Generating this negative pulse?

[Terry Pinnell]

I have a couple of simple 555 monostables, the first to delay the
triggering of the second.
https://www.dropbox.com/s/6uboy3fgd0ixhxa/GenerateNegPulse-1.jpg?raw=1

But I'm struggling to extract the brief -ve pulse required for the Main
mono. I thought it would prove simple. But bread-boarding various
combinations of R, C, diode and NPN or PNP transistor has so far not
yielded a winning combination.

All suggestions would be appreciated please.

Terry, East Grinstead, UK

 

[Clive Arthur]

On 26/04/2019 09:49, Terry Pinnell wrote:

I have a couple of simple 555 monostables, the first to delay the
triggering of the second.
https://www.dropbox.com/s/6uboy3fgd0ixhxa/GenerateNegPulse-1.jpg?raw=1

But I'm struggling to extract the brief -ve pulse required for the Main
mono. I thought it would prove simple. But bread-boarding various
combinations of R, C, diode and NPN or PNP transistor has so far not
yielded a winning combination.

All suggestions would be appreciated please.

Terry, East Grinstead, UK

C on output going to R pulled up to supply. Possibly upwards pointing
diode across R, but doubt that's needed. CMOS 555s I guess?

Cheers
--
Clive

 

[Mike]

On 4/26/2019 1:49 AM, Terry Pinnell wrote:

I have a couple of simple 555 monostables, the first to delay the
triggering of the second.
https://www.dropbox.com/s/6uboy3fgd0ixhxa/GenerateNegPulse-1.jpg?raw=1

But I'm struggling to extract the brief -ve pulse required for the Main
mono. I thought it would prove simple. But bread-boarding various
combinations of R, C, diode and NPN or PNP transistor has so far not
yielded a winning combination.

All suggestions would be appreciated please.

Terry, East Grinstead, UK

A time axis might be helpful to know how critical the relative timing
might be...how fast do you have to reset the timing components?
How accurate/repeatable do the delay and pulse outputs have to be.
Are the delay and width fixed? Or vary over what range?

Have you tried an XOR gate with an RC on one input?

If you wanna have some fun, consider the emitter follower.
If you put a resistor in the base and drive current into the emitter,
the emitter impedance looks like the base resistor in parallel with an
inductor.
The time constant of that LR is the Tsub-t of the transistor. I'm too
sleepy
to remember, but it's something like 1/2pi*ft.
Works great as a fast differentiator.
The cool part is that the L was never really there, so when you
turn off the current, all you have to wait for is the charge in the
base junction to dissipate. The width of the pulse is relatively
independent
of the rep rate.

 

[Terry Pinnell]

Clive Arthur <cliveta@nowaytoday.co.uk> wrote:

On 26/04/2019 09:49, Terry Pinnell wrote:
I have a couple of simple 555 monostables, the first to delay the
triggering of the second.
https://www.dropbox.com/s/6uboy3fgd0ixhxa/GenerateNegPulse-1.jpg?raw=1

But I'm struggling to extract the brief -ve pulse required for the Main
mono. I thought it would prove simple. But bread-boarding various
combinations of R, C, diode and NPN or PNP transistor has so far not
yielded a winning combination.

All suggestions would be appreciated please.

Terry, East Grinstead, UK

C on output going to R pulled up to supply. Possibly upwards pointing
diode across R, but doubt that's needed. CMOS 555s I guess?

Cheers

Thanks Clive, appreciate that fast reply. Haven't bread-boarded it yet
but simulation looks good.
https://www.dropbox.com/s/dsnxzxm6pe4uo10/CreateNegEdge-1.png?raw=1

I rather think the diode is needed as I suspect the +ve pulse might
cause trouble?

Terry, East Grinstead, UK

 

[Terry Pinnell]

Mike <ham789@netscape.net> wrote:

On 4/26/2019 1:49 AM, Terry Pinnell wrote:
I have a couple of simple 555 monostables, the first to delay the
triggering of the second.
https://www.dropbox.com/s/6uboy3fgd0ixhxa/GenerateNegPulse-1.jpg?raw=1

But I'm struggling to extract the brief -ve pulse required for the Main
mono. I thought it would prove simple. But bread-boarding various
combinations of R, C, diode and NPN or PNP transistor has so far not
yielded a winning combination.

All suggestions would be appreciated please.

Terry, East Grinstead, UK

A time axis might be helpful to know how critical the relative timing
might be...how fast do you have to reset the timing components?
How accurate/repeatable do the delay and pulse outputs have to be.
Are the delay and width fixed? Or vary over what range?

