Goto page Previous 1, 2, 3 Next
chuckcar
Guest
Mon Jul 13, 2009 4:34 am
John Fields <jfields_at_austininstruments.com> wrote in
news:6r1k551jc5uasev62m1v0vl43vo2b2t6hd_at_4ax.com:
Quote:
On Sat, 11 Jul 2009 21:50:55 +0000 (UTC), chuckcar <chuck_at_nil.car
wrote:
"ian field" <gangprobing.alien_at_ntlworld.com> wrote in
news:VZ56m.172$Ae3.44_at_newsfe01.ams2:
"chuckcar" <chuck_at_nil.car> wrote in message
news:Xns9C459893424AFchucknilcar_at_127.0.0.1...
"hhgggff" <ohu_at_klg.con> wrote in
news:Do16m.54775$OO7.27875_at_text.news.virginmedia.com:
My friends dad is building a Tardis for his grandson.
We have rigged up the blue flashing light using a 12 volt car
battery, we now need to sort out the sounds.
I was thinking of using an old cars cassette tape, but I have an old
9 volt portable cassette handy.
Will it burn down the TARDIS if I use that instead ?
The tape motor will run at the wrong speed for one. What you need is
a voltage regulator. A 7809 should do the trick. The 7800 series
convert DC voltages. Granted a transformer does it, but these handle
*much* wider voltage inputs and are tiny in comparison. A 7812 hooked
to the +12v connection with the other connection hooked to a 200
microfarad capacitor should give you a rock solid +9v out. You'll
need a piece of breadboard about 1" square to mount these on.
You should read up on a subject you know little about before giving
advice to others.
Considering the fact that my post is *far* more detailed than yours,
you're hardly a person to make such a judgement = along with your errors
detaied below.
---
The fact that your post was more "detailed" than Ian's doesn't mean that
his was wrong.
---
Even in older cassette recorders the motors had centrifugal speed
governors and modern ones have an IC speed controller (otherwise
they'd run slower and slower as the battery was used).
And none of this would burn out with 1 1/3 times the voltage input?
dubious.
---
Just conjecture without knowing more about the cassette recorder.
---
Your mention of transformers is misleading, without a "chopper"
circuit to convert DC into AC a transformer will burn out.
He's *using* a DC power source - a car battery. So a rectifier circuit
or an analogue is completely unncessary
---
But, since his application runs on DC, your reference to a transformer
was misleading since a transformer takes an AC input and supplies an AC
output which must then be rectified, filtered, and possibly regulated
before it can be used by the DC input device.
If, by "transformer", you meant an AC to DC converter, then your
terminology was wrong.
---
The OP is best advised to ask people who are equipped to give accurate
advice, such as the folk on News:sci.electronics.basics .
One *minor* correction of my post however - that *should* have been a
7809 not a 7812. This I picked up immediately when I read your reply. A
pretty basic error you didn't even notice. a 7812 converts *to* 12v
whereas a 7809 converts to 5v. Hence their names.
---
???
A 7809 converts to 9V, not 5V.
Message-ID: <Xns9C45EFC12936Cchucknilcar_at_127.0.0.1
Quote:
In addition, not knowing the current requirements of the recorder, your
comment to build it on one square inch of breadboard (perfboard?) may
well be inconsistent with the heat-sinking required for the regulator.
And why the 200µF capacitor?
Why not 10?
Too small to absorb the variations
Quote:
Why not 1000?
Way too big for the voltage.
--
(setq (chuck nil) car(chuck) )
John Fields
Guest
Mon Jul 13, 2009 1:06 pm
On Mon, 13 Jul 2009 02:34:52 +0000 (UTC), chuckcar <chuck_at_nil.car>
wrote:
Quote:
John Fields <jfields_at_austininstruments.com> wrote in
news:6r1k551jc5uasev62m1v0vl43vo2b2t6hd_at_4ax.com:
On Sat, 11 Jul 2009 21:50:55 +0000 (UTC), chuckcar <chuck_at_nil.car
wrote:
"ian field" <gangprobing.alien_at_ntlworld.com> wrote in
news:VZ56m.172$Ae3.44_at_newsfe01.ams2:
"chuckcar" <chuck_at_nil.car> wrote in message
news:Xns9C459893424AFchucknilcar_at_127.0.0.1...
