Timing Circuit
Jimbo
then it will tell me when 10 minutes have passed. I just need to be
pointed in the right direction. What's the difference bewteen a
timer/clock/counter. I have a good understanding of circuit theory but
does anyone know of a good IC that can be surface mounted (and is
cheap) that I shoulod use. Any help or tips are greatly appreciated
Fred Bloggs
Go to http://www.ti.com and enter 74HC4060 in search box.
Jimbo
through for me.
Winfield Hill
>
> THANKS! This chip looks perfect. Good ol TI always seems
> to come through for me.
The 74hc4060 is an attractive chip with its on-board oscillator,
but you should be aware cmos inverter-oscillators aren't very
predictable (from IC to IC), nor very stable after the timing
components are adjusted for your time delay. If you're only
looking for a rough 10 minutes, fine, but if you want a semi-
accurate 10 minutes you may prefer to use a second oscillator
IC, such as a cmos 555, etc. Also, the 'hc4060 isn't the most
attractive choice, because its 2^(14-1) = 8192-cycle timing
requires a pretty low oscillator frequency for 10 minute timeout
(13.65 Hz). Other parts have a higher divider ratio, such as
Motorola's (now ON Semiconductor) mc14536, with 24 bits.
The mc14536 also has an onboard oscillator, in case you still
want to give that a try. I first started using the '4536 in
the early 70s, and shipped thousands of instruments that relied
on its cool 4-bit divider-select feature. We also featured the
'4536 in our "hour of power" circuit in AoE (page 972), although
I'm not happy with circuit we show there. $0.76 at DigiKey,
very nice. http://www.onsemi.com/pub/Collateral/MC14536B-D.PDF
BTW, TI also makes the '4536, as their cd4536B, if you prefer
them. ST calls it the hcf4536B. The TI and ST datasheets,
which were modeled after the Intersil/Harris datasheet, do a
better job of showing how to use the powerful timer functions,
http://focus.ti.com/general/docs/lit/getliterature.tsp?genericPartNumber=cd4536b
http://www.st.com/stonline/products/literature/ds/4901/hcf4536.pdf
Alternately, if you want to stick with a 16-bit IC, ON Semi's
mc14541 is more attractive than the '4060, because it features
an output flip flop with a polarity selection feature (and it
also has an onboard oscillator), only $0.50 to 0.58 at DigiKey.
http://www.onsemi.com/pub/Collateral/MC14541B-D.PDF This IC is
also heavily manufactured and used. Here're Fairchild and TI's
datasheets, http://www.fairchildsemi.com/ds/CD/CD4541BC.pdf
http://focus.ti.com/general/docs/lit/getliterature.tsp?genericPartNumber=cd4541b
BTW, you can get free samples of both ICs from ON Semi. And TI.
--
Thanks,
- Win
Jimbo
that will work with a +/- 30 seconds or so. I'm assuming that any
change in performance based upon manufacturer and/or temperature
fluctations will not be a worry. Also, I don't really care as to the
number of bits the chip has for an output. I'm thinking I'll just run
the desired outputs through an AND that sets a S-R flip/flop. I'm sure
there is a better way of doing this and once I start with the design
maybe I'll come across some features that can help me cut down the need
for extra circuirty. Perhaps that's what the mc14541 does. Doing this
stuff in actual practice is quite a bit different than what I did for
school. It seems that there are so many permutations of doing the same
thing it's dizzing. It seems almost impossible to find the absolute
cost effective and most efficent way of doing something. Too many
options and not enough time.
THANKS FOR YOUR HELP!
Jimbo
Jimbo
Is there a "system" for the naming of the IC out there? I keep reading
things that tend to "hint" that there is a systematic way of naming
these things. Isn't the formation usually "LETTERS" + "NUMBER" +
"LETTERS". Have any idea as to the method these things are named?
Fred Bloggs
Jimbo wrote:
> Thanks for the info. As far as accuracy, I'm looking for something
> that will work with a +/- 30 seconds or so.
That is only 5%.
> I'm assuming that any
> change in performance based upon manufacturer and/or temperature
> fluctations will not be a worry. Also, I don't really care as to the
> number of bits the chip has for an output. I'm thinking I'll just run
> the desired outputs through an AND that sets a S-R flip/flop.
You don't need to do that unless you want the timeout to be
programmable, in which case none of the suggested parts are that good.
> I'm sure
> there is a better way of doing this and once I start with the design
> maybe I'll come across some features that can help me cut down the need
> for extra circuirty. Perhaps that's what the mc14541 does. Doing this
> stuff in actual practice is quite a bit different than what I did for
> school. It seems that there are so many permutations of doing the same
> thing it's dizzing. It seems almost impossible to find the absolute
> cost effective and most efficent way of doing something. Too many
> options and not enough time.
Once you get close, the differences in implementation become negligible.
Pooh Bear
Jimbo wrote:
This has to be a classic job for a baby microcontroller. Typically a tiny
PIC.
That involves learning about microcontrollers and doing programming though.
