Voltage Drop at Breadboard

[tggzzz]

A point to bear in mind when using or not using breadboards: Sometimes signal integrity and layout doesn't actually matter that much!

I'm doing some sub 1KHz stuff with opamps at the moment which requires a lot of trial and error. I'm doing it on a 3M breadboard and am giving zero fucks

Yup.

A 1kHz analogue signal isn't going to have much energy above 100MHz. A 1kHz digital signal would, though.

The other issues with analogue circuits are that that although your signal may only be 1kHz, it is quite possible for the circuit elements to have much higher frequency response. Remember the old adage: "amplifiers oscillate, oscillators don't"

[tggzzz]

I was not sure what more information another 6 inches of wire would add, after all, there is already ~425mm of conductor including 8 wire to board insertions, but I looked at it anyway.






I don't actually see much difference.

While I was at it, I measured the resistance of one 425mm length of breadboard rails (plus wire jumpers) at 18 ohms. If I did the math right, this agrees closely with the 40 mV voltage drop I recorded previously. The capacitance across the pair of rails (all 425mm) was measured as about 85 pF.

That's still a well-controlled slow risetime, unlike that seen with jellybean logic. Even with that signal, you can see some oscillation at ~100MHz.

I don't know how 100MHz compares with your scope's bandwidth, but a 100MHz signal on a 100MHz scope+probe would be 3dB down, i.e. only 70% of the actual amplitude.

[bd139]

A point to bear in mind when using or not using breadboards: Sometimes signal integrity and layout doesn't actually matter that much!

I'm doing some sub 1KHz stuff with opamps at the moment which requires a lot of trial and error. I'm doing it on a 3M breadboard and am giving zero fucks

Yup.

A 1kHz analogue signal isn't going to have much energy above 100MHz. A 1kHz digital signal would, though.

The other issues with analogue circuits are that that although your signal may only be 1kHz, it is quite possible for the circuit elements to have much higher frequency response. Remember the old adage: "amplifiers oscillate, oscillators don't"

Indeed.

I've seen a 2n3904 oscillating well into VHF (190MHz) on a breadboard. I assume it was due to the breadboard stray capacitance and collector wire inductance acting as a colpitts style oscillator. I played with it for a bit to see if I could tune it then gave up and shut it up by leveraging the miller effect with a 47pF across collector/base. I was establishing DC operating point of a circuit before I moved it in situ on a manhattan construction board.

[tggzzz]

Quote from: rdl on Today at 12:55:08 am

One more thing, and this is something that I've previously seen evidence of potentially being a real problem. This image is where the crosstalk is looked at on the long 425mm path. The blue trace is the actual signal on the "positive" rail (red jumpers), and the yellow is the induced signal on the "negative" (black jumpers) rail.

>

Here the same signal is running through one of the five hole vertical strips (blue trace) with the crosstalk that appears on the adjacent five hole socket strip (yellow trace). Doesn't look that bad actually.



I'd like to point out to anyone reading this thread that running a 10MHz signal through 425mm of conductor, including multiple wire to board insertion connections, is somewhere beyond "worst case scenario". I'm sure decent quality breadboards have a limit to their usefulness, but I don't know where it is and I'm not inclined to go looking today.

I'm not entirely sure what you are showing there, since the detailed wiring matters.

However, NEXT and FEXT on signals can be serious problems. (NEXT= near end crosstalk, FEXT= far end crosstalk). But I doubt the traces show those.

More important is ground bounce, which does cause serious problems even on well-laid out multilayer PCBs. It is one of the reasons that modern busses tend to be serial rather than the old-time parallel busses.

Do the calculation using, say, a 3V signal swing with a 10pF load capacitance and a 2ns transition time, and a 6inch/150nH wire:

• current i_c required to charge a capacitor C through a voltage dV in time dt is i_c= C ^dV/_dt, so i_c = 15mA
• voltage V_i induced across a capacitor by a changing current dI in time dt is  V_i = L ^dI/_dt, so V_i = 1.125V
• and you can multiply that by however many outputs are changing simultaneously!

Obviously you can play around with the precise numbers until the cows come home, but having a +-1V signal "suddenly" appear on the ground/Vcc line isn't going to lead to operation within the IC's specification.

[rdl]

I'm not entirely sure what you are showing there, since the detailed wiring matters.

[tggzzz]

I'm not entirely sure what you are showing there, since the detailed wiring matters.

I don't see what the lower scope probe's shield is connected to.

I expect the solderless breadboard has wide internal connections, in which case they will have a lower inductance than a wire of the same length.

[rdl]

I don't see what the lower scope probe's shield is connected to.

It was connected to the same place on the resistor as the other probe and function generator when the screenshot was taken. I had disconnected it and was probing around at various places on the breadboard to see where and how much of the signal I could pick up. The induced signal was about 500 mV larger with the scope ground disconnected.

[Jwillis]

I did an experiment to find the resistance of of a bread board compared a piece of wire and trace of a PCB.Its a simple test with a moderately priced mOhm meter , a typical inexpensive 170 mm breadboard with 145 mm rails , 145 mm of AWG 26 wire (typical breadboard wire I use) and 145 mm 1mm wide trace of 1oz PCB.This was done at or as close as possible to the same temperature of 20 C. And Zeroing calibration was done between each test.
The results were not really surprising but interesting non the less .The bread board 145mm rail had a resistance of 46.5 mOhms .The 145mm  26AWG wire had a resistance of 40.2 mOhms . Trace 1mm on the 1 oz PCB showed a 120 mOhm resistance.
All conductive surfaces will exhibit a resistance .And this resistance will increase with distance the narrower the path and increases in ambient temperature.This is unavoidable. If your expectations don't include this unavoidable  variable then your project is beyond the realm of conventional conductors and  into superconductors.
Keep your paths as short as possible when prototyping your design regardless if you use a breadboard or PCB proto-board. 