"hhgggff" <ohu_at_klg.con> wrote in
news:Do16m.54775$OO7.27875_at_text.news.virginmedia.com:
My friends dad is building a Tardis for his grandson.
We have rigged up the blue flashing light using a 12 volt car
battery, we now need to sort out the sounds.
I was thinking of using an old cars cassette tape, but I have an old
9 volt portable cassette handy.
Will it burn down the TARDIS if I use that instead ?
The tape motor will run at the wrong speed for one. What you need is
a voltage regulator. A 7809 should do the trick. The 7800 series
convert DC voltages. Granted a transformer does it, but these handle
*much* wider voltage inputs and are tiny in comparison. A 7812 hooked
to the +12v connection with the other connection hooked to a 200
microfarad capacitor should give you a rock solid +9v out. You'll
need a piece of breadboard about 1" square to mount these on.
You should read up on a subject you know little about before giving
advice to others.
Considering the fact that my post is *far* more detailed than yours,
you're hardly a person to make such a judgement = along with your errors
detaied below.
---
The fact that your post was more "detailed" than Ian's doesn't mean that
his was wrong.
---
Even in older cassette recorders the motors had centrifugal speed
governors and modern ones have an IC speed controller (otherwise
they'd run slower and slower as the battery was used).
And none of this would burn out with 1 1/3 times the voltage input?
dubious.
---
Just conjecture without knowing more about the cassette recorder.
---
Your mention of transformers is misleading, without a "chopper"
circuit to convert DC into AC a transformer will burn out.
He's *using* a DC power source - a car battery. So a rectifier circuit
or an analogue is completely unncessary
---
But, since his application runs on DC, your reference to a transformer
was misleading since a transformer takes an AC input and supplies an AC
output which must then be rectified, filtered, and possibly regulated
before it can be used by the DC input device.
If, by "transformer", you meant an AC to DC converter, then your
terminology was wrong.
---
The OP is best advised to ask people who are equipped to give accurate
advice, such as the folk on News:sci.electronics.basics .
One *minor* correction of my post however - that *should* have been a
7809 not a 7812. This I picked up immediately when I read your reply. A
pretty basic error you didn't even notice. a 7812 converts *to* 12v
whereas a 7809 converts to 5v. Hence their names.
---
???
A 7809 converts to 9V, not 5V.
Message-ID: <Xns9C45EFC12936Cchucknilcar_at_127.0.0.1
In addition, not knowing the current requirements of the recorder, your
comment to build it on one square inch of breadboard (perfboard?) may
well be inconsistent with the heat-sinking required for the regulator.
And why the 200µF capacitor?
Why not 10?
Too small to absorb the variations
---
What variations?
---
Quote:
Why not 1000?
Way too big for the voltage.
---
Why?
JF
Zootal
Guest
Tue Jul 14, 2009 3:58 am
"John Fields" <jfields_at_austininstruments.com> wrote in message
news:f8cm55htprevsh4nnnjhao8jlb3a9bu3k5_at_4ax.com...
Quote:
On Mon, 13 Jul 2009 02:34:52 +0000 (UTC), chuckcar <chuck_at_nil.car
wrote:
John Fields <jfields_at_austininstruments.com> wrote in
news:6r1k551jc5uasev62m1v0vl43vo2b2t6hd_at_4ax.com:
On Sat, 11 Jul 2009 21:50:55 +0000 (UTC), chuckcar <chuck_at_nil.car
wrote:
"ian field" <gangprobing.alien_at_ntlworld.com> wrote in
news:VZ56m.172$Ae3.44_at_newsfe01.ams2:
"chuckcar" <chuck_at_nil.car> wrote in message
news:Xns9C459893424AFchucknilcar_at_127.0.0.1...
