cameronasmith:
is it that all multimeters are not 100% accurate?
Yes.
Also, no voltage regulator is 100% accurate.
cameronasmith:
2. Sometimes the voltage fluctuates. Do you think that's me touching wires by mistake or I have too small capacitors?
How much?
cameronasmith:
2. Sometimes the voltage 3. Even though IC state that they need 5 volts is the some leeway in that. For example 4.9 or 5.1 volts is okay?
Yes. You should aim for 5.0V but most ICs will work with up to 10% difference (see datasheet for the IC for exact numbers).
Although I am not sure about the quality of your meter, there is usually a small ripple on the VCC line. less than 5mv difference is pretty good actually. You meter samples a couple of times per second. The ripple is on top of the basic Vcc voltage. One sample might be at the top of a ripple, the other at the bottom. looks good to me.
I usually use 1 - 5uF caps on the regulators output to improve regulation. Also I add a 100nF ceramic cap at both the input and output of the regulator so supress any noise.
I guess when I read about electronics I always thought everything was perfect. But, when you start applying what you have learned you start to see that nothing is perfect. It just runs within margins of tolerance.
Nothing is perfect. Build a house or shed, 1/16 inch is close enough. Build a cabinet, 1/128 inch is fantastic.
When designing a circuit, it is best if your circuit can work correctly with 5% resistors, 20% capacitors, and anywhere from 10% or worse variation in Vcc. It can get quite expensive to require better components. Some parts will require better precision, or at least calibration.
polymorph:
When designing a circuit, it is best if your circuit can work correctly with 5% resistors, 20% capacitors, and anywhere from 10% or worse variation in Vcc. It can get quite expensive to require better components. Some parts will require better precision, or at least calibration.
Most 3.5 digit meters are range 1.999, 19.99 and 199.9 volts. (the "1" is what is called the half digit) So if you are measuring 5 volts you are probably using the 20 volt range.
Calibration tolerance is usually (almost always) referenced to full scale so the 0.5% error is actually referenced to 20 volts which equates to +- 0.1 volts
Hence your 5 volts could actually display as anywhere between 4.900 and 5.100 volts
Then there is the +- 1 digit tolerance of the ADC that drives the display so we now get anywhere from 4.899 to 5.101
The 1 digit flicker you see is probably the 1 digit tolerance of the ADC
So with the best will in the world, measurement is at best a "near enough" science.
If your meter is reading anywhere in the range 4.899 to 5.101 you can be reasonably confident that the 7805 output is to spec.
This is why if you are trying to use the analogRead() command to measure anything with any sort of accuracy, it is better to use the internal reference or an external reference, rather than the default which uses Vcc.
