98
votes
Accepted
Duracell PowerCheck - How Does It Work?
According to the German Duracell website:
As you press the points, a current will flow through a metal strip getting warm. The display is a thermochromatic one. So the increased temperature will ...
- 17.9k
54
votes
Accepted
Why is the voltage measurement of this circuit different when the switch is on?
First of all, well done for doing the practical experiment. It's good to see people trying things and wanting to discover the answers to their observations.
It may be easier to visualise this with a ...
- 12.1k
37
votes
Measure voltage with no current
Neat physics solutions aside, the practical way to do this is with a very low input bias current op-amp running in a buffer configuration. One of these op-amps with a properly designed layout can draw ...
- 3,774
37
votes
Accepted
Determine voltage drop over 10G resistors with cheap multimeter
Do what the ancients did ==== use a Wheatstone bridge. Like this
simulate this circuit – Schematic created using CircuitLab
Rotate the 10,000 ohm potentiometer for ZERO reading.
Then measure ...
- 34.6k
36
votes
Circuit for measuring high voltage DC voltage (up to 1000V)
A resistor divider will do what you want, but at this voltage there are some issues you can normally ignore:
The top resistor has to be able to handle 1 kV. Those are harder to get than "ordinary" ...
- 314k
28
votes
Accepted
Why does battery voltage slowly return to the open voltage?
The main reason is the time it takes for the active chemicals in the cell to diffuse into the electrodes and reaction products of the chemical reactions to disperse.
The active chemicals are consumed ...
- 33.8k
27
votes
Accepted
Can anyone identify this circut?
If you sum the capacitors to just one, then it looks like an envelope detector.
If you put capacitors in parallel then you can sum them together to just one.
$$C_{tot}=C_1+C_2+C_3+C_4$$
And then you ...
- 8,239
23
votes
Why is the voltage measurement of this circuit different when the switch is on?
This is an extremely nice experiment!
I have an idea to add to jonk's comment:
It is super-good that you are testing out what happens like this! As already provided, the answer is that the battery ...
- 98.3k
23
votes
Accepted
How do I know if a wire is floating or not?
So what tool/method should i use to check if wire is floatinf?
Measure the voltage when the pin is pulled to Vcc by a high value resistor, like 100K.
Make the same measurement when the pin is pulled ...
- 5,027
22
votes
Accepted
How to read 0 -10V analog voltage with lower voltage tolerant ADCs without a voltage divider
However because this is for a prototype that should be up to Industrial safety standards, my boss wants me to isolate the 10V from the 3.3V logic.
I question your boss's logic when it comes to ...
- 98.3k
21
votes
Accepted
Reasons not to use these leads
In addition to the excellent answer given by @JorenVaes there is also a simpler electro mechanical reason for this caution. If you take a close look at the lead connections for the 34xxxA multimeters ...
- 57.6k
21
votes
Why is my 50-600V voltage tester able to detect 3V?
plugging it into a 120V outlet means there should be a 3V drop across each bulb, so my 50-600V tester shouldn't be able to detect that
Your tester is not detecting the voltage drop across a bulb, but ...
- 33.6k
19
votes
Accepted
Does an oscilloscope subtract voltages as phasors?
The math subtraction function in an oscilloscope subtracts the instantaneous values of waveform 1 from the instantaneous values of waveform 2 to create a new waveform comprising all those ...
- 467k
19
votes
Accepted
What does the horizontal bar indicate in the DMM display?
That bar at the bottom of the screen simulates an analog meter - the length of the bar increases with increasing digital readings. It is often easier to observe a varying voltage by looking at the ...
- 60.2k
16
votes
How do I measure a voltage greater than 5 V with Arduino?
Step down the voltage with a resistive divider and buffer it with an rail-to-rail input and output op-amp wired up as a voltage follower. This buffers the resistance in the resistive divider from the ...
- 57k
16
votes
Are there any tricks for measuring high voltages (~1000 V) efficiently?
Battery powered designs prefer voltage dividers with large resistance values. ADCs want low output impedances. An expedient way to lower the output impedance of a resistive divider is to add a ...
- 38.5k
15
votes
Reasons not to use these leads
The 3458A is an 8 1/2 digit, calibration/metrology grade instrument. When measuring 1V, your least significant digits will be nanovolts. At this level of accuracy, you need to pay attention to ...
- 12.6k
15
votes
Accepted
Is it normal for a lithium ion battery to read with a very low voltage on a multimeter?
Almost any charging circuit for Lithium batteries has a low voltage protection built in. This will protect against charging dead batteries (which might overheat) and this also inhibits enabling the ...
- 3,231
15
votes
Accepted
Can I use capacitor to measure time?
Yes, this is a well-established method of measuring with resolution in the picoseconds without requiring impossibly high clock frequencies. You switch a current source to a capacitor.
The generic term ...
14
votes
Measuring a small resistance, ~0.001 ohm
You can't "accurately determine" such a low resistance using household DMMs, which are likely completely lack of any calibration whatsoever. Accuracy class of your household DMMs is way worse than 1%, ...
- 41.8k
14
votes
What does the horizontal bar indicate in the DMM display?
From the Fluke 87V datasheet page 11 point 18 :
The number of segments is relative
to the full-scale value of the
selected range. In normal operation
0 (zero) is on the left. The polarity
...
- 1,297
14
votes
What does the horizontal bar indicate in the DMM display?
The bar is a fast-responding 'analog meter', that can be useful for following variations in the input voltage, for instance when you're adjusting a circuit with a potentiometer in real time.
In the ...
- 171k
14
votes
Accepted
What is the voltage drop across the 10 ohm resistor?
Millman's theorem is a kind of multi source voltage divider theorem based on this topology: -
So, re-arrange your circuit to use a 3rd source that is actually 0 volts and you're good to go: -
Hence \...
- 467k
14
votes
Accepted
Measuring high voltage with a microcontroller
simulate this circuit – Schematic created using CircuitLab
The resistors divider works always exactly the same. For very precise measurement you need a low TCR value resistors. The tolerance ...
- 24.2k
13
votes
Accepted
How to improve resolution and precision of sensor reading?
Sorry for my poor explanation and English.
There are a number of important terms in English. But these would have the same scientific meaning in any language. So you'll need to work out the mental &...
- 78.4k
13
votes
Does an oscilloscope subtract voltages as phasors?
The algebra of phasors is valid only for time invariant sinusoids of same frequency. You can't apply algebraic functions on phasors whose sinusoids do not have the same frequency.
Thus your ...
- 885
13
votes
Accepted
Audio Jack Safety 230v DC
This should absolutely not be used above ~20-30 volts, and even that's pushing it.
One of the main problems with T(R*)S connectors is that, when inserting or removing the plug, the contacts are ...
- 36.3k
13
votes
How to read 0 -10V analog voltage with lower voltage tolerant ADCs without a voltage divider
I would use an opto-coupler if this was a digital signal, but I am not sure if there is a way to achieve the same level of isolation while reading analog values.
There is a product sold as a "...
- 132k
13
votes
Accepted
Voltage drop over open circuit
The meter has some high resistance across its terminals (in the megaohm range for a DMM, about 10k to 50k for an analog meter type) so a slight current will flow through it, the LED and the resistor.
...
- 56k
Only top scored, non community-wiki answers of a minimum length are eligible