"hhgggff" <ohu_at_klg.con> wrote in
news:Do16m.54775$OO7.27875_at_text.news.virginmedia.com:
My friends dad is building a Tardis for his grandson.
We have rigged up the blue flashing light using a 12 volt car
battery, we now need to sort out the sounds.
I was thinking of using an old cars cassette tape, but I have an old
9 volt portable cassette handy.
Will it burn down the TARDIS if I use that instead ?
The tape motor will run at the wrong speed for one. What you need is
a voltage regulator. A 7809 should do the trick. The 7800 series
convert DC voltages. Granted a transformer does it, but these handle
*much* wider voltage inputs and are tiny in comparison. A 7812 hooked
to the +12v connection with the other connection hooked to a 200
microfarad capacitor should give you a rock solid +9v out. You'll
need a piece of breadboard about 1" square to mount these on.
You should read up on a subject you know little about before giving
advice to others.
Considering the fact that my post is *far* more detailed than yours,
you're hardly a person to make such a judgement = along with your errors
detaied below.
---
The fact that your post was more "detailed" than Ian's doesn't mean that
his was wrong.
---
Even in older cassette recorders the motors had centrifugal speed
governors and modern ones have an IC speed controller (otherwise
they'd run slower and slower as the battery was used).
And none of this would burn out with 1 1/3 times the voltage input?
dubious.
---
Just conjecture without knowing more about the cassette recorder.
---
Your mention of transformers is misleading, without a "chopper"
circuit to convert DC into AC a transformer will burn out.
He's *using* a DC power source - a car battery. So a rectifier circuit
or an analogue is completely unncessary
---
But, since his application runs on DC, your reference to a transformer
was misleading since a transformer takes an AC input and supplies an AC
output which must then be rectified, filtered, and possibly regulated
before it can be used by the DC input device.
If, by "transformer", you meant an AC to DC converter, then your
terminology was wrong.
---
The OP is best advised to ask people who are equipped to give accurate
advice, such as the folk on News:sci.electronics.basics .
One *minor* correction of my post however - that *should* have been a
7809 not a 7812. This I picked up immediately when I read your reply. A
pretty basic error you didn't even notice. a 7812 converts *to* 12v
whereas a 7809 converts to 5v. Hence their names.
---
???
A 7809 converts to 9V, not 5V.
Message-ID: <Xns9C45EFC12936Cchucknilcar_at_127.0.0.1
In addition, not knowing the current requirements of the recorder, your
comment to build it on one square inch of breadboard (perfboard?) may
well be inconsistent with the heat-sinking required for the regulator.
And why the 200µF capacitor?
Why not 10?
Too small to absorb the variations
---
What variations?
---
Why not 1000?
Way too big for the voltage.
---
Why?
A 1000µF cap on the output of a 78xx or 79xx regulator will work just fine.
It's just not necessary, but I don't think the power up surge of charging
the cap would hurt the regulator any, and once it's charged the circuit
should work fine.
If you are making a half million gizmos, you would want to use the smallest
cap you can get away with. Use a cap that cost a dollar less, and you just
saved a half million dollars.
hhgggff
Guest
Fri Jul 17, 2009 2:24 pm
Quote:
I was thinking of using an old cars cassette tape, but I have an old 9
volt
portable cassette handy.
Well, In the end I just plugged it in and it works,correct speed.
tafankuverymuch
ian field
Guest
Fri Jul 17, 2009 3:57 pm
"hhgggff" <ohu_at_klg.con> wrote in message
news:cQ%7m.57494$OO7.26422_at_text.news.virginmedia.com...
Quote:
I was thinking of using an old cars cassette tape, but I have an old 9
volt
portable cassette handy.