Have you tried an XOR gate with an RC on one input?

If you wanna have some fun, consider the emitter follower.
If you put a resistor in the base and drive current into the emitter,
the emitter impedance looks like the base resistor in parallel with an
inductor.
The time constant of that LR is the Tsub-t of the transistor. I'm too
sleepy
to remember, but it's something like 1/2pi*ft.
Works great as a fast differentiator.
The cool part is that the L was never really there, so when you
turn off the current, all you have to wait for is the charge in the
base junction to dissipate. The width of the pulse is relatively
independent
of the rep rate.

Thanks Mike. I'll experiment with that later but Clive's ultra-simple
suggestion looks good!

Terry, East Grinstead, UK

 

[Terry Pinnell]

Mike <ham789@netscape.net> wrote:

On 4/26/2019 1:49 AM, Terry Pinnell wrote:
I have a couple of simple 555 monostables, the first to delay the
triggering of the second.
https://www.dropbox.com/s/6uboy3fgd0ixhxa/GenerateNegPulse-1.jpg?raw=1

But I'm struggling to extract the brief -ve pulse required for the Main
mono. I thought it would prove simple. But bread-boarding various
combinations of R, C, diode and NPN or PNP transistor has so far not
yielded a winning combination.

All suggestions would be appreciated please.

Terry, East Grinstead, UK

A time axis might be helpful to know how critical the relative timing
might be...how fast do you have to reset the timing components?
How accurate/repeatable do the delay and pulse outputs have to be.
Are the delay and width fixed? Or vary over what range?

Have you tried an XOR gate with an RC on one input?

If you wanna have some fun, consider the emitter follower.
If you put a resistor in the base and drive current into the emitter,
the emitter impedance looks like the base resistor in parallel with an
inductor.
The time constant of that LR is the Tsub-t of the transistor. I'm too
sleepy
to remember, but it's something like 1/2pi*ft.
Works great as a fast differentiator.
The cool part is that the L was never really there, so when you
turn off the current, all you have to wait for is the charge in the
base junction to dissipate. The width of the pulse is relatively
independent
of the rep rate.

Also meant to also reply to your questions about the time scale. Initial
delay mono trigger pulse not critical, but typically 100 ms. Delay mono
output user-settable between 1 and 30 s. Main mono user-settable between
5s and 7 mins. I've amended my illustration accordingly.

Nothing deserving much rigour, it's just hobby stuff. I'm using main
mono to light an external lamp as part of my project to get video of an
occasional overnight garden visit by a local fox and cub.

Terry, East Grinstead, UK

 

[Clive Arthur]

On 26/04/2019 11:39, Terry Pinnell wrote:

Clive Arthur <cliveta@nowaytoday.co.uk> wrote:

On 26/04/2019 09:49, Terry Pinnell wrote:
I have a couple of simple 555 monostables, the first to delay the
triggering of the second.
https://www.dropbox.com/s/6uboy3fgd0ixhxa/GenerateNegPulse-1.jpg?raw=1

But I'm struggling to extract the brief -ve pulse required for the Main
mono. I thought it would prove simple. But bread-boarding various
combinations of R, C, diode and NPN or PNP transistor has so far not
yielded a winning combination.

All suggestions would be appreciated please.

Terry, East Grinstead, UK

C on output going to R pulled up to supply. Possibly upwards pointing
diode across R, but doubt that's needed. CMOS 555s I guess?

Cheers

Thanks Clive, appreciate that fast reply. Haven't bread-boarded it yet
but simulation looks good.
https://www.dropbox.com/s/dsnxzxm6pe4uo10/CreateNegEdge-1.png?raw=1

I rather think the diode is needed as I suspect the +ve pulse might
cause trouble?

Terry, East Grinstead, UK

It's likely that the 555 input will have a protection diode, but I
haven't looked, that's just a guess, so yes, use one. A Schottky diode
would keep the pulse down to maybe 300mV above rail.

Cheers
--
Clive

 

[Phil Hobbs]

On 4/26/19 4:49 AM, Terry Pinnell wrote:

I have a couple of simple 555 monostables, the first to delay the
triggering of the second.
https://www.dropbox.com/s/6uboy3fgd0ixhxa/GenerateNegPulse-1.jpg?raw=1

But I'm struggling to extract the brief -ve pulse required for the Main
mono. I thought it would prove simple. But bread-boarding various
combinations of R, C, diode and NPN or PNP transistor has so far not
yielded a winning combination.

