Questions about LEDs and meters

[smiles]

Hi ! Could you tell me why the LED is bright when I put two probe tests of analog meter at its cathode and anode, but it isn't bright when using digital meter at the same way ?
And with two similar LED, why this one is brighter than another ?
... and why analog calculation is more complex than digital calculation ?
Thanks so much !!!

 

[IanP]

Re: Led and meters

Meters use different test currents ..
In your case, if the analog meter's test current is, say, 1mA, and the digital meters's less than that, the LED connected to the digital meter will be brighter ..

Regards,
IanP

 

[hbaocr]

Led and meters

hi,smiles
example
that reply on structure of Voltmetter which you use. infact that VOM measure voltage drop on resistor so In some type of vom can generate current I(ma) and get back a voltage on resistor
V=R*I . That a reason when you choose Resistor measure mode,and choose lowest scale the current I(ma) can make led bright. It reply on the impedance input of VOM

your LED is bright , because there is a voltage betwen 2 probe about and it generate current through led and make it bright. You can use this feature of VOM to test led.


and for the second question
Arcdoind to me, the digital system is easy to design , and easy to connect many modules together without computing moe complex, You can only notice the impedace I/0 , the protocol of each modules, the level logic voltage, It it low nosie then analog

 

[rikie_rizza]

Led and meters

Two LED are brighter then the other because of several reasons, one is the not uniform of the current limiting resistor. other is, when you bought LED at a somponent store, they usualy came from several manufacturer but mixed together. This could cause differences between LEDs.

And about the digital question: think about this... if you have numbers between 1 and 0, how many can you have? If you are an analog system you could have unlimited number like 0.1 or 0.000001 or 0.0009009000001 or else. But if you are a digital system, than you only those two... 1 and 0 and nothing in between.

That means you only have two state... high, low; cold, hot not warm or a bit cold. because it is that simple, digital system is easier to manipulate than analog system.