Well, In the end I just plugged it in and it works,correct speed.
tafankuverymuch
If you're running a 9V cassette player from a car battery, don't run it at
full volume - the audio output might be the weak link.
Roger Dewhurst
Guest
Thu Jul 23, 2009 11:07 pm
Quote:
You can get simple to use regulator chips that drop the voltage down, you
only need a couple of components to make a working voltage regulator. Ask on
News:sci.electronics.basic - the folk on there are usually very helpful and
should explain all you need.
Why not just drop the voltage through a few diodes? Very simple. Very
cheap.
R
rf
Guest
Fri Jul 24, 2009 9:47 am
Roger Dewhurst wrote:
Quote:
You can get simple to use regulator chips that drop the voltage
down, you only need a couple of components to make a working voltage
regulator. Ask on News:sci.electronics.basic - the folk on there are
usually very helpful and should explain all you need.
Why not just drop the voltage through a few diodes? Very simple. Very
cheap.
A *few* diodes at a couple of ten cents per each. A single 7809 for less
that a $.
Ian Jackson
Guest
Wed Jul 29, 2009 9:40 pm
In message <Bqfam.7029$ze1.6612_at_news-server.bigpond.net.au>, rf
<rf_at_z.invalid> writes
Quote:
Roger Dewhurst wrote:
You can get simple to use regulator chips that drop the voltage
down, you only need a couple of components to make a working voltage
regulator. Ask on News:sci.electronics.basic - the folk on there are
usually very helpful and should explain all you need.
Why not just drop the voltage through a few diodes? Very simple. Very
cheap.
A *few* diodes at a couple of ten cents per each. A single 7809 for less
that a $.
More like "a *few* diodes at a couple of cents per each".
3V to drop = 5 diodes @ 0.6V per diode. No other circuitry required.
More than good enough for the job.
--
Ian
ian field
Guest
Wed Jul 29, 2009 9:58 pm
"Ian Jackson" <ianREMOVETHISjackson_at_g3ohx.demon.co.uk> wrote in message
news:RK8$DzIdHMcKFwRq_at_g3ohx.demon.co.uk...
Quote:
In message <Bqfam.7029$ze1.6612_at_news-server.bigpond.net.au>, rf
rf_at_z.invalid> writes
Roger Dewhurst wrote:
You can get simple to use regulator chips that drop the voltage
down, you only need a couple of components to make a working voltage
regulator. Ask on News:sci.electronics.basic - the folk on there are
usually very helpful and should explain all you need.
Why not just drop the voltage through a few diodes? Very simple. Very
cheap.
A *few* diodes at a couple of ten cents per each. A single 7809 for less
that a $.
More like "a *few* diodes at a couple of cents per each".
3V to drop = 5 diodes @ 0.6V per diode. No other circuitry required. More
than good enough for the job.
--
Ian
The forward conduction knee curve on diodes isn't *that* sharp, depending on
current draw and rating of the diode the drop can be as low as 0.55V and as
high as 1.1V.
rf
Guest
Wed Jul 29, 2009 11:48 pm
"Ian Jackson" <ianREMOVETHISjackson_at_g3ohx.demon.co.uk> wrote in message
news:RK8$DzIdHMcKFwRq_at_g3ohx.demon.co.uk...
Quote:
In message <Bqfam.7029$ze1.6612_at_news-server.bigpond.net.au>, rf
rf_at_z.invalid> writes
Roger Dewhurst wrote:
You can get simple to use regulator chips that drop the voltage
down, you only need a couple of components to make a working voltage
regulator. Ask on News:sci.electronics.basic - the folk on there are
usually very helpful and should explain all you need.
Why not just drop the voltage through a few diodes? Very simple. Very
cheap.
A *few* diodes at a couple of ten cents per each. A single 7809 for less
that a $.
More like "a *few* diodes at a couple of cents per each".
3V to drop = 5 diodes @ 0.6V per diode. No other circuitry required. More
than good enough for the job.
