6 ms·

It is just a pet peeve of mine (disclosure, I am a terminally degreed engineer), but it is something a lot of non-EE people forget: circuits do not "push" curre

It is just a pet peeve of mine (disclosure, I am a terminally degreed engineer), but it is something a lot of non-EE people forget: circuits do not "push" current, your wall outlet does not "push amps" and this applies to micro-electronics (as well as pico, nano, fempto, etc)... the circuit is always a combination of the source and load. So, if the load is not equal to the source (or vice versa, does not matter), by conservation of energy, we have some "leftover"... in signals, this leftover is going to travel back from whence it came, causing (possibly) attenuation or amplification depending on timing, which some might call distortion. It can be tricky to keep this in mind when you are working with complex circuits, and it gets more difficult as speeds increase and signal sizes go down.

jacquesm 3y ago
A good real world example is fluid flow such as a gas compressed through a pipe, say a trumpet or an exhaust. If the standing wave in the pipe isn't optimal at the exit of the pipe a part of the energy will end up reflected which causes a very real obstruction and higher pressure. In a trumpet this manifests as a resonant filter that will leave all but a couple of frequencies without significant damping and that is the note (+ overtones) that you hear. In an exhaust such tuning will result in the system performing optimally at certain RPMs, and if you match that to when you want the engine to produce maximum power you can create a peak by get rid of the exhaust gases at that peak. Hence resonant exhaust systems tuned to the theoretical peak of an engine.
- alfiedotwtf 3y ago
  That's a cool analogy! I wonder if the exhaust could by dynamic i.e change length depending on the RPMs
  - teeray 3y ago
    Many antennas do this (screwdriver antennas come to mind), so I’d expect some similar ability to do this with exhaust. The only issue I can think of is turbulence from the seams of segments that extend.
  - jacquesm 3y ago
    The answer is: yes. The results: 6% gain or thereabouts with a fairly impressive amount of extra complexity. But it can be done. https://www.researchgate.net/publication/322390752_Continuously_Varying_Exhaust_Pipe_Length_and_Diameter_to_Improve_the_Performance_of_a_Naturally_Aspirated_SI_Engine https://www.researchgate.net/publication/322390752_Continuou...
  - function_seven 3y ago
    Way back when Jet Skis had 2-stroke engines, you could buy an aftermarket exhaust pipe with water injection in a couple key spots. This allowed the pipe to be dynamically tuned to different RPMs by changing the speed of sound within the pipe. The stock pipe was tuned to a specific RPM, allowing the reflected exhaust pulse to return to the cylinder just as the port was closing and “slam the door” on the fresh air/fuel charge. With variable water injection, you could have more than one optimal RPM. (All this is from memory as I read the ads in Splash magazine.)
    - jacquesm 3y ago
      Oh that's so clever, to use the water that is there anyway as a means of affecting the dynamics of the pipe. Whoever came up with that was on another level.
- jiveturkey 3y ago
  > real world example electric/electronic circuits operate in the real world. mechanical example is what you're after.
- pests 3y ago
  Here is a YouTuber who is making a physically based audio engine using fluid dynamics (demos so far for various engines, a trumpet, a steam whistle, dev videos) https://www.youtube.com/channel/UCV0t1y4h_6-2SqEpXBXgwFQ https://www.youtube.com/channel/UCV0t1y4h_6-2SqEpXBXgwFQ A lot of what you wrote reminded me of what he is working on - the trumpet sim is not entirely accurate yet but watching those reflections bounce and forth like you describe is very interesting. Trumpet Video: https://www.youtube.com/watch?v=rGNUHigqUBM&t=87s https://www.youtube.com/watch?v=rGNUHigqUBM&t=87s
  - jacquesm 3y ago
    That's amazing, incredible programming and analysis skills on display there.
bee_rider 3y ago
I didn’t get a terminal EE degree (it is more fun to tell the magic smoke what to do, than try and keep it in the chip), but you can of course design a circuit that will adjust voltage to keep current constant (within some bounds, etc etc). Could that not reasonably be said to be “pushing current”?
- dragontamer 3y ago
  If there's no inductor (and inductors are dangerous: see my other comment), then nothing on that PCB is pushing any current. Its all illusions created by "pulling" current. > but you can of course design a circuit that will adjust voltage to keep current constant So there's two designs and they're different in important ways. But first: the common part of _both_ designs is that the transistor is working as a "controlled resistor". The question is where you place this special resistor. The other commonality is that "negative-feedback" can configure this transistor to reach the appropriate resistance very easily. So with the common stuff out of the way: we have two designs. "Series Regulator" and "Shunt Regulators" (traditionally voltage-regulators, but they could be current in practice. I'll discuss as if they're current regulators). 1. Series Regulator -- The transistor is treated as an adjustable resistor "in series" with the rest of the circuit. This "pinches down" the voltage/current to the level deemed acceptable to the engineer. Ex: If "downstream", you sense a 100-Ohm load and you have a target-current of 10mA, and your source voltage is 5V, you set the transistor so that its equivalent to 400-Ohms (total a 500-ohm system, so 10mA goes through). But if the downstream circuit changes (a button was pressed and a motor is now being driven), and the downstream circuit now looks like a 10-Ohm load, to keep the constant 10mA current your Series-Regulator will automatically set the transistor to act like a 490-Ohm resistor (keeping the 500-ohm system, so 10mA remains constant). 2. Shunt Regulator -- The transistor is treated as an adjustable resistor "in parallel" with the rest of the circuit. This "diverts" excess energy to ground, causing the rest of the circuit to effectively function within its specifications. Ex: If "downstream", you sense a 100-Ohm load and you have a target-current of 10mA and your source current is 50mA, you set the transistor so that it is equivalent to 25-Ohms. This shunts 40mA to ground, and the remaining 10mA goes to the 100-Ohm load. But if the downstream circuit changes (a button was pressed and a motor is now driven), and the downstream circuit now looks like a 10-Ohm load... to keep the constant 10mA current your Shunt-regulator will automatically set the transistor to act like a 2.5-Ohm load. This shunts 40mA to ground and the remaining 10mA goes to the 100-Ohm load. ----------- Traditionally, series and shunt regulators sense voltage (not current), but its not very difficult to turn a voltage-regulator into a current-regulator instead. Series regulators are your typical 7905 or whatever. They are more efficient (as you can tell by their obvious operation) and simpler to use. Shunt regulators are traditionally Zener Diodes, or other circuits that are based "like" a Zener Diode. They can generate constant voltage offsets reliably (ex: if you have a 9V line from a series regulator, and you need a 7V reference, you can use a shunt-regulator to very accurately create -2V). -------------- As you can see, its all "pulling tricks". Of course, the switching regulator (Ex: MC34063. Don't use, this is an old chip lol. But maybe TI's Simple Switcher series, or similar), truly "push" current thanks to an externally supplied inductor... and as a result lead to far superior efficiency specs. Another "pushing" trick is a charge-pump. You can turn on capacitors in such a way that they double the voltage. That's the thing about "pushing", you need an ability to increase voltage until the "downstream" circuit acts the way you like. Inductors (and capacitors, to a lesser extent) _can_ push. But its dangerous and somewhat difficult to design well. (Fortunately, we have pre-made modules like TI's Simple Switcher or Microchip's MCP1640, etc. etc. that do the job for us automatically... as well as pre-made power supplies).
dragontamer 3y ago
> circuits do not "push" current Except for inductors. See: Tesla coils. If you forget a snubbing diode on a large motor (which is very inductive), you'll likely see some fires on your PCB. Inductors (and inductive loads) will push current even if the other side doesn't want it (ex: even if the other side is a 10 Gig-ohm resistance, the current will continue and possibly spike the voltage to millions-of-volts and shoot lightning out to allow the inductor to keep pushing the current)
hatsunearu 3y ago
it's easier to think everything is a transmission line and everything is propagation with finite impedances rather than thinking everything is an idealized element and figuring out what the exceptions are.

