Electrolytic capacitors & playing with 556 chip

[Adam Funk]

I wired up a 556 (two 555 timers on one chip) as follows:

Timer A:
astable circuit with equal mark & space width,
R = 267 Ί, C = 1000 ¾F (electrolytic with 25 V rating),
output: 320 Ί in series with an LED,
also tied to the reset pin on Timer B

Timer B:
same astable timing arrangement,
R = 100 k Ί, C = 10 nF (non-electrolytic),
output: piezo speaker in series with a resistor


I powered this concoction with a 9 V battery, and got more or less the
expected result: the speaker alternates between silence & a
high-pitched noise, and the LED lights up when the speaker is on. The
first few cycles of timer A are a bit irregular (it stays on for a few
seconds before first switching off), but then it evens out.

When I supply the whole circuit with 3 V (two AAAs) instead, however,
(and reduce the resistance in series with the LED accordingly), the
LED stays on all & the speaker whistles all the time.


My questions:

Is tying the output of timer A to the reset pin of timer B the most
correct way to switch B on and off with A?

One of the books of 555 circuits says that electrolytic capacitors
only work properly as capacitors above 10% of their rated voltage. Is
this why timer A doesn't work on a 3 V supply?

Even with the 9 V supply, the LED doesn't go completely off when the
speaker does --- it's just noticeably dimmer than when the speaker is
on. Why?

--
When a man tells you that he got rich through hard work, ask him
whose? --- Don Marquis

 

[Tim Wescott]

On Mon, 13 Feb 2012 20:28:58 +0000, Adam Funk wrote:

I wired up a 556 (two 555 timers on one chip) as follows:

Timer A:
astable circuit with equal mark & space width, R = 267 Ί, C = 1000 ¾F
(electrolytic with 25 V rating), output: 320 Ί in series with an LED,
also tied to the reset pin on Timer B

Timer B:
same astable timing arrangement,
R = 100 k Ί, C = 10 nF (non-electrolytic), output: piezo speaker in
series with a resistor


I powered this concoction with a 9 V battery, and got more or less the
expected result: the speaker alternates between silence & a high-pitched
noise, and the LED lights up when the speaker is on. The first few
cycles of timer A are a bit irregular (it stays on for a few seconds
before first switching off), but then it evens out.

When I supply the whole circuit with 3 V (two AAAs) instead, however,
(and reduce the resistance in series with the LED accordingly), the LED
stays on all & the speaker whistles all the time.


My questions:

Is tying the output of timer A to the reset pin of timer B the most
correct way to switch B on and off with A?

One of the books of 555 circuits says that electrolytic capacitors only
work properly as capacitors above 10% of their rated voltage. Is this
why timer A doesn't work on a 3 V supply?

Even with the 9 V supply, the LED doesn't go completely off when the
speaker does --- it's just noticeably dimmer than when the speaker is
on. Why?

R = 267 is asking for a lot of current from the chip. You may want to
try using a 2.67k resistor and a 100uF cap, or even a 26.7k and a 10uF.

Also, an astable multivibrator with a 555 uses two resistors and one cap
to set the frequency and duty cycle -- what's the other resistor value?

Have you bypassed the control inputs on both timers?

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

 

[Phil Allison]

"Adam Funk"

When I supply the whole circuit with 3 V

** Where does it say a 555 will work at 3 volts??

IIRC, the range is 5 to 15 volts.


..... Phil

 

[Michael Black]

On Tue, 14 Feb 2012, Phil Allison wrote:

"Adam Funk"


When I supply the whole circuit with 3 V


** Where does it say a 555 will work at 3 volts??

IIRC, the range is 5 to 15 volts.

Yes, and that was the obvious thing I noticed about the post.

I've never actually tried the 555 at a lower voltage.

Perhaps the CMOS 555 will work at lower voltages.

Michael

 

[Tim Wescott]

On Mon, 13 Feb 2012 22:51:57 -0500, Michael Black wrote:

On Tue, 14 Feb 2012, Phil Allison wrote:

"Adam Funk"


When I supply the whole circuit with 3 V


** Where does it say a 555 will work at 3 volts??

IIRC, the range is 5 to 15 volts.

Yes, and that was the obvious thing I noticed about the post.

I've never actually tried the 555 at a lower voltage.

Perhaps the CMOS 555 will work at lower voltages.

Dang. I missed that point.

I checked on DigiKey, and there's a butt-load of timers with '555' in
their names, many that operate down below 3V. One (the ZSCT1555 by Zetex)
even claims to work down to 0.9V.

But, as Phil will point out amid tiresomely repetitive swear-words if I
don't mention it, they're not NE555 chips, which, of course, is what the
OP must have meant even if he didn't say, because that's what Phil
assumed.

And the SE/NE555 is only specified down to 4.5V

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

 

[Jasen Betts]

On 2012-02-13, Adam Funk <a24061@ducksburg.com> wrote:

I wired up a 556 (two 555 timers on one chip) as follows:

which 556? they are not all the same.