Exactly one 7809 for less than a buck. No other circutry required. Perfect
regulation.
Ian Jackson
Guest
Thu Jul 30, 2009 7:19 am
In message <AC3cm.163781$bA.81816_at_newsfe16.ams2>, ian field
<gangprobing.alien_at_ntlworld.com> writes
Quote:
"Ian Jackson" <ianREMOVETHISjackson_at_g3ohx.demon.co.uk> wrote in message
news:RK8$DzIdHMcKFwRq_at_g3ohx.demon.co.uk...
In message <Bqfam.7029$ze1.6612_at_news-server.bigpond.net.au>, rf
rf_at_z.invalid> writes
Roger Dewhurst wrote:
You can get simple to use regulator chips that drop the voltage
down, you only need a couple of components to make a working voltage
regulator. Ask on News:sci.electronics.basic - the folk on there are
usually very helpful and should explain all you need.
Why not just drop the voltage through a few diodes? Very simple. Very
cheap.
A *few* diodes at a couple of ten cents per each. A single 7809 for less
that a $.
More like "a *few* diodes at a couple of cents per each".
3V to drop = 5 diodes @ 0.6V per diode. No other circuitry required. More
than good enough for the job.
--
Ian
The forward conduction knee curve on diodes isn't *that* sharp, depending on
current draw and rating of the diode the drop can be as low as 0.55V and as
high as 1.1V.
For most 'normal' Si diodes, that isn't really the case. The actual
voltage drop does, of course, increase with current, but at 'sensible'
currents, you can reckon on around 0.65V per diode. How much current is
the Tardis toy going to take? 1A max? 4 or 5 1N4000-series diodes should
work fine in this application. I've used this non-elegant 'KISS'
technique on several occasions, and haven't found any problems.
--
Ian
ian field
Guest
Thu Jul 30, 2009 1:52 pm
"Ian Jackson" <ianREMOVETHISjackson_at_g3ohx.demon.co.uk> wrote in message
news:oQqRlSBFmUcKFw3i_at_g3ohx.demon.co.uk...
Quote:
In message <AC3cm.163781$bA.81816_at_newsfe16.ams2>, ian field
gangprobing.alien_at_ntlworld.com> writes
"Ian Jackson" <ianREMOVETHISjackson_at_g3ohx.demon.co.uk> wrote in message
news:RK8$DzIdHMcKFwRq_at_g3ohx.demon.co.uk...
In message <Bqfam.7029$ze1.6612_at_news-server.bigpond.net.au>, rf
rf_at_z.invalid> writes
Roger Dewhurst wrote:
You can get simple to use regulator chips that drop the voltage
down, you only need a couple of components to make a working voltage
regulator. Ask on News:sci.electronics.basic - the folk on there are
usually very helpful and should explain all you need.
Why not just drop the voltage through a few diodes? Very simple. Very
cheap.
A *few* diodes at a couple of ten cents per each. A single 7809 for less
that a $.
More like "a *few* diodes at a couple of cents per each".
3V to drop = 5 diodes @ 0.6V per diode. No other circuitry required.
More
than good enough for the job.
--
Ian
The forward conduction knee curve on diodes isn't *that* sharp, depending
on
current draw and rating of the diode the drop can be as low as 0.55V and
as
high as 1.1V.
For most 'normal' Si diodes, that isn't really the case. The actual
voltage drop does, of course, increase with current, but at 'sensible'
currents, you can reckon on around 0.65V per diode. How much current is
the Tardis toy going to take? 1A max? 4 or 5 1N4000-series diodes should
work fine in this application. I've used this non-elegant 'KISS' technique
on several occasions, and haven't found any problems.
