I need to design a circuit that I can tell it to start (digitally), and 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
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.
formatting link
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,
formatting link
formatting link
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.
formatting link
This IC is also heavily manufactured and used. Here're Fairchild and TI's datasheets,
formatting link
formatting link
BTW, you can get free samples of both ICs from ON Semi. And TI.
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 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.
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?
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.
========== 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?
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"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
On 30/01/2006 the venerable PN2222A etched in runes:
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.
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.
--
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.
microcontroller? I've programmed them before but I don't know of any 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
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.