[iMo]

FYI - the capacitance between the 5pin segments is 3.5pF.

[tggzzz]

I did an experiment to find the resistance of of a bread board compared a piece of wire and trace of a PCB.Its a simple test with a moderately priced mOhm meter , a typical inexpensive 170 mm breadboard with 145 mm rails , 145 mm of AWG 26 wire (typical breadboard wire I use) and 145 mm 1mm wide trace of 1oz PCB.This was done at or as close as possible to the same temperature of 20 C. And Zeroing calibration was done between each test.
The results were not really surprising but interesting non the less .The bread board 145mm rail had a resistance of 46.5 mOhms .The 145mm  26AWG wire had a resistance of 40.2 mOhms . Trace 1mm on the 1 oz PCB showed a 120 mOhm resistance.

And what was the variation in the resistance (a) with different (diameter, oxidation, dirt) wires (b) with different holes (c) when something was dropped nearby on the bench (d) tomorrow?

Often the absolute value isn't too important, but stability and predictability is important. I would expect soldered joints to be significantly better in that respect.

[Jwillis]

I did an experiment to find the resistance of of a bread board compared a piece of wire and trace of a PCB.Its a simple test with a moderately priced mOhm meter , a typical inexpensive 170 mm breadboard with 145 mm rails , 145 mm of AWG 26 wire (typical breadboard wire I use) and 145 mm 1mm wide trace of 1oz PCB.This was done at or as close as possible to the same temperature of 20 C. And Zeroing calibration was done between each test.
The results were not really surprising but interesting non the less .The bread board 145mm rail had a resistance of 46.5 mOhms .The 145mm  26AWG wire had a resistance of 40.2 mOhms . Trace 1mm on the 1 oz PCB showed a 120 mOhm resistance.

And what was the variation in the resistance (a) with different (diameter, oxidation, dirt) wires (b) with different holes (c) when something was dropped nearby on the bench (d) tomorrow?

Often the absolute value isn't too important, but stability and predictability is important. I would expect soldered joints to be significantly better in that respect.

Indeed its a static experiment .It wasn't meant to include other unforeseen variations as you describe.But it does have conclusive evidence that the rails resistance is not much more than a piece of wire yet much less than a PCB .Breadboards are not intended to be used as a final construction and I would agree that they have their own inherent draw backs .But soldering ,desoldering and resoldering over and over can have its own inherent draw backs as well .Component damage and wasted resources being at the top. Bread boards ,as mentioned before, have been used for years and years for experimentation prior to prototyping.Although today there are simulators but they have limitations as well like variations in component performance that may not seem apparent until a rough mock-up is put to a test. 
If some feel that the use of a breadboard is not in their best interest for experimentation so be it.The majority list them as one useful tool essential to experimentation.But like any tool proper use and maintenance  is important as well.
   

[rdl]

I did an experiment to find the resistance of of a bread board compared a piece of wire and trace of a PCB.Its a simple test with a moderately priced mOhm meter , a typical inexpensive 170 mm breadboard with 145 mm rails , 145 mm of AWG 26 wire (typical breadboard wire I use) and 145 mm 1mm wide trace of 1oz PCB.This was done at or as close as possible to the same temperature of 20 C. And Zeroing calibration was done between each test.
...

Your measurements are not too different from mine, yet the op was seeing more than an order of magnitude higher voltage drop. It seems there almost has to be something not right with either his board or the connections.

[Jwillis]

More information on the step down converter might help. I would guess that its not preforming as required.Although so many amps may be supplied to it does not mean that's what you'll get out.Even small amounts of resistance can cause voltages to drop out when theirs not enough current supplied.Any circuit will only draw as much current it requires .But if the current isn't there the voltage will drop. 

[tooki]

Your measurements are not too different from mine, yet the op was seeing more than an order of magnitude higher voltage drop. It seems there almost has to be something not right with either his board or the connections.

Definitely. As I said earlier, I've got a few chinesium breadboards that have several ohms (!) contact resistance. (And many more that are just fine, in the dozens of mOhms like yours.) I've marked the bad ones. They're OK for really simple stuff like testing LEDs, but I don't use them for any real circuits. I suspect the OP has a similar issue.

Additionally, some of those chinese "dupont" jumpers have poor connections or wire, and have excessive resistance, too.

[Ian.M]

Can you test your crappy chinesium breadboards with a magnet?  It would be interesting to find out if the problems with them are due to the use of steel contact strips.

[tooki]

Can you test your crappy chinesium breadboards with a magnet?  It would be interesting to find out if the problems with them are due to the use of steel contact strips.

Just checked, does not appear to be magnetic at all.

[rdl]

I have a lot of breadboards I've acquired over the last 30 years or so. There are quite a few I would describe as cheap junk, but only one is magnetic. It's a green mini size one that I had added my last ebay order of cheap stuff from China just to see if it was any good.

https://www.ebay.com/itm/5-Color-Mini-Solderless-Prototype-Breadboard-170-Tie-points-For-Arduino-Shield/201677166530

[Jwillis]

I only have one that I know is from China the rest are from North American suppliers with unknown origin.I tend to be a cheap son of a gun because my just a hobbyist.But non exhibit magnetic properties and all have similar resistance of approximately  0.5 - 1 mOhm between each socket.But magnetism might not be conclusive either because they may have nickel plating.
I suppose my next order from Digikey I'll breakdown for a brand name one and see if theirs a difference.
Aside from a few decade counters and timers most of what i do is mostly power electronics so my experience is admittedly limited.But I would definitely check that convertors output.