--
Ian
A potential danger with a cassette recorder is the difference in current
draw between motor on and motor off. In the condition of low current draw
(and low diode drop) supply decoupling electrolytic capacitors can charge to
a higher voltage which is then dumped into the circuit when switched to
play.
ian field
Guest
Thu Jul 30, 2009 2:03 pm
"rf" <rf_at_z.invalid> wrote in message
news:5d5cm.8142$ze1.7151_at_news-server.bigpond.net.au...
Quote:
"Ian Jackson" <ianREMOVETHISjackson_at_g3ohx.demon.co.uk> wrote in message
news:RK8$DzIdHMcKFwRq_at_g3ohx.demon.co.uk...
In message <Bqfam.7029$ze1.6612_at_news-server.bigpond.net.au>, rf
rf_at_z.invalid> writes
Roger Dewhurst wrote:
You can get simple to use regulator chips that drop the voltage
down, you only need a couple of components to make a working voltage
regulator. Ask on News:sci.electronics.basic - the folk on there are
usually very helpful and should explain all you need.
Why not just drop the voltage through a few diodes? Very simple. Very
cheap.
A *few* diodes at a couple of ten cents per each. A single 7809 for less
that a $.
More like "a *few* diodes at a couple of cents per each".
3V to drop = 5 diodes @ 0.6V per diode. No other circuitry required. More
than good enough for the job.
Exactly one 7809 for less than a buck. No other circutry required. Perfect
regulation.
Not *quite* no extra circuitry, they require decoupling capacitors on the
input and output otherwise they can break into oscillation. If a 3-terminal
regulator feeds a circuit with a large supply decoupling electrolytic
(possibility of stored charge feeding backwards through the regulator when
the input voltage is switched off) its advisable to strap a diode between
the input and output terminals, otherwise the regulator can be damaged - not
conducting in the normal condition of input voltage being higher than the
output but conducts if the output tries to go higher than the input.
Ian Jackson
Guest
Thu Jul 30, 2009 3:04 pm
In message <HAhcm.73167$561.68469_at_newsfe28.ams2>, ian field
<gangprobing.alien_at_ntlworld.com> writes
Quote:
"Ian Jackson" <ianREMOVETHISjackson_at_g3ohx.demon.co.uk> wrote in message
news:oQqRlSBFmUcKFw3i_at_g3ohx.demon.co.uk...
In message <AC3cm.163781$bA.81816_at_newsfe16.ams2>, ian field
gangprobing.alien_at_ntlworld.com> writes
"Ian Jackson" <ianREMOVETHISjackson_at_g3ohx.demon.co.uk> wrote in message
news:RK8$DzIdHMcKFwRq_at_g3ohx.demon.co.uk...
In message <Bqfam.7029$ze1.6612_at_news-server.bigpond.net.au>, rf
rf_at_z.invalid> writes
Roger Dewhurst wrote:
You can get simple to use regulator chips that drop the voltage
down, you only need a couple of components to make a working voltage
regulator. Ask on News:sci.electronics.basic - the folk on there are
usually very helpful and should explain all you need.
Why not just drop the voltage through a few diodes? Very simple. Very
cheap.
A *few* diodes at a couple of ten cents per each. A single 7809 for less
that a $.
More like "a *few* diodes at a couple of cents per each".
3V to drop = 5 diodes @ 0.6V per diode. No other circuitry required.
More
than good enough for the job.
--
Ian
The forward conduction knee curve on diodes isn't *that* sharp, depending
on
current draw and rating of the diode the drop can be as low as 0.55V and
as
high as 1.1V.
For most 'normal' Si diodes, that isn't really the case. The actual
voltage drop does, of course, increase with current, but at 'sensible'
currents, you can reckon on around 0.65V per diode. How much current is
the Tardis toy going to take? 1A max? 4 or 5 1N4000-series diodes should
work fine in this application. I've used this non-elegant 'KISS' technique
on several occasions, and haven't found any problems.
--
Ian
A potential danger with a cassette recorder is the difference in current
draw between motor on and motor off. In the condition of low current draw
(and low diode drop) supply decoupling electrolytic capacitors can charge to
a higher voltage which is then dumped into the circuit when switched to
play.
