[sdiy] inexpensive chips for oscillators (still learning...)

[Scott Gravenhorst]

Dave Kendall <davekendall at ntlworld.com> wrote:
>You probably know this already, but if using 555s, go for CMOS versions 
>(7555, TLC555 etc) which draw *far* less power. It's my understanding 
>that the regular 555 can cause problems with power consumption when 
>switching.

The datasheet I have for the 7555 has current graphs that show the difference between
the bipolar 555 and the CMOS 7555 while they are switching.  The difference is
amazingly large.

In fact, the PAiA Fatman had been designed using bipolar 555 timers for the two VCOs.
 Unmodified, it has a notable problem of soft synching the VCOs when they are close
in pitch.  This is because even though the 555 is fed power through a 100 ohm
resistor with a 100 uF cap to -12V, there is still a significant current spike at
switching time that propogates to the other VCO.  A fix was designed by PAiA which
replaces the 100 ohm resistor with an LED.  Another fix that I found after learning
about the 7555 was to simply replace the bipolar 555 with CMOS 7555.  The two fixes
work about as well as each other, but I prefer the 7555 fix over the LED fix.

+1 for 7555.

And you can go to www.paia.com and look at the schematic for how they turned a 555
(or 7555) timer into a VCO.  It is a _linear_ VCO, but enterprising lovers of expo
could probably convert the VCO's voltage to current converter to use expo instead of
linear pitch CV.

>On Sep 26, 2011, at 17:21, Bob K wrote:
>
>> Hi everyone,
>>
>> New here.  Hi.  How's everybody?  Fine?  That's good.
>>
>> After skimming through the two Forrest Mimms books I have and "Make:
>> Electronics", both books are making a point that 555 and 556 chips are
>> a good (and cheap) start for breadboarding oscillators.
>>
>> I'm planning on a bulk purchase (bulk meaning around 10) of the above
>> mentioned chips and was wondering if there are any other cheap chips
>> along the lines of the 555 and 556 that can be used for oscillators?
>> I'm going to search online for advice as well but thought I'd run this
>> question by everybody here.
>>
>> Thanks.
>>
>> -Bob
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-- ScottG
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-- Scott Gravenhorst
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