Guest
In this circuit:
http://kitsrus.com/projects/k48.pdf
Why is the other end of RV1 grounded?
Thanks,
Michael
http://kitsrus.com/projects/k48.pdf
Why is the other end of RV1 grounded?
Thanks,
Michael
Guest
On Nov 14, 10:24 am, mrdarr...@gmail.com wrote:
Never mind... I think it has something to do with the input
impedance...
Michael
Never mind... I think it has something to do with the input
impedance...
Michael
J
John Fields
Guest
On Fri, 14 Nov 2008 10:32:50 -0800 (PST), mrdarrett@gmail.com wrote:
Only incidentally.
Think about it like this:
At the top of the pot the input signal will be at its maximum amplitude
since that's connected to the output of the signal source, and at the
bottom of the pot it'll be at 0 volts, since that's ground. Anywhere in
between it'll be somewhere between max and 0.
What you have with a potentiometer is what looks like two resistors in
series with the slider at their junction, like this:
VIN>---+
|
[R1]
|
+------->VOUT
|
[R2]
|
GND>---+------->GND
Since it's a 10k pot, let's assume the slider is located half-way
between the two ends, like this:
EIN>---+
|
[5k]
|
+------->VOUT
|
[5k]
|
GND>---+------->GND
Then, if we relabel the circuit for convenience:
E1
|
[R1]
|
+---E2
|
[R2]
|
GND
we can say:
E1 * R2 1V * 5kR
E2 = --------- = ---------- = 0.5V
E1 + R2 1V + 5kR
If you solve that equation for the slider being located anywhere along
the element and remember that both sides of the pot have to add up to
10k, you'll find that E2 will increase more and more as the slider gets
closer and closer to the E1 end of the pot and that E2 will decrease
more and more as the slider gets closer and closer to the GND end of the
pot.
So what is it?
It's a volume control!
JF
---
Only incidentally.
Think about it like this:
At the top of the pot the input signal will be at its maximum amplitude
since that's connected to the output of the signal source, and at the
bottom of the pot it'll be at 0 volts, since that's ground. Anywhere in
between it'll be somewhere between max and 0.
What you have with a potentiometer is what looks like two resistors in
series with the slider at their junction, like this:
VIN>---+
|
[R1]
|
+------->VOUT
|
[R2]
|
GND>---+------->GND
Since it's a 10k pot, let's assume the slider is located half-way
between the two ends, like this:
EIN>---+
|
[5k]
|
+------->VOUT
|
[5k]
|
GND>---+------->GND
Then, if we relabel the circuit for convenience:
E1
|
[R1]
|
+---E2
|
[R2]
|
GND
we can say:
E1 * R2 1V * 5kR
E2 = --------- = ---------- = 0.5V
E1 + R2 1V + 5kR
If you solve that equation for the slider being located anywhere along
the element and remember that both sides of the pot have to add up to
10k, you'll find that E2 will increase more and more as the slider gets
closer and closer to the E1 end of the pot and that E2 will decrease
more and more as the slider gets closer and closer to the GND end of the
pot.
So what is it?
It's a volume control!
JF
J
John Fields
Guest
On Fri, 14 Nov 2008 14:52:35 -0600, John Fields
<jfields@austininstruments.com> wrote:
Tsk, tsk, tsk...
E1 * R2 1V * 5kR
E2 = --------- = ---------- = 0.5V
R1 + R2 5kR + 5kR
JF
<jfields@austininstruments.com> wrote:
---
Tsk, tsk, tsk...
E1 * R2 1V * 5kR
E2 = --------- = ---------- = 0.5V
R1 + R2 5kR + 5kR
JF
P
Peter Bennett
Guest
On Fri, 14 Nov 2008 10:24:19 -0800 (PST), mrdarrett@gmail.com wrote:
RV1 was not grounded, RV1 would just be a variable series resistor,
and would have very little effect on the volume.
--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca
A volume control is a variable voltage divider. If the bottom end of
RV1 was not grounded, RV1 would just be a variable series resistor,
and would have very little effect on the volume.
--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca
Guest
On Nov 14, 1:18 pm, Peter Bennett <pete...@somewhere.invalid> wrote:
Oh...
That's all I thought it was...
Ah...
Thanks John and Peter!
Michael
Oh...
That's all I thought it was...
Ah...
Thanks John and Peter!
Michael
Z
z
Guest
On Nov 14, 1:24 pm, mrdarr...@gmail.com wrote:
input impedance idea; tacking the far end to ground stabilizes the
input impedance so that the input signal is well behaved with respect
to where you set the pot at. on the other hand, if you just had a
variable resistor in series, like with the thing ungrounded, the input
signal source seeing a wildly changing impedance both in value and in
reactivity (from mostly resistance to mostly capacitative) will very
likely change its frequency response etc, unless it's nicely designed
to ignore that kind of thing.
yeah, like everybody says, and you're on the right track with your
input impedance idea; tacking the far end to ground stabilizes the
input impedance so that the input signal is well behaved with respect
to where you set the pot at. on the other hand, if you just had a
variable resistor in series, like with the thing ungrounded, the input
signal source seeing a wildly changing impedance both in value and in
reactivity (from mostly resistance to mostly capacitative) will very
likely change its frequency response etc, unless it's nicely designed
to ignore that kind of thing.
S
sbrehler
Guest
<mrdarrett@gmail.com> wrote in message
news:a4c97e0b-4b14-41dc-b5f2-169fb85d0d7d@s9g2000prg.googlegroups.com...
the schematic. Why are some labled this way: 1K5 or 2K7
Is that 1.5K , 2.7K ohms? Makes sense, I just haven't seen that before.
Scott
news:a4c97e0b-4b14-41dc-b5f2-169fb85d0d7d@s9g2000prg.googlegroups.com...
One quick question regarding the labeling conventions of the resistors in
the schematic. Why are some labled this way: 1K5 or 2K7
Is that 1.5K , 2.7K ohms? Makes sense, I just haven't seen that before.
Scott
J
Jasen Betts
Guest
On 2008-11-15, sbrehler <sbrehler@mndspring.com> wrote:
easier to read.
Look at C5 if I scale the schematic to "125%" the '.'
almost disappears, by using a letter instead of a '.' the values are
more easily read, (they could have labeled C5 100nF, I don't know why
they didn't)
they should have used vector graphics instead of pixels for
the schematic then it would scale better - but that's a different
matter
also the font they chose has the '.' skewed to the left which is
unfortunate.
bye.
Exactly right. one reason for this is it makes printed schematics
easier to read.
Look at C5 if I scale the schematic to "125%" the '.'
almost disappears, by using a letter instead of a '.' the values are
more easily read, (they could have labeled C5 100nF, I don't know why
they didn't)
they should have used vector graphics instead of pixels for
the schematic then it would scale better - but that's a different
matter
also the font they chose has the '.' skewed to the left which is
unfortunate.
bye.
S
sbrehler
Guest
Jason,
Thanks for the clarification!
Scott
"Jasen Betts" <jasen@xnet.co.nz> wrote in message
news:gfm9ch$1jd$1@reversiblemaps.ath.cx...
Thanks for the clarification!
Scott
"Jasen Betts" <jasen@xnet.co.nz> wrote in message
news:gfm9ch$1jd$1@reversiblemaps.ath.cx...