Electronics > Beginners

Voltage Drop at Breadboard

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tggzzz:

--- Quote from: anbudroid on March 14, 2019, 06:31:22 am ---

--- Quote ---Digital waveforms are analogue signals, ones that are interpreted by the receiver as being digital signals. If the analogue waveforms don't meet the input specification, the receiver can misinterpret them.

--- End quote ---

 you are right sir , but beginners  are not play more than 10Mhz clock signals with breadboard. and most of the Arduino players are much below this level.

--- End quote ---

Sigh. That misapprehension never goes away.

My step generator has ~1MHz period, and has significant energy content above 1GHz. The period is completely irrelevant; the only thing that matters is the transition time.

If you want an anthropromorphic handwaving explantion, consider that when the signal has one edge, it doesn't "know" when the next edge is coming - it might be in 1ns, 1s, or never.

For a little theory and some practical demonstrations, see https://entertaininghacks.wordpress.com/2018/05/08/digital-signal-integrity-and-bandwidth-signals-risetime-is-important-period-is-irrelevant/

rdl:
Out of curiosity, tonight I wired up a little test. Using one of my 3M No. 318 boards I input about 5 volts at the left end of the upper rails, ran it across to the right side and down the vertical rails, then back to the left end of the lower rails, a distance of nearly 17" (about 430mm). Actually double that for the entire loop. This meant it also went through 4 jumper wire connections (22 gauge tinned solid copper wire).

With no load, there was virtually zero voltage drop, maybe 1 mV at most. With two 47 ohm resistors in parallel as load (210 mA measured) I got about a 40 mV drop. This was from measuring directly at the input to the breadboard vs. measuring directly across the resistors.

Just thought people might find that interesting. If I get a chance, I may send a square wave through and see what it looks like on the scope.

tggzzz:

--- Quote from: rdl on March 15, 2019, 04:40:59 am ---Out of curiosity, tonight I wired up a little test. Using one of my 3M No. 318 boards I input about 5 volts at the left end of the upper rails, ran it across to the right side and down the vertical rails, then back to the left end of the lower rails, a distance of nearly 17" (about 430mm). Actually double that for the entire loop. This meant it also went through 4 jumper wire connections (22 gauge tinned solid copper wire).

With no load, there was virtually zero voltage drop, maybe 1 mV at most. With two 47 ohm resistors in parallel as load (210 mA measured) I got about a 40 mV drop. This was from measuring directly at the input to the breadboard vs. measuring directly across the resistors.

--- End quote ---

Then try knocking the breadboard and generally moving it in ways that you would do when experimenting with a circuit. See if anything changes.

Wait a couple od days, and repeat.


--- Quote ---Just thought people might find that interesting. If I get a chance, I may send a square wave through and see what it looks like on the scope.

--- End quote ---

Measurement technique is important, so document the source characteristics, the scope, and how you connect those to the UUT.

rdl:
A couple of pictures to look at. The square wave from my function generator is pretty sad, but for comparison purposes it'll have to do for now.

10MHz square wave at entry to board (blue) and at 47ohm resistor load 17" away (yellow)



20Khz sine wave (same situation, blue at entry, yellow at load)



I'll add this in case my previous description wasn't clear.



The voltages measured previously were at A and B across the rails. The signals are compared between points A and B. The resistor (47 ohm) was connected to the negative rail, not disconnected as in the picture. Two resistors in parallel were used for the voltage measurements.


tggzzz:
14ns risetime <=> 25MHz bandwidth, so your scope isn't the limiting factor.

I suggest you look at the output of a logic signal. For bonus points, insert two 6" breadboarding leads in between the scope/signal and scope/ground. The 15pF scope probe tip capacitance is similar to a couple of CMOS/TTL loads.

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