Timer A:
astable circuit with equal mark & space width,
R = 267 Ί, C = 1000 ¾F (electrolytic with 25 V rating),
output: 320 Ί in series with an LED,
also tied to the reset pin on Timer B

Timer B:
same astable timing arrangement,
R = 100 k Ί, C = 10 nF (non-electrolytic),
output: piezo speaker in series with a resistor

[works off 9v]

When I supply the whole circuit with 3 V (two AAAs) instead, however,
(and reduce the resistance in series with the LED accordingly), the
LED stays on all & the speaker whistles all the time.

Some 556s need a 4.5v supply to function correctly.

My questions:

Is tying the output of timer A to the reset pin of timer B the most
correct way to switch B on and off with A?

it seems perfectly acceptable
there are several other ways to get a similar result.

One of the books of 555 circuits says that electrolytic capacitors
only work properly as capacitors above 10% of their rated voltage. Is
this why timer A doesn't work on a 3 V supply?

I've never heard of that, I've used a 250V capacitor on a 9V circuit
before with no obvious problems.

Even with the 9 V supply, the LED doesn't go completely off when the
speaker does --- it's just noticeably dimmer than when the speaker is
on. Why?

possibly pin 7 is not connected battery negative

--
⚂⚃ 100% natural

--- Posted via news://freenews.netfront.net/ - Complaints to news@netfront.net ---

 

[Jasen Betts]

On 2012-02-14, Phil Allison <phil_a@tpg.com.au> wrote:

"Adam Funk"


When I supply the whole circuit with 3 V


** Where does it say a 555 will work at 3 volts??

IIRC, the range is 5 to 15 volts.

the CMOS versions will usually run from a lower voltage,
fairly weak in the output stage though

eg: http://www.ti.com/product/tlc556


--
⚂⚃ 100% natural

--- Posted via news://freenews.netfront.net/ - Complaints to news@netfront.net ---

 

[Phil Allison]

"Jasen Betts" <jasen@xnet.co.nz>


** FUCK OFF to HELL !!

you bullshitting, putrid pile of Kiwi sheep dung !!!

 

[Adam Funk]

On 2012-02-14, Tim Wescott wrote:

On Mon, 13 Feb 2012 20:28:58 +0000, Adam Funk wrote:

I wired up a 556 (two 555 timers on one chip) as follows:

Timer A:
astable circuit with equal mark & space width, R = 267 Ί, C = 1000 ¾F
(electrolytic with 25 V rating), output: 320 Ί in series with an LED,
also tied to the reset pin on Timer B

Timer B:
same astable timing arrangement,
R = 100 k Ί, C = 10 nF (non-electrolytic), output: piezo speaker in
series with a resistor

R = 267 is asking for a lot of current from the chip. You may want to
try using a 2.67k resistor and a 100uF cap, or even a 26.7k and a 10uF.

Now I'm not sure where that number came from. I just checked what I'd
left on the breadboard and it's 10 kΊ. (The book also recommends
using R between 1 kΊ and 1 MΊ.)

Also, an astable multivibrator with a 555 uses two resistors and one cap
to set the frequency and duty cycle -- what's the other resistor value?

Have you bypassed the control inputs on both timers?

The circuit I was using (on both timers, but with different R & C
values) was taken from the book _IC 555 Projects_ as follows:

Vcc to the Vcc pin

Vcc connected to reset on timer A

output connected to the top of R

bottom of R connected to trigger, threshold, and top of C

bottom of C and ground pin connected to ground

output of timer A connected to reset on timer B

discharge pin unconnected on both timers

with the description "equal mark space ratio" and a total period of
T = 1.4 × R × C.


--
Bob just used 'canonical' in the canonical way. [Guy Steele]

 

[Adam Funk]

On 2012-02-14, Tim Wescott wrote:

On Mon, 13 Feb 2012 22:51:57 -0500, Michael Black wrote:
On Tue, 14 Feb 2012, Phil Allison wrote:
"Adam Funk"

When I supply the whole circuit with 3 V

** Where does it say a 555 will work at 3 volts??
IIRC, the range is 5 to 15 volts.

Yes, and that was the obvious thing I noticed about the post.

I've never actually tried the 555 at a lower voltage.

Perhaps the CMOS 555 will work at lower voltages.

Dang. I missed that point.

I checked on DigiKey, and there's a butt-load of timers with '555' in
their names, many that operate down below 3V. One (the ZSCT1555 by Zetex)
even claims to work down to 0.9V.

But, as Phil will point out amid tiresomely repetitive swear-words if I
don't mention it, they're not NE555 chips, which, of course, is what the
OP must have meant even if he didn't say, because that's what Phil
assumed.

Thanks to all of you. I checked the data sheet for what I have (TI
NE556) and the recommended operating range is 4.5 to 16 V.


