Re: Want independant pulse width variation on + and - side of gnd;square wave of about 1kHz
jtaylor
Spehro Pefhany <spef...@interlogDOTyou.knowwhat> wrote in message
news:7jetm01ar7l285qog...@4ax.com...
> On Thu, 14 Oct 2004 14:28:22 -0300, the renowned "jtaylor"
> <jta...@hfx.deletethis.andara.com> wrote:
>
> >
> >John Popelish <jpop...@rica.net> wrote in message
> >news:416EA3A9...@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%)?
Rich Grise
> On Thu, 14 Oct 2004 15:06:03 -0300, the renowned "jtaylor"
> <jta...@hfx.deletethis.andara.com> wrote:
>>
>>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.
>
I'd have done it with discretes. Eight of them, to be exact. (maybe ten,
if you don't want Rb to go to zero. ;-) )
Cheers!
Rich
CFoley1064
>Unless
>you want to change something else, this should do the job (view in fixed font
>or M$ Notepad):
>
>
>
> +5V
> |
> .-. +5V
> | | | +5V 1/4 4066
> | | .-. | .-----.
> '-' 1/2 LM393| | | | |
> | +5V| | '---oI Oo-.
> .-. |\| '-' | C | |
> | |<--------|-\ | '--o--' |
> ___ | | | >-o-----------' |
> .--|___|----. '-' .-----|+/ |
> | +5V | | | |/| |
> | | | | | -5V o--o
> | |\ | | | | |
> .---o---|H>O----' o-----------o +5V | |
> | | |/ | | | | 1/4 4066 | .-.
> | | | | | | .-. .-----. | | |
> | --- | | .----o | | | | | | | |
> | --- -5V | | | | +5V| | .--oI Oo-' '-'
> | | 1/6 74C14 | | .-. | |\| '-' | | C | |
> | | |=== | |<--|-----|-\ | | '--o--' ===
> | | |GND | | | | >-o-----|-----' GND
> | -5V | '-' '-----|+/ |
> | | | |/| |
> |------------------' .-. -5V -5V
> | | 1/2 LM393
> | |
> '-'
> |
> -5V
>created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de
>
>Not elegant at all, but it will do the job. Split supplies, matched +/-5V.
>H
>is 1/6 of a 74C14, which should oscillate at the frequency you determine with
>the R and C. DC level of oscillations should be nearly 0V. Amplitude of
>oscillation with +--5V supplies with a C14 (don't use a 40106 or other CMOS
>schmitt trigger IC -- they're made differently and have lower hysteresis
>voltage and less precise switching points) should be about +2V to -2V. The
>two
>comparators pick off the signal from the cap, and are compared with the pot
>settings. You can use those pots to set the time for +5V out (up to 50%) and
>-5V out (up to 50%). These outputs go to half a 4052 or 4066, which are
>analog
>switches that turn on the +5V or -5V output. When neither is on, you have 0V
>(resistor to GND).
>
>One immediately apparent way to make this better would be to use a quad op
>amp
>instead of the dual comparator and the C14, to ensure symmetry around GND for
>the oscillator and design in a fixed amplitude even if the supplies are not
>matched. The OP is talking about a couple of KHz, so the rise time of a good
>op amp shouldn't be too significant here. Use two of the other 4 op amps as
>comparators, and lose the pullup resistors.
>
And, if you want the + part to be able to go to 100% or the - part to be able
to go to 100%, you'll have to play with the pots a little. This is the basic
idea, though. Oh, yes. As always, you can use a PIC to drive these outputs at
any duty cycle you choose. If you need some power, just connect a rail-to-rail
op amp as a voltage follower at the output.
Chris
Andrew Holme
> Subject says most of it; power requirements are small, frequency and some
> pulse width drift/variation is no problem...
Two monostables?
| |
\ \
/ /
+--> \ VR1 +--> \ VR2
| / | /
| | | |
+----+ +----+
| |
+----o----+ +----o----+
| _ | | |
+--o CLK Q o-----o CLK Q o----+-------> out
| | | | | |
| +---------+ +---------+ |
| |
+---------------------------------+
Andrew Holme
> Subject says most of it; power requirements are small, frequency and some
> pulse width drift/variation is no problem...
