Timing Circuit
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From: John B on 30 Jan 2006 08:28 On 30/01/2006 the venerable PN2222A etched in runes: > > "Jimbo" <James.Wyninegar(a)gmail.com> wrote in message > news:1138570597.321014.296350(a)z14g2000cwz.googlegroups.com... > > 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? > > > > The first 1 or 2 digits is usually the heater voltage. > > Regards > PN2222A 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
From: Winfield Hill on 30 Jan 2006 09:00 Winfield Hill wrote... > > 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 >> fluctations will not be a worry. ... > > 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, > we get C = 0.027uF, ... 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
From: John Fields on 30 Jan 2006 10:34 On 30 Jan 2006 06:00:47 -0800, Winfield Hill <Winfield_member(a)newsguy.com> wrote: >Winfield Hill wrote... >> >> 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 >>> fluctations will not be a worry. ... >> >> 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, >> we get C = 0.027uF, ... > > 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. -- John Fields Professional Circuit Designer
From: John Fields on 30 Jan 2006 12:46 On Mon, 30 Jan 2006 09:34:00 -0600, John Fields <jfields(a)austininstruments.com> wrote: >On 30 Jan 2006 06:00:47 -0800, Winfield Hill ><Winfield_member(a)newsguy.com> wrote: > >>Winfield Hill wrote... >>> >>> 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 >>>> fluctations will not be a worry. ... >>> >>> 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, >>> we get C = 0.027uF, ... >> >> 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. --- 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. -- John Fields Professional Circuit Designer
From: Jimbo on 30 Jan 2006 13:58
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 6811 or 6812? |