[Prev][Next][Index][Thread]

RE: RE measuring inductance



Subject:  RE: RE measuring inductance
  Date:   Mon, 5 May 97 15:36:12 UT
  From:  "William Noble" <William_B_Noble-at-msn-dot-com>
    To:  "Tesla List" <tesla-at-pupman-dot-com>


Your comment about 2 volts is suspicious - LED's are diodes which emit
when 
forward biased - depending on the LED, there will be one or more
"standard" 
diode drops in the forward direction - most red LEDs are a single diode,
so 
0.7 volts will cause them to turn on.  I have some green LEDs here that
take 
1.4 volts (e.g. they have 2 diodes in series).  You can easily determine
what 
you have by putting some current through the LED (with a suitable
dropping 
resistor) and then measuring the voltage across the LED.
I would recommend using low power LEDs not the new super bright ones for
your 
kind of work - you could use an OP amp circuit and a meter or just a DVM
too, 
of course, but the LED is pretty simple.

[Bill]  snip 

The LED requires a bit more than 2 volts to become forward biased,
and only then will current *begin* to flow through it. I have one RF
Generator that only puts out a measley 2 volts. And it has a
disgustingly high output impedance. The LED will give decent visible
indication beginning at about 1/10th of a milliamp. The series
resonant circuit has maximum current flow through it at resonance,
but the LED will only light if the VOLTAGE across the LED exceeds the
forward bias point.

[Bill]  snip