All suggestions would be appreciated please.

Terry, East Grinstead, UK

One method would be a couple of NAND gates and an RC, forming a "half
monostable".




0-*-------RRRR-------*-----------N
* | A___________0
| CCC N
| CCC *-----D
| | |
| GND |
| |
*------N |
| A-----------------*
| N
*------D

When the input is sitting high, the second NAND sees 10 so it stays high.

When the input goes low, initially the the second NAND sees 11, so its
output goes LOW. The RC charges up to the logic threshold, at which
point the second NAND sees 01 and brings its output high.

A Schmitt-trigger NAND such as a 74HC132 or 4093 would be best.

An RC and an XOR will generate pulses on both edges of its input.

Cheers

Phil Hobbs




--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
https://hobbs-eo.com

 

[Terry Pinnell]

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

On 4/26/19 4:49 AM, Terry Pinnell wrote:
I have a couple of simple 555 monostables, the first to delay the
triggering of the second.
https://www.dropbox.com/s/6uboy3fgd0ixhxa/GenerateNegPulse-1.jpg?raw=1

But I'm struggling to extract the brief -ve pulse required for the Main
mono. I thought it would prove simple. But bread-boarding various
combinations of R, C, diode and NPN or PNP transistor has so far not
yielded a winning combination.

All suggestions would be appreciated please.

Terry, East Grinstead, UK


One method would be a couple of NAND gates and an RC, forming a "half
monostable".




0-*-------RRRR-------*-----------N
* | A___________0
| CCC N
| CCC *-----D
| | |
| GND |
| |
*------N |
| A-----------------*
| N
*------D

When the input is sitting high, the second NAND sees 10 so it stays high.

When the input goes low, initially the the second NAND sees 11, so its
output goes LOW. The RC charges up to the logic threshold, at which
point the second NAND sees 01 and brings its output high.

A Schmitt-trigger NAND such as a 74HC132 or 4093 would be best.

An RC and an XOR will generate pulses on both edges of its input.

Cheers

Thanks Phil, neat, I'll get around to trying it, but see my earlier
reply to Mike.

Terry, East Grinstead, UK

 

[Terry Pinnell]

Clive Arthur <cliveta@nowaytoday.co.uk> wrote:

On 26/04/2019 11:39, Terry Pinnell wrote:
Clive Arthur <cliveta@nowaytoday.co.uk> wrote:

On 26/04/2019 09:49, Terry Pinnell wrote:
I have a couple of simple 555 monostables, the first to delay the
triggering of the second.
https://www.dropbox.com/s/6uboy3fgd0ixhxa/GenerateNegPulse-1.jpg?raw=1

But I'm struggling to extract the brief -ve pulse required for the Main
mono. I thought it would prove simple. But bread-boarding various
combinations of R, C, diode and NPN or PNP transistor has so far not
yielded a winning combination.

All suggestions would be appreciated please.

Terry, East Grinstead, UK

C on output going to R pulled up to supply. Possibly upwards pointing
diode across R, but doubt that's needed. CMOS 555s I guess?

Cheers

Thanks Clive, appreciate that fast reply. Haven't bread-boarded it yet
but simulation looks good.
https://www.dropbox.com/s/dsnxzxm6pe4uo10/CreateNegEdge-1.png?raw=1

I rather think the diode is needed as I suspect the +ve pulse might
cause trouble?

Terry, East Grinstead, UK

It's likely that the 555 input will have a protection diode, but I
haven't looked, that's just a guess, so yes, use one. A Schottky diode
would keep the pulse down to maybe 300mV above rail.

Cheers

On similarly minimalist lines, I'll test if this also works in
practice.:
https://www.dropbox.com/s/xbzl8mp8w66yb9r/CreateNegEdge-3.jpg?raw=1

(BTW, this old batch of 555s are not CMOS.)

Terry, East Grinstead, UK

 

[Tom Del Rosso]

Terry Pinnell wrote:

I have a couple of simple 555 monostables, the first to delay the
triggering of the second.
https://www.dropbox.com/s/6uboy3fgd0ixhxa/GenerateNegPulse-1.jpg?raw=1

But I'm struggling to extract the brief -ve pulse required for the
Main mono. I thought it would prove simple. But bread-boarding various
combinations of R, C, diode and NPN or PNP transistor has so far not
yielded a winning combination.

