Data Sheet
-119-
297. Floating Inputs
Replace the switch (62) with the press switch (61) in project #287.
Press and hold the press switch (61) and you will hear sounds of a
police siren from the speaker (93). Also, you will see the motor (95) is
spinning at the same time. A oating input is one that is not connected
to anything. While this circuit has not connected the T1, T2, I/O1 and
I/O2 inputs to anything external to the 3-in-1 (11), internally it’s possible
the 3-in-1 has tied these inputs to ground or 4.5V through a resistor, so
they are not actually oating inputs.
298. Benets of High Input Impedance
Connect points C and D with a 4-wire (4) in project #297. Press and
hold the press switch (61) and you will hear gun shots and the motor
(95) will spin at the same time. As discussed in project #293, T2 is a
high impedance input. The benet of high impedance inputs is that they
consume less power due to the small current required to activate them.
299. Output Impedance
Connect points A and B with a 4-wire (4) in project #297. Press and
hold the press switch (61) and you will hear a re siren and the motor
(95) will spin at the same time. The speaker outputs SP1 and SP2 have
output impedance. Output impedance is a measure of the change in
output voltage to the change in load current.
300. Thevinin’s Theorem
Connect points E and F with a 4-wire (4) in project #297. Press and
hold the press switch (61) and the sounds of space battle will turn
on and the motor (95) will spin at the same time. Thevinin’s Theorem
states that any linear electrical network consisting entirely of voltage
and current sources and resistances can be replaced by an equivalent
voltage source and an equivalent resistance. Project #53 showed an
example of how an equivalent resistance can be calculated.
301. Admittance
Connect points G and H with a 4-wire (4) in project #297. Press and
hold the press switch (61) and you will hear music and the motor (95)
will spin at the same time. Admittance is the reciprocal of impedance,
that is admittance = 1/impedance. So admittance is a measure of how
easily a circuit will let current ow.
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