jacquesm 3y ago

A good real world example is fluid flow such as a gas compressed through a pipe, say a trumpet or an exhaust. If the standing wave in the pipe isn't optimal at the exit of the pipe a part of the energy will end up reflected which causes a very real obstruction and higher pressure. In a trumpet this manifests as a resonant filter that will leave all but a couple of frequencies without significant damping and that is the note (+ overtones) that you hear. In an exhaust such tuning will result in the system performing optimally at certain RPMs, and if you match that to when you want the engine to produce maximum power you can create a peak by get rid of the exhaust gases at that peak. Hence resonant exhaust systems tuned to the theoretical peak of an engine.

alfiedotwtf 3y ago
That's a cool analogy! I wonder if the exhaust could by dynamic i.e change length depending on the RPMs
- teeray 3y ago
  Many antennas do this (screwdriver antennas come to mind), so I’d expect some similar ability to do this with exhaust. The only issue I can think of is turbulence from the seams of segments that extend.
- jacquesm 3y ago
  The answer is: yes. The results: 6% gain or thereabouts with a fairly impressive amount of extra complexity. But it can be done. https://www.researchgate.net/publication/322390752_Continuously_Varying_Exhaust_Pipe_Length_and_Diameter_to_Improve_the_Performance_of_a_Naturally_Aspirated_SI_Engine https://www.researchgate.net/publication/322390752_Continuou...
- function_seven 3y ago
  Way back when Jet Skis had 2-stroke engines, you could buy an aftermarket exhaust pipe with water injection in a couple key spots. This allowed the pipe to be dynamically tuned to different RPMs by changing the speed of sound within the pipe. The stock pipe was tuned to a specific RPM, allowing the reflected exhaust pulse to return to the cylinder just as the port was closing and “slam the door” on the fresh air/fuel charge. With variable water injection, you could have more than one optimal RPM. (All this is from memory as I read the ads in Splash magazine.)
  - jacquesm 3y ago
    Oh that's so clever, to use the water that is there anyway as a means of affecting the dynamics of the pipe. Whoever came up with that was on another level.
jiveturkey 3y ago
> real world example electric/electronic circuits operate in the real world. mechanical example is what you're after.
pests 3y ago
Here is a YouTuber who is making a physically based audio engine using fluid dynamics (demos so far for various engines, a trumpet, a steam whistle, dev videos) https://www.youtube.com/channel/UCV0t1y4h_6-2SqEpXBXgwFQ https://www.youtube.com/channel/UCV0t1y4h_6-2SqEpXBXgwFQ A lot of what you wrote reminded me of what he is working on - the trumpet sim is not entirely accurate yet but watching those reflections bounce and forth like you describe is very interesting. Trumpet Video: https://www.youtube.com/watch?v=rGNUHigqUBM&t=87s https://www.youtube.com/watch?v=rGNUHigqUBM&t=87s
- jacquesm 3y ago
  That's amazing, incredible programming and analysis skills on display there.