--
In the 1970s, people began receiving utility bills for
-ÂŁ999,999,996.32 and it became harder to sustain the
myth of the infallible electronic brain. (Stob 2001)

 

[Tim Wescott]

On Wed, 15 Feb 2012 21:35:44 +0000, Adam Funk wrote:

On 2012-02-14, Tim Wescott wrote:

On Mon, 13 Feb 2012 20:28:58 +0000, Adam Funk wrote:

I wired up a 556 (two 555 timers on one chip) as follows:

Timer A:
astable circuit with equal mark & space width, R = 267 Ί, C = 1000 ¾F
(electrolytic with 25 V rating), output: 320 Ί in series with an LED,
also tied to the reset pin on Timer B

Timer B:
same astable timing arrangement,
R = 100 k Ί, C = 10 nF (non-electrolytic), output: piezo speaker in
series with a resistor

R = 267 is asking for a lot of current from the chip. You may want to
try using a 2.67k resistor and a 100uF cap, or even a 26.7k and a 10uF.

Now I'm not sure where that number came from. I just checked what I'd
left on the breadboard and it's 10 kΊ. (The book also recommends using
R between 1 kΊ and 1 MΊ.)


Also, an astable multivibrator with a 555 uses two resistors and one
cap to set the frequency and duty cycle -- what's the other resistor
value?

Have you bypassed the control inputs on both timers?

The circuit I was using (on both timers, but with different R & C
values) was taken from the book _IC 555 Projects_ as follows:

Vcc to the Vcc pin

Vcc connected to reset on timer A

output connected to the top of R

bottom of R connected to trigger, threshold, and top of C

bottom of C and ground pin connected to ground

output of timer A connected to reset on timer B

discharge pin unconnected on both timers

with the description "equal mark space ratio" and a total period of T =
1.4 × R × C.

You mention in another response that you're using an NE555, which has
(I'm pretty sure) a TTL-style totem-pole output, which, in turn, does not
pull the output all the way to VCC.

That circuit will work DANDY on a CMOS version of the 555, because you
can pretty much count on the output going nearly to the rails.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

 

[Adam Funk]

On 2012-02-14, Jasen Betts wrote:

On 2012-02-13, Adam Funk <a24061@ducksburg.com> wrote:

Even with the 9 V supply, the LED doesn't go completely off when the
speaker does --- it's just noticeably dimmer than when the speaker is
on. Why?

possibly pin 7 is not connected battery negative

Right, the discharge pin is not connected at all in this circuit.

Thanks.


--
When a man tells you that he got rich through hard work, ask him
whose? --- Don Marquis

 

[Jasen Betts]

On 2012-02-16, Adam Funk <a24061@ducksburg.com> wrote:

On 2012-02-14, Jasen Betts wrote:

On 2012-02-13, Adam Funk <a24061@ducksburg.com> wrote:

Even with the 9 V supply, the LED doesn't go completely off when the
speaker does --- it's just noticeably dimmer than when the speaker is
on. Why?

possibly pin 7 is not connected battery negative

Right, the discharge pin is not connected at all in this circuit.

pin 7 is the groun pin of a 556.
-

--
⚂⚃ 100% natural

--- Posted via news://freenews.netfront.net/ - Complaints to news@netfront.net ---

 

[Adam Funk]

On 2012-02-18, Jasen Betts wrote:

On 2012-02-16, Adam Funk <a24061@ducksburg.com> wrote:
On 2012-02-14, Jasen Betts wrote:

On 2012-02-13, Adam Funk <a24061@ducksburg.com> wrote:

Even with the 9 V supply, the LED doesn't go completely off when the
speaker does --- it's just noticeably dimmer than when the speaker is
on. Why?

possibly pin 7 is not connected battery negative

Right, the discharge pin is not connected at all in this circuit.


pin 7 is the groun pin of a 556.

I assumed Jasen was refering to the equivalent 555 pin numbers.

But in the circuit I was using, 556 pin 7 was connected to the battery
negative (and 14 "Vcc" was connected to the positive).


--
Mathematiker sind wie Franzosen: Was man ihnen auch sagt, Ăźbersetzen
sie in ihre eigene Sprache, so daß unverzüglich etwas völlig anderes
daraus wird. [Goethe]

 

[Adam Funk]

On 2012-02-15, Tim Wescott wrote:

You mention in another response that you're using an NE555, which has
(I'm pretty sure) a TTL-style totem-pole output, which, in turn, does not
pull the output all the way to VCC.

That circuit will work DANDY on a CMOS version of the 555, because you
can pretty much count on the output going nearly to the rails.

Thanks for that tip! If I get around to doing anything serious, I
might buy some of those.


--
I heard that Hans Christian Andersen lifted the title for "The Little
Mermaid" off a Red Lobster Menu. [Bucky Katt]