All suggestions would be appreciated please.

A 555, as the second one-shot, needs a brief pulse. That means you need
3 monostables instead of 2.

The 2 halves of a 4538 would do this without needing to shorten the
pulse in the middle. It can be retriggerable or not simply by feeding
an output back to an input. (It has Q and /Q, and 2 inputs where 1 is
inverted and then they are ORed.)

I'm weird because I never liked the 555. It should have been 2 chips
better optimized for astable and monostable. There's enough demand for
2.

 

[Mike]

On 4/26/2019 3:59 AM, Terry Pinnell wrote:

Mike <ham789@netscape.net> wrote:

On 4/26/2019 1:49 AM, Terry Pinnell wrote:
I have a couple of simple 555 monostables, the first to delay the
triggering of the second.
https://www.dropbox.com/s/6uboy3fgd0ixhxa/GenerateNegPulse-1.jpg?raw=1

But I'm struggling to extract the brief -ve pulse required for the Main
mono. I thought it would prove simple. But bread-boarding various
combinations of R, C, diode and NPN or PNP transistor has so far not
yielded a winning combination.

All suggestions would be appreciated please.

Terry, East Grinstead, UK

A time axis might be helpful to know how critical the relative timing
might be...how fast do you have to reset the timing components?
How accurate/repeatable do the delay and pulse outputs have to be.
Are the delay and width fixed? Or vary over what range?

Have you tried an XOR gate with an RC on one input?

If you wanna have some fun, consider the emitter follower.
If you put a resistor in the base and drive current into the emitter,
the emitter impedance looks like the base resistor in parallel with an
inductor.
The time constant of that LR is the Tsub-t of the transistor. I'm too
sleepy
to remember, but it's something like 1/2pi*ft.
Works great as a fast differentiator.
The cool part is that the L was never really there, so when you
turn off the current, all you have to wait for is the charge in the
base junction to dissipate. The width of the pulse is relatively
independent
of the rep rate.

Also meant to also reply to your questions about the time scale. Initial
delay mono trigger pulse not critical, but typically 100 ms. Delay mono
output user-settable between 1 and 30 s. Main mono user-settable between
5s and 7 mins. I've amended my illustration accordingly.

7 minutes is a long time for a 555.
Save yourself a lot of grief by using a CPU.
These are dirt cheap and trivial to program with nothing more than
a usb port and free high level language program. Demo example programs
to do (almost) what you want are on the website.

https://www.ebay.com/itm/Digispark-Kickstarter-Micro-General-USB-Development-Board-Arduino-ATTINY85-TDCA/233204306774?hash=item364c0f5356:g:wT4AAOSwpvZaKlQz

More expensive if you want 'em quick.

Nothing deserving much rigour, it's just hobby stuff. I'm using main
mono to light an external lamp as part of my project to get video of an
occasional overnight garden visit by a local fox and cub.

Terry, East Grinstead, UK

 

On Friday, April 26, 2019 at 3:08:30 PM UTC-4, Mike wrote:

On 4/26/2019 3:59 AM, Terry Pinnell wrote:
Mike <ham789@netscape.net> wrote:

On 4/26/2019 1:49 AM, Terry Pinnell wrote:
I have a couple of simple 555 monostables, the first to delay the
triggering of the second.
https://www.dropbox.com/s/6uboy3fgd0ixhxa/GenerateNegPulse-1.jpg?raw=1

But I'm struggling to extract the brief -ve pulse required for the Main
mono. I thought it would prove simple. But bread-boarding various
combinations of R, C, diode and NPN or PNP transistor has so far not
yielded a winning combination.

All suggestions would be appreciated please.

Terry, East Grinstead, UK

A time axis might be helpful to know how critical the relative timing
might be...how fast do you have to reset the timing components?
How accurate/repeatable do the delay and pulse outputs have to be.
Are the delay and width fixed? Or vary over what range?

Have you tried an XOR gate with an RC on one input?

If you wanna have some fun, consider the emitter follower.
If you put a resistor in the base and drive current into the emitter,
the emitter impedance looks like the base resistor in parallel with an
inductor.
The time constant of that LR is the Tsub-t of the transistor. I'm too
sleepy
to remember, but it's something like 1/2pi*ft.
Works great as a fast differentiator.
The cool part is that the L was never really there, so when you
turn off the current, all you have to wait for is the charge in the
base junction to dissipate. The width of the pulse is relatively
independent
of the rep rate.