Ignore my previous post - two monos might not start properly. Try this:
|\
+------| >O--------------+---> out
| |/ |
| Schmitt |
| |
| +---+ |
| | | |
| _V_ | |
+-----|___|-+---|<-------+
| VR1 D1 |
| |
| +---+ |
| | | |
| _V_ | |
+-----|___|-+--->|-------+
| VR2 D2
|
---
--- C
|
|
===
GND
Spehro Pefhany
(CFoley1064) wrote:
>>Subject: Re: Want independant pulse width variation on + and - side of
>>gnd;square wave of about 1kHz
>>From: Spehro Pefhany spef...@interlogDOTyou.knowwhat
>>Date: 10/14/2004 1:58 PM Central Daylight Time
>>Message-id: <j4htm09e04voj3s78...@4ax.com>
>
><snip>
>>>
>>>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
>
>I believe this is something close to what Mr. Pefhany is talking about. Unless
>you want to change something else, this should do the job (view in fixed font
>or M$ Notepad):
<snip>
That's pretty simple. I was thinking of something more along the lines
of:
+5V +5V
o o
| |
| |
.-------. .-------.
| 4066 | Pin 6,2 | 4066 |
State 0-----| 1/4 | LMC555 | 1/4 |---- State 2
'-------' o '-------'
| | |
Ton + .-. | .-. Ton-
| |<-----+------>| |
| | | | |
Toff + '-' --- '-' Toff-
| --- |
.-------. | .-------.
| 4066 | o | 4066 |
State 1-----| 1/4 | -5V | 1/4 |---- State 3
'-------' '-------'
| |
| |
o o
-5V -5V
Plus the 555 itself, the decoding logic for the states and the output.
The above should require no adjustment (though if it was required, a
trim could be made using pin 5 on the 555, either a single trim to
compensate for capacitor variation or a dual-level trim to compensate
for the differences in the pot elements). It should be very linear
with pot resistance. Also no other passive components except perhaps
an output resistor to ground depending on how that bit is done. Using
1/2 a 4052 and a 4-resistor network could take care of the decoding
and the second half could drive the output positively to each of the
three levels. So, parts count:
1 - 4066
1 - LMC555
1 - 4052
1 - 4013 (1/2 used)
1 - 4-resistor network
2 - pots
1 - capacitor
-----------
8 (+ bypass caps)
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
sp...@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
John Fields
<jta...@hfx.deletethis.andara.com> wrote:
>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%)?
---
Here's a 1000 cycle square wave:
|<------500盜------>|<------500盜------>|
___ ___________________
|___________________| |_____
Then, plugging in your curious timing units, we get:
|<-----1/2000s----->|<-----1/2000s----->|
___ ___________________
|___________________| |_____
|----|----|----|----|----|----|----|----|
-->| |<---1/8000s
And, finally, if what you're asking for, above, is this:
___ ___________________
SQIN |___________________| |_____
____
+5 ___ _________| |______________
OUT |_________| |_____
-5
TIME |----|----|----|----|----|----|----|----|
-->| |<---1/8000s
This will get it for you:
+5V
|
+----+-----+--------------+
| | | |
+5V | | +--+--+ |
| +->[RV1] | | VDD | |
+--+--+ | | | |4538A| |
| Vcc | +----+-------|RC | |
|7555 | | | | | |
| OUT|---+----+-------|-------|IN | |
| | | | | | |__ _| E
| | [R1] | [C2] +-O|IN Q|---[1K]---B 2N4403
| __| | | | | | C
| TR|---+ | | | | |
| | | | | +-----+ [100R]
| TH|---+ | -5V |
| GND | | | |
+--+--+ [C1] | +--------+-->OUT
| | | | |
-5V -5V | +5V | [1000R]
| | +-----+ [100R] |
| +->[RV2] | | | GND(0V)
| | | |4538B| C
| +----+-------|RC Q|---[1K]---B 2N4401
| | | | E
| [C3] +--|IN | |
| | | |__ | |
+--------------O|IN | |
| | | | |
| | | VEE | |
| | +--+--+ |
| | | |
+----+-----+--------------+
|
-5
Select R1 and C1 to give you a 1000Hz output from the 7555.
Select RV1C2 and RV2C3 to give you a maximum pulse output width from
either 4538A or 4538B of 500盜. If you go over 500盜 for either one,
or the output frequency from the 7555 is >1000Hz or the output of
either half-period from the 7555 is <500盜, The output totem-pole
will short, you'll get pretty close to zero volts out of the output,
and the only thing limiting the current through the transistors will
be the two 100 ohm resistors. With 10V across the transistors, if
they're saturated the resistors will limit the current through them to
about 50mA, which is no big deal but, if you need/want to change the
resitor values in order to get more current into your load, you'll
want to be careful not to fry the two output transistors with an
inadvertent input drive overlap.
The way it's set up now, with only the 1000 ohm resistor for a load,
the outout voltage will go from a high of +4.5V with 2N4403 on and the
2N4401 off, to ~0V with them both off, (or on!) to a low of -4.5V
with the 2N4403 off and the 2N4401 on.
--
John Fields