will assume a range of possible values for anything under test. A simple example would be if the software warned the user that an active filter design was dangerously close to instability and thus had a decent chance of oscillating when real world parasitics are present.
Brashman 13y ago
Welcome to EE lab. In one lab as an undergrad, my partner and I found that we could get our circuit to work by attaching a capacitor with one end to our circuit and one end to a random place on the breadboard. It made for a bit of a funny circuit diagram in the write-up where one end of this capacitor was connected to nowhere.
- harrytuttle 13y ago
  Ex EE here (RF/mixed signal). I always modelled it as everything being connected to everything via a tiny capacitor and a big resistor in parallel. This allowed a few odd scenarios to be reliably identified, especially in UHF frequencies and above. The trailing capacitor just had a large value invisible resistor attaching it to your circuit somewhere :)

by mbell 13y ago

toomuchtodo 13y ago

Is there any software out there that includes these real-world models into the design side?

mbell 13y ago
Yes, but its usually not worth the time to include all parasitics in a model until you get to very high frequency work. Professional circuit/PCB designers already know roughly what the issues are going to be and can order of magnitude approximate well enough to know if its worth fully modeling or not. For novices, just understanding what the parasitics are is hard enough, much less adding them to a circuit that is often already fairly complicated for them. Most lower frequency stuff that novices will be building should not have an issue with parasitics, but pushin breadboards are just awful and the most common hobbyist op amps have plenty high enough gain-bandwidth-products to bring them into play.
fnordfnordfnord 13y ago
Umm, Spice[1]? I don't have a good model for a rusty piece of tin, but maybe someone does. [1] Like all cheapskates, I use LTSpice.
nanospider 13y ago
Yes, you can use something like AWR or ADS. Although they cost megabucks.
compumike 13y ago
mbell is right -- rather than just adding parasitic capacitance and inductance estimates to every node, it's more helpful for the engineer to be able to evaluate and discover which nodes are particularly sensitive and which aren't. Start with some back-of-the-envelope order-of-magnitude estimates (maybe guess ~1nH/mm inductance for a wire, ~1pF capacitance between adjacent pins), and an experienced engineer will already be able to eyeball likely trouble spots in your circuit. The novice can certainly use the same concepts with simulation to do quite a bit of "debugging" in just a few minutes, for example dragging around a 1pF cap between a bunch of pins, re-running the simulation each time, and seeing where it has the most detrimental effect on an analog circuit.
- mbell 13y ago
  Just to add, if you want to 'fail safe' a breadboard design, your better off assuming ~25pF of stray capacitance per breadboard insertion point. You should also make sure your circuit bandwidth is less than ~8-10Mhz, keeping in mind that if you have an opamp with GBP of 20Mhz and you're using it with a gain of 2, you may have a problem. Stray inductance can also play a part, but it's far less likely.

fein 13y ago

You can always measure the capacitance between each row. Hell of a lot better than building a full circuit first, just to find out your BB sucks.

mbell 13y ago
That usually doesn't help as a large source of the problematic parasitics is contact between the part's leads and the 'grippers' inside the breadboard. Lead diameter, corrosion, 'gripper' spring strength, etc all come into play there.
- jonmrodriguez 13y ago
  So if it's so random that you can't reliably measure it because it changes every time you plug and unplug the same pin (let alone different pin diameters), how can software hope to model it?
  - stephengillie 13y ago
    Each time you virtually plug something in the program's breadboard, generate a random number. If the number is lower than a threshold, prevent the connection from working. Change the threshold at every program loading and randomly during use.
    - jonmrodriguez 13y ago
      Haha I assume you're joking; that would give the user zero benefit and immense pain.
  - mbell 13y ago
    When I say 'model it', I mean that loosely, perfect modeling of electronics circuits isn't realistic anyway, any modeling worth the effort will assume a range of possible values for anything under test. A simple example would be if the software warned the user that an active filter design was dangerously close to instability and thus had a decent chance of oscillating when real world parasitics are present.

Brashman 13y ago

Welcome to EE lab. In one lab as an undergrad, my partner and I found that we could get our circuit to work by attaching a capacitor with one end to our circuit and one end to a random place on the breadboard. It made for a bit of a funny circuit diagram in the write-up where one end of this capacitor was connected to nowhere.

harrytuttle 13y ago
Ex EE here (RF/mixed signal). I always modelled it as everything being connected to everything via a tiny capacitor and a big resistor in parallel. This allowed a few odd scenarios to be reliably identified, especially in UHF frequencies and above. The trailing capacitor just had a large value invisible resistor attaching it to your circuit somewhere :)