True, true. But I reckon that a momentary short burst of a
rapidly-decaying additional 3V won't hurt too much.
--
Ian
Zootal
Guest
Thu Jul 30, 2009 4:05 pm
"Ian Jackson" <ianREMOVETHISjackson_at_g3ohx.demon.co.uk> wrote in message
news:GvAqKUAuZbcKFwgH_at_g3ohx.demon.co.uk...
Quote:
In message <HAhcm.73167$561.68469_at_newsfe28.ams2>, ian field
gangprobing.alien_at_ntlworld.com> writes
"Ian Jackson" <ianREMOVETHISjackson_at_g3ohx.demon.co.uk> wrote in message
news:oQqRlSBFmUcKFw3i_at_g3ohx.demon.co.uk...
In message <AC3cm.163781$bA.81816_at_newsfe16.ams2>, ian field
gangprobing.alien_at_ntlworld.com> writes
"Ian Jackson" <ianREMOVETHISjackson_at_g3ohx.demon.co.uk> wrote in message
news:RK8$DzIdHMcKFwRq_at_g3ohx.demon.co.uk...
In message <Bqfam.7029$ze1.6612_at_news-server.bigpond.net.au>, rf
rf_at_z.invalid> writes
Roger Dewhurst wrote:
You can get simple to use regulator chips that drop the voltage
down, you only need a couple of components to make a working
voltage
regulator. Ask on News:sci.electronics.basic - the folk on there
are
usually very helpful and should explain all you need.
Why not just drop the voltage through a few diodes? Very simple.
Very
cheap.
A *few* diodes at a couple of ten cents per each. A single 7809 for
less
that a $.
More like "a *few* diodes at a couple of cents per each".
3V to drop = 5 diodes @ 0.6V per diode. No other circuitry required.
More
than good enough for the job.
--
Ian
The forward conduction knee curve on diodes isn't *that* sharp,
depending
on
current draw and rating of the diode the drop can be as low as 0.55V and
as
high as 1.1V.
For most 'normal' Si diodes, that isn't really the case. The actual
voltage drop does, of course, increase with current, but at 'sensible'
currents, you can reckon on around 0.65V per diode. How much current is
the Tardis toy going to take? 1A max? 4 or 5 1N4000-series diodes should
work fine in this application. I've used this non-elegant 'KISS'
technique
on several occasions, and haven't found any problems.
--
Ian
A potential danger with a cassette recorder is the difference in current
draw between motor on and motor off. In the condition of low current draw
(and low diode drop) supply decoupling electrolytic capacitors can charge
to
a higher voltage which is then dumped into the circuit when switched to
play.
True, true. But I reckon that a momentary short burst of a
rapidly-decaying additional 3V won't hurt too much.
--
Ian
It won't even be noticeable. The capacitors won't charge up that high to
start with, and they don't "dump" into the circuit, they just quickly
discharge down to the lower voltage that is present at the output of the
last diode - how fast this happens depends on the size of the caps and the
load. I wouldn't even call it a surge. A resistor from the last diode to
ground will prevent them from charging more then a few tenths of a volt and
is a good idea. And the capacitor doesn't need to be that big.
I would *not* use 1n400x diodes. ~1 amp will make them hot and susceptible
to failure. Use 2 or 3 amp diodes, they are cheap and readily available.
They are bigger and will run cooler and won't fail as easily. Or use two
strings of 1n400x in series, that is good enough for an app like this.
So - 12v -> diode -> diode -> diode -> diode -> ~9.2v Output
From the output run a 470 ohm half watt resistor through a standard 1/4" LED
to ground (I like the LED so you can see when the circuit is on). In
parallel to this connect a capacitor, say 100uF. Presto, ~9.2V, adequately
regulated, and minimal voltage increase when the load is off.
Goto page Previous 1, 2, 3 Next
