[Lowfer] A timely question

[Johan H. Bodin]

Bill,

the 4060 oscillator/binary counter is another alternative.

http://www.nxp.com/acrobat_download/datasheets/74HC_HCT4060_CNV_2.pdf

Design the oscillator for 1Hz and use the first 8 counter stages to get a total 
cycle length of 256 seconds. Outputs Q0..Q2 are not connected to any pins but 
you don't need these anyway. If you run the four outputs Q4, Q5, Q6 and Q7 (pins 
5, 4, 6, 14) to a four input OR, NOR, AND or NAND gate, the output will be one 
state when these outputs are all low (or all high) and in the other state when 
they're not. This condition lasts for 16 out of 256 seconds. Not exactly 20 out 
of 260 but perhaps good enough? Of course, the gate can be made from four diodes 
if you wish.

Plain old 4060 CMOS runs from 3..15V
74HC4060 runs from 2..6V
74HCT4060 runs from 5V

73
Johan SM6LKM


Bill Ashlock skrev:
> OK you smarties,
> 
> 
> Here's a question about the old faithfull 555 timer IC that came up the other day when I was on the bench looking at various ways of generating a 4 min ON, 20 second OFF continuous sequence with fairly good accuracy. Due to leakage current constraints the std 555 can handle only a 3.3 meg main timing resistor and therefore one is forced into using electrolytics with  unpredictable ESRs and leakages. Then I recalled running across a CMOS version of the 555 which would make it possible to use high-value resistors along with a 10uf small-sized ceramic capacitor.
> 
> I downloaded a Fairchild spec for the 555CM and to my surprise the applicable leakage currents were not all that low. In fact there was no mention of this being a CMOS chip at all.  I did locate a spec out of a numerous others specs that definitely called out CMOS construction - and the leakage currents were very low. I am not close to my home base so I can't check to see what the designator was. Question is: What are the magic designators from various manufacturers needed to be sure the 555 I am ordering is actually CMOS?
> 
> Thanks
> Bill _______________________________________________
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