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Electrolytic capacitors & playing with 556 chip

Started by Adam Funk February 13, 2012
I wired up a 556 (two 555 timers on one chip) as follows:

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

Timer B:
same astable timing arrangement,
R = 100 k Ω, 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
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 Ω, C = 1000 µF > (electrolytic with 25 V rating), output: 320 Ω in series with an LED, > also tied to the reset pin on Timer B > > Timer B: > same astable timing arrangement, > R = 100 k Ω, 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
"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
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
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
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 &Omega;, C = 1000 &micro;F (electrolytic with 25 V rating), > output: 320 &Omega; in series with an LED, > also tied to the reset pin on Timer B > > Timer B: > same astable timing arrangement, > R = 100 k &Omega;, 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 -- &#9858;&#9859; 100% natural --- Posted via news://freenews.netfront.net/ - Complaints to news@netfront.net ---
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 -- &#9858;&#9859; 100% natural --- Posted via news://freenews.netfront.net/ - Complaints to news@netfront.net ---

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


** FUCK  OFF  to HELL !!

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











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 &Omega;, C = 1000 &micro;F >> (electrolytic with 25 V rating), output: 320 &Omega; in series with an LED, >> also tied to the reset pin on Timer B >> >> Timer B: >> same astable timing arrangement, >> R = 100 k &Omega;, 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 k&Omega;. (The book also recommends using R between 1 k&Omega; and 1 M&Omega;.)
> 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 &times; R &times; C. -- Bob just used 'canonical' in the canonical way. [Guy Steele]
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 -&pound;999,999,996.32 and it became harder to sustain the myth of the infallible electronic brain. (Stob 2001)