bee_rider 3y ago

I didn’t get a terminal EE degree (it is more fun to tell the magic smoke what to do, than try and keep it in the chip), but you can of course design a circuit that will adjust voltage to keep current constant (within some bounds, etc etc). Could that not reasonably be said to be “pushing current”?

dragontamer 3y ago
If there's no inductor (and inductors are dangerous: see my other comment), then nothing on that PCB is pushing any current. Its all illusions created by "pulling" current. > but you can of course design a circuit that will adjust voltage to keep current constant So there's two designs and they're different in important ways. But first: the common part of _both_ designs is that the transistor is working as a "controlled resistor". The question is where you place this special resistor. The other commonality is that "negative-feedback" can configure this transistor to reach the appropriate resistance very easily. So with the common stuff out of the way: we have two designs. "Series Regulator" and "Shunt Regulators" (traditionally voltage-regulators, but they could be current in practice. I'll discuss as if they're current regulators). 1. Series Regulator -- The transistor is treated as an adjustable resistor "in series" with the rest of the circuit. This "pinches down" the voltage/current to the level deemed acceptable to the engineer. Ex: If "downstream", you sense a 100-Ohm load and you have a target-current of 10mA, and your source voltage is 5V, you set the transistor so that its equivalent to 400-Ohms (total a 500-ohm system, so 10mA goes through). But if the downstream circuit changes (a button was pressed and a motor is now being driven), and the downstream circuit now looks like a 10-Ohm load, to keep the constant 10mA current your Series-Regulator will automatically set the transistor to act like a 490-Ohm resistor (keeping the 500-ohm system, so 10mA remains constant). 2. Shunt Regulator -- The transistor is treated as an adjustable resistor "in parallel" with the rest of the circuit. This "diverts" excess energy to ground, causing the rest of the circuit to effectively function within its specifications. Ex: If "downstream", you sense a 100-Ohm load and you have a target-current of 10mA and your source current is 50mA, you set the transistor so that it is equivalent to 25-Ohms. This shunts 40mA to ground, and the remaining 10mA goes to the 100-Ohm load. But if the downstream circuit changes (a button was pressed and a motor is now driven), and the downstream circuit now looks like a 10-Ohm load... to keep the constant 10mA current your Shunt-regulator will automatically set the transistor to act like a 2.5-Ohm load. This shunts 40mA to ground and the remaining 10mA goes to the 100-Ohm load. ----------- Traditionally, series and shunt regulators sense voltage (not current), but its not very difficult to turn a voltage-regulator into a current-regulator instead. Series regulators are your typical 7905 or whatever. They are more efficient (as you can tell by their obvious operation) and simpler to use. Shunt regulators are traditionally Zener Diodes, or other circuits that are based "like" a Zener Diode. They can generate constant voltage offsets reliably (ex: if you have a 9V line from a series regulator, and you need a 7V reference, you can use a shunt-regulator to very accurately create -2V). -------------- As you can see, its all "pulling tricks". Of course, the switching regulator (Ex: MC34063. Don't use, this is an old chip lol. But maybe TI's Simple Switcher series, or similar), truly "push" current thanks to an externally supplied inductor... and as a result lead to far superior efficiency specs. Another "pushing" trick is a charge-pump. You can turn on capacitors in such a way that they double the voltage. That's the thing about "pushing", you need an ability to increase voltage until the "downstream" circuit acts the way you like. Inductors (and capacitors, to a lesser extent) _can_ push. But its dangerous and somewhat difficult to design well. (Fortunately, we have pre-made modules like TI's Simple Switcher or Microchip's MCP1640, etc. etc. that do the job for us automatically... as well as pre-made power supplies).

dragontamer 3y ago

> circuits do not "push" current Except for inductors. See: Tesla coils. If you forget a snubbing diode on a large motor (which is very inductive), you'll likely see some fires on your PCB. Inductors (and inductive loads) will push current even if the other side doesn't want it (ex: even if the other side is a 10 Gig-ohm resistance, the current will continue and possibly spike the voltage to millions-of-volts and shoot lightning out to allow the inductor to keep pushing the current)

hatsunearu 3y ago

it's easier to think everything is a transmission line and everything is propagation with finite impedances rather than thinking everything is an idealized element and figuring out what the exceptions are.