Timing Circuit
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From: Jimbo on 29 Jan 2006 10:12 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
From: Fred Bloggs on 29 Jan 2006 10:14 Jimbo wrote: > 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 > Go to http://www.ti.com and enter 74HC4060 in search box.
From: Jimbo on 29 Jan 2006 10:22 THANKS! This chip looks perfect. Good ol TI always seems to come through for me.
From: Winfield Hill on 29 Jan 2006 12:41 Jimbo wrote... > > 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
From: Jimbo on 29 Jan 2006 15:30
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. THANKS FOR YOUR HELP! Jimbo |