Doing it in hardware is 'easier' for a beginner but will use lots of parts
in comparison. It *won't* be 'just an IC' although the microcontroller
method can be.
Graham
Winfield Hill
> Jimbo wrote:
>> Thanks for the info. As far as accuracy, I'm looking for
>> something that will work with a +/- 30 seconds or so.
>
> That is only 5%.
Acckk!! You're right, I mentally added in an extra factor of
60 and came up with a moderately-painful 1:1200 design. Hah!
--
Thanks,
- Win
Winfield Hill
==========
Oops, I made a mistaken post, with mental calculations off by 60x.
Let's leave it here, below, but for sake of discussion let's assume
that Jimbo's requirement was for a 0.5-second, 0.1% accuracy. :-)
In practice, with his 5% spec, he can use a '4541 IC with a 294k 1%
resistor and a 27nF 5% film capacitor. Or better, 2% caps like the
nice Panasonic parts offered by DigiKey. That way tolerances will
be in the IC, and Jimbo may be able to dispense with adjustments.
===========
Jimbo, your 30-second spec is one part in 1200, within the range of
analog relaxation-oscillator stability with RC components, provided
they are properly chosen. A 16-bit divider (15-bits in timer mode)
like a '4541 will have its oscillator running at 32768/600 = 54.6Hz,
which isn't bad. Using f = 1 / 2.3 RC, and R = 249k plus a 100k pot,
we get C = 0.027uF, a moderate-value capacitor for which small stable
versions may be practical. Still, I'm tempted to suggest instead an
8-pin uP with a 32kHz resonator. Have you considered that possibility?
--
Thanks,
- Win
Spehro Pefhany
<James.W...@gmail.com> wrote:
Check out the 4536 as well. But a single 8-pin microcontroller can
give you the required accuracy with no external parts, or 10x better
with one external part. You would have to program it.
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
sp...@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
Pooh Bear
Jimbo wrote:
There is next to no sense at all in it.
The first few numbers/letters may tell you something but not a lot.
Graham
PN2222A
"Jimbo" <James.W...@gmail.com> wrote in message
news:1138570597.3...@z14g2000cwz.googlegroups.com...
The first 1 or 2 digits is usually the heater voltage.
Regards
PN2222A
PN2222A
"Jimbo" <James.W...@gmail.com> wrote in message
news:1138570597.3...@z14g2000cwz.googlegroups.com...
The first 1 or 2 digits is usually the heater voltage.
Regards
PN2222A
Alan
wrote:
so you have a 300mA heater??
--
Sell your surplus electronic components at
http://ozcomponents.com
Search or browse for that IC, capacitor,
crystal or other component you need.
John B
Actually the first letter is the heater voltage and the next one or two are the construction. For
example ECC83 is a 6.3VAC heater dual triode and ECF86 is 6.3VAC heater triode/pentode.
--
John B
Delete 'spam blocker' to reply direct
Winfield Hill
>
> Jimbo wrote...
>>
>> Thanks for the info. As far as accuracy, I'm looking for something
>> that will work with a +/- 30 seconds or so. I'm assuming that any
>> change in performance based upon manufacturer and/or temperature
>
> In practice, with his 5% spec, he can use a '4541 IC with a 294k 1%
> resistor and a 27nF 5% film capacitor. Or better, 2% caps like the
> nice Panasonic parts offered by DigiKey. That way tolerances will
> be in the IC, and Jimbo may be able to dispense with adjustments.
> they are properly chosen. A 16-bit divider (15-bits in timer mode)
> like a '4541 will have its oscillator running at 32768/600 = 54.6Hz,
> which isn't bad. Using f = 1 / 2.3 RC, and R = 249k plus a 100k pot,
Actually, I take that back, Jimbo no doubt will need a pot, even
if he does use a 2% capacitor. The chip's timing factor of 2.3
has a tolerance as well, although none of the manufacturers will
give you a hint as to what it is. NSC's cd4541B datasheet does
have a frequency-deviation graph from which one can see about 2%
drop vs supply from 15 to 10V, and another -8% for 5V, along with
a 1% increase for a 50-deg C increase in temperature. One useful
thing we can take from this graph is that for operation near 5V
one should use a constant of 2.5 instead of 2.3 in the equation.
--
Thanks,
- Win
John Fields
<Winfiel...@newsguy.com> wrote:
---
The easy way out in order to essentially remove the power supply and
temperature dependency of the chip, (without resorting to a crystal
or ceramic resonator) is to use a 7555 an an astable to determine
the clock frequency. With an initial worst-case accuracy of +/- 5%,
and your suggested 2% cap and 1% resistor, that comes out to +/- 8%.
However, using a low tempco rheostat and cap to set the center
frequency takes out the uncertainty due to the chip's initial
accuracy, leaving only the cap's tolerance and the pot's tempco to
deal with (assuming the cap's tolerance includes its tempco), so you
wind up with, essentially, a 2% machine.
--
John Fields
Professional Circuit Designer
John Fields
---
Silly me.
