Re: Want independant pulse width variation on + and - side of gnd;square wave of about 1kHz

From: Spehro Pefhany (speffSNIP_at_interlogDOTyou.knowwhat)
Date: 10/14/04 

Date: Thu, 14 Oct 2004 14:58:13 -0400

On Thu, 14 Oct 2004 15:06:03 -0300, the renowned "jtaylor"
<jtaylor@hfx.deletethis.andara.com> wrote:

>
>Spehro Pefhany <speffSNIP@interlogDOTyou.knowwhat> wrote in message
>news:7jetm01ar7l285qog0fso67k4okgc1fbqc@4ax.com...
>> On Thu, 14 Oct 2004 14:28:22 -0300, the renowned "jtaylor"
>> <jtaylor@hfx.deletethis.andara.com> wrote:
>>
>> >
>> >John Popelish <jpopelish@rica.net> wrote in message
>> >news:416EA3A9.6BA8F9E2@rica.net...
>> >>
>> >> How can the positive and negative parts both be 100% (duty cycle?) at
>> >> the same time or 0% at the same time (infinite frequency)?
>> >>
>> >> Or are you saying that you want the on time to be variable from some
>> >> small time to some maximum time and also the off time to be variable
>> >> from some small time to some maximum time and variations in the
>> >> duration of one state does not affect the duration of the other state?
>> >
>> >
>> >Um, no. I want ground in the middle, and the other line to go from say
>+5v
>> >to -5v, at about 1kHz, with the + pulse varying in width, and the - pulse
>> >varying in width.
>>
>> You can consider connecting the "GROUND" pin on the 555 to -5V. It'll
>> never know the difference, you know.
>>
>
>Yes, but how would I get a (say) drop from ground to -5V lasting for
>1/4000th second , returning to 0V for 1/4000th second (1/2 cycle of 1kHz at
>50%) followed by (say) a rise from 0V to +5V lasting for 1/8000th second,
>returning to 0V for 3/8000ths of a scond (1/2 cycle of 1Khz at 25%)?

Okay. If you use a single 555 in astable mode you can steer the
currents through both ends of your two pots to get this effect by
using a FF (eg. 1/2 4013) and 2 complimentary pairs of transistors.

Driving the output to the 3 levels depends on how much drive you need.
One possibility would be to use 1/2 of a 4052. It could also be done
with discretes.

Best regards,
Spehro Pefhany 

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