Also meant to also reply to your questions about the time scale. Initial
delay mono trigger pulse not critical, but typically 100 ms. Delay mono
output user-settable between 1 and 30 s. Main mono user-settable between
5s and 7 mins. I've amended my illustration accordingly.

7 minutes is a long time for a 555.
Save yourself a lot of grief by using a CPU.
These are dirt cheap and trivial to program with nothing more than
a usb port and free high level language program. Demo example programs
to do (almost) what you want are on the website.

https://www.ebay.com/itm/Digispark-Kickstarter-Micro-General-USB-Development-Board-Arduino-ATTINY85-TDCA/233204306774?hash=item364c0f5356:g:wT4AAOSwpvZaKlQz

More expensive if you want 'em quick.

+1

Aren't there also gadgets on ebay that do exactly this job? I guess they might have a relay on the output though, which may or may not be what you want.

--

Rick C.

- Get a 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

 

[Terry Pinnell]

"Tom Del Rosso" <fizzbintuesday@that-google-mail-domain.com> wrote:

Terry Pinnell wrote:
I have a couple of simple 555 monostables, the first to delay the
triggering of the second.
https://www.dropbox.com/s/6uboy3fgd0ixhxa/GenerateNegPulse-1.jpg?raw=1

But I'm struggling to extract the brief -ve pulse required for the
Main mono. I thought it would prove simple. But bread-boarding various
combinations of R, C, diode and NPN or PNP transistor has so far not
yielded a winning combination.

All suggestions would be appreciated please.

A 555, as the second one-shot, needs a brief pulse. That means you need
3 monostables instead of 2.

The 2 halves of a 4538 would do this without needing to shorten the
pulse in the middle. It can be retriggerable or not simply by feeding
an output back to an input. (It has Q and /Q, and 2 inputs where 1 is
inverted and then they are ORed.)

Thanks, but two extra monos seems a tad OTT? I was hesitating even about
my second mono. Hopefully Clive's simple RC-derived suggestion will do
the job when I get back to the workshop later this weekend.

I'm weird because I never liked the 555. It should have been 2 chips
better optimized for astable and monostable. There's enough demand for
2.

Great chip IMO; compact, versatile and a relatively unfussy trigger.
(Although I'd prefer +ve going.) And lots of hobbyist circuits to play
with ;-)

BTW, very little space inside the case for this add-on. The delay mono
is on a small rectangle of veroboard with just a few holes left.

Terry, East Grinstead, UK

 

[Terry Pinnell]

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

On 4/26/19 4:49 AM, Terry Pinnell wrote:
I have a couple of simple 555 monostables, the first to delay the
triggering of the second.
https://www.dropbox.com/s/6uboy3fgd0ixhxa/GenerateNegPulse-1.jpg?raw=1

But I'm struggling to extract the brief -ve pulse required for the Main
mono. I thought it would prove simple. But bread-boarding various
combinations of R, C, diode and NPN or PNP transistor has so far not
yielded a winning combination.

All suggestions would be appreciated please.

Terry, East Grinstead, UK


One method would be a couple of NAND gates and an RC, forming a "half
monostable".




0-*-------RRRR-------*-----------N
* | A___________0
| CCC N
| CCC *-----D
| | |
| GND |
| |
*------N |
| A-----------------*
| N
*------D

When the input is sitting high, the second NAND sees 10 so it stays high.

When the input goes low, initially the the second NAND sees 11, so its
output goes LOW. The RC charges up to the logic threshold, at which
point the second NAND sees 01 and brings its output high.

A Schmitt-trigger NAND such as a 74HC132 or 4093 would be best.

An RC and an XOR will generate pulses on both edges of its input.

Cheers

Phil Hobbs

Not yet breadboarded but its sim leaves little doubt that it would work
fine:
https://www.dropbox.com/s/2nmmjjj5nexzze6/CreateNegEdge-4093-PH.png?raw=1


Terry, East Grinstead, UK

 

[Tom Del Rosso]

Terry Pinnell wrote:

Thanks, but two extra monos seems a tad OTT? I was hesitating even
about my second mono. Hopefully Clive's simple RC-derived suggestion
will do the job when I get back to the workshop later this weekend.

In place of the 555s, not in addition to it!

Sure it's preferable to just add another RC when you've already built
it, but I was suggesting why I don't like to use the 555 in the first
place. Because the 4538 responds to the edge and only to the edge and
doesn't care how long the pulse lasts, it wouldn't need an extra RC to
shorten the middle pulse.