Hi Guys, Newb here:
In this circuit, I tried to measure the voltage between pin 2 (digitalread) and the 5v source.
With the multimeter in place as shown, the meter reads 5v with the button closed, 0v open, as expected.
However, the button no longer triggers the digitalread on pin 2 to HIGH.
What is the reason for this?
Because you have the meter connected incorrectly.
You have the meter connected to read current and set to measure voltage.
The black lead should be connected to ground, the read lead connected to pin 2 along with the switch and resistor.
adwsystems:
Because you have the meter connected incorrectly.You have the meter connected to read current and set to measure voltage.
The black lead should be connected to ground, the read lead connected to pin 2 along with the switch and resistor.
hi adws, i put an incorrect picture in the first post, i've edited the photo, could you take a look at it again just to make sure.
Because you have the meter connected incorrectly.
You have the meter connected to read current and set to measure voltage.
The black lead should be connected to ground the red lead connected to pin 2 along with the switch and resistor. The other side of the switch should be connected to 5V (the way it was in the first photo).
Draw the picture without the meter, the connect the probes. There is no reason to change any of the lines of the picture without the meter, in order to connect a meter to measure voltage.
adwsystems:
Because you have the meter connected incorrectly.You have the meter connected to read current and set to measure voltage.
The black lead should be connected to ground the red lead connected to pin 2 along with the switch and resistor. The other side of the switch should be connected to 5V (the way it was in the first photo).
Under the pretext of the second picture. I intended to measure the voltage.
You are right in that when I switched to Current mode, the switch now triggers.
What is the meter doing in voltage mode to cause the high state to not trigger ?
Why does the high state trigger work while the meter is in current mode ?
When electronics is boiled down to the basics, there is no way to measure current. All current measurements are actually voltage measurements over a small very accurate resistor.
In voltage mode, the meter is in parallel to the circuit and must be a super high resistance or risk shorting the power supply.
In current mode, the meter is in series (as you have drawn it) and must be a low resistance to minimize the effect on the circuit.
Please stop and redraw the picture correctly to measure voltage, then connect the meter in the correct method before you damage the meter, the circuit, or yourself.
adwsystems:
When electronics is boiled down to the basics, there is no way to measure current. All current measurements are actually voltage measurements over a small very accurate resistor.In voltage mode, the meter is in parallel to the circuit and must be a super high resistance or risk shorting the power supply.
In current mode, the meter is in series (as you have drawn it) and must be a low resistance to minimize the effect on the circuit.
Please stop and redraw the picture correctly to measure voltage, then connect the meter in the correct method before you damage the meter, the circuit, or yourself.
Like this ?
Closer. The setup is now safe, but one of the connections is still incorrect.
I will assume the red lead is connected to pin 2, the black lead should be on ground.
There should be not connection of the meter to 5V unless you are trying to measure the power supply voltage. Everything is always referenced to ground. Very, very rarely is there a need to reference to something that is not ground. This is not one of those cases.
So voltage should always be measured with all the wires connected ?
Only current measurements need to break the circuit and insert the meter ?
BigKoy:
So voltage should always be measured with all the wires connected ?Only current measurements need to break the circuit and insert the meter ?
Correct.
adwsystems:
When electronics is boiled down to the basics, there is no way to measure current. All current measurements are actually voltage measurements over a small very accurate resistor.
Not true.
Hall effect current sensors measure the magnetic field due to the current.
Analog meters are also magnetic in operation also.
So no, there are several ways to measure a current that don't require either a voltage measurement
or a resistor.
MarkT:
Not true.Hall effect current sensors measure the magnetic field due to the current.
Analog meters are also magnetic in operation also.
So no, there are several ways to measure a current that don't require either a voltage measurement
or a resistor.
Not require a resistor, yes. Read directly as current, no. Both of those methods convert the signal into a voltage.
My analog meters all have sense resistors or act as a sense resistor. I know, I have burned up and replaced all of them at least once.
adwsystems:
Not require a resistor, yes. Read directly as current, no. Both of those methods convert the signal into a voltage.My analog meters all have sense resistors or act as a sense resistor. I know, I have burned up and replaced all of them at least once.
An analog meter converts a magnetic force into an angle... You can add a resistor to make a voltmeter, but
the meter responds to current.
Though its true a hall sensor does immediately convert magnetic field to voltage, but that's not a voltage
in the circuit being measured...
adwsystems:
Correct.
Thanks for the help adw..
MarkT:
An analog meter converts a magnetic force into an angle... You can add a resistor to make a voltmeter, but
the meter responds to current.Though its true a hall sensor does immediately convert magnetic field to voltage, but that's not a voltage
in the circuit being measured...
It is still voltage being measured in order to display current.
Back on topic...
With a multimeter... You just need to remember... You measure voltage ACROSS something, so put the probes ACROSS a component - parallel connected (i.e. put a probe either side of the component / part of the circuit you want to see)
You measure current THROUGH something, so put your meter in the circuit - series connected (i.e. break the circuit and stick the meter in line with it).
Getting this wrong CAN cause damage - ensure your meter is set to the correct mode every time!
fall-apart-dave:
Back on topic...With a multimeter... You just need to remember... You measure voltage ACROSS something, so put the probes ACROSS a component - parallel connected (i.e. put a probe either side of the component / part of the circuit you want to see)
You measure current THROUGH something, so put your meter in the circuit - series connected (i.e. break the circuit and stick the meter in line with it).
Getting this wrong CAN cause damage - ensure your meter is set to the correct mode every time!
Thanks for the succinct f-a-d
Don't worry about my meters, I got them all free from harbor freight. and have plenty more stocked.
You don't have to measure relative to ground... If you have 12V and 5V (with a common ground) you can connect the black -lead to 5V, and the red +lead to 15V and the meter will read 7V. Or, you can reverse the leads and you'll read -7V.
But, the Arduino's ADC ONLY reads relative to it's ground and the Arduino can be damaged by negative voltages (or voltages greater than +5V).
Off topic, but...
It is still voltage being measured in order to display current.
That might be true with a "modern analog" multimeter, but the original analog meters* had no active electronics. The electro-magnetic meter movement was deflected by CURRENT through the coil, and resistors were switched-in for the various current & voltage measurements. Series resistance for voltage measurement and parallel resistance for current measurement.
If you had the specs for the internal meter movement you'd see a full-range current spec and a resistance spec. Of course, you could calculate the voltage but the meter movement is deflected by current and that's how it's specified.
In the voltage-range, current was "converted" to a give a voltage measurement... The opposite of how a DVM works.
These old analog meters would measure voltage & current without a battery. The battery was only used for resistance measurements.
Wonder, if you gave the "modern" man a Simpson 260 (like I used for 30 years), how long it would take for the magic smoke to pour? 
