----- Original Message ----- 
From: "Jinx" <joecolquitt@clear.net.nz>
To: "Microcontroller discussion list - Public." <piclist@mit.edu>
Sent: Monday, September 22, 2008 8:08 PM
Subject: Re: [EE] Would Vcc affect frequency of Astable Multivibrator?


>> a well known 3 gate version that always starts
>
> Ring-of-three ?
>
> Don't know about the start-up reliability but it does have an extra
> gain stage that produces a cleaner output (eg better for clocks and
> counters)
>
 Note:  Any "ring of three" (or any odd number) of CMOS inverters will 
self-oscillate.  One problem is that the more (active) gates there are in 
sequence the greater the power consumption will be.  A better bet might be 
to use a HCMOS Schmitt trigger package, such as a 74HC14 Hex Inverter or a 
74HC132 Quad Schmitt triggered NAND.

    Either of these can be configured as a self-starting astable using one 
resistor and one cap.  Unused inputs must be tied Hi or Lo to minimize power 
consumption.  Because of the relatively proportional trip levels the 
frequency should be fairly stable over a range of voltages.

Luck, Bruce 

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