You wind up with a machine that's right on the money plus or minus
the tempco's and the variation due to the power supply sensitivity.
Jimbo
that are as cheap as these other chips. Also, I'm doing this to pay my
way through grad school and I'm working with a very small upstart so
any development boards/software is out of the question becuase of the
price. This is going to be a "large volume"/"low margin" product so
every extra dollar we can squeeze out of the design will have a huge
impact on the bottom line. Are you thinking about something like the
6811 or 6812?
Barry Lennox
wrote:
I built quite large numbers of a semi-smart battery charger that used
the SMD 4541 timer to generate 14 hours on time. With a decent R and C
in the oscillator, the end time never varied by more than +/- 3-4
minutes, or better than 1%. The divider chain lets you select divide
by 256,1024,8192 or 65636, and it has a couple of neat control
features, dirt cheap too, IIRC, about $1 each.
Barry Lennox
Jimbo
Microcontroller there is probably a lot of other logic I can replace as
well. I'll have to sleep on that one. Perhaps I'll design the product
both ways and then make a comparsion. I don't think I have enough
experience at this point to simply make a "judgment call".
Rich Grise
Well, you've got a lot of options:
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=74
And they show the list prices in their parametic charts, too.
Have Fun!
Rich
Spehro Pefhany
<James.W...@gmail.com> wrote:
There are sub-dollar parts (qty. 100) that can exceed your accuracy
spec with no external parts (internal calibrated RC oscillator) and
(most important) NO manual trimming or accuracy testing. By using an
8-pin part with an external resonator you could get 0.5% accuracy for
about 65 cents (qty. 100)- eg. ATtiny11. You'd have a few I/Os left to
play with, can add additional functionality cheaply, and the circuit
will become more difficult to copy. Seems like a no-brainer. If the
startup will pay you something for the couple of weeks it will take
you to figure this stuff out (almost all learning curve), you'll both
be ahead.
Peter Bennett
<spamj_ba...@blockerzetnet.co.uk> wrote:
But an ECC 83 is a European 12AX7, which has a centre-tapped 12 volt
filament.
--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
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Winfield Hill
>
> There are sub-dollar parts (qty. 100) that can exceed your accuracy
> spec with no external parts (internal calibrated RC oscillator) and
> (most important) NO manual trimming or accuracy testing. By using an
> 8-pin part with an external resonator you could get 0.5% accuracy for
> about 65 cents (qty. 100)- eg. ATtiny11. You'd have a few I/Os left to
> play with, can add additional functionality cheaply, and the circuit
> will become more difficult to copy. Seems like a no-brainer. If the
> startup will pay you something for the couple of weeks it will take
> you to figure this stuff out (almost all learning curve), you'll both
> be ahead.
I second that.
--
Thanks,
- Win
Ken Smith
John Fields <jfi...@austininstruments.com> wrote:
[....]
>However, using a low tempco rheostat and cap to set the center
>frequency takes out the uncertainty due to the chip's initial
>accuracy, leaving only the cap's tolerance and the pot's tempco to
>deal with (assuming the cap's tolerance includes its tempco), so you
>wind up with, essentially, a 2% machine.
Use a thru hole film cap. After it is installed, cycle the whole PCB
between the hot box and the freezer a few times befor you adjust the pot.
The quick warm up and cool down work the stresses out of the parts and get
the initial drift mostly over with before you tweek the pot.
If you do 90% of a resistor's value with a fixed resistor and the last 10
with a pot, you can reduce the tempco effects in the pot and make the
tweeking easier.
--
--
kens...@rahul.net forging knowledge
Phil Hobbs
> If you do 90% of a resistor's value with a fixed resistor and the last 10
> with a pot, you can reduce the tempco effects in the pot and make the
> tweeking easier.
>
The wiper connection is liable to become unreliable, so it's usually
better to combine pots and fixed resistors in parallel, or better,
series-parallel, to confine the adjustment range. Either way, the thing
will still work at some level if the wiper opens.
Cheers,
Phil Hobbs
Ken Smith
It depends on whether a little out of spec is better than completely
stopped.
You could also use one of those EEProm based digital pots. In 555 like
circuits, changing the effective voltage source for the resistor also can
be used to trim the frequency.
Jimbo
Don Bowey
1138764826....@g43g2000cwa.googlegroups.com, "Jimbo"
<James.W...@gmail.com> wrote:
> What's the "wiper connection"?
>
A new spy novel title? Unless you post a quote of what you are referring
to, it's hard to tell.
Don
Spehro Pefhany
<James.W...@gmail.com> wrote:
>What's the "wiper connection"?
The wiper is the metal bit wot touches the resistance element.
There are actually two sliding contacts involved in most (not all)
pots, a sliding low-resistance connnection to the moving contact and
the wiper contact to the element. Good quality pots and trimpots are
actually extremely reliable in most situations-- billions of them are
made every year. In production situations it's nice to avoid the
labo[u]r of adjusting them, but even that is a mixed blessing as much
of the adjustment process can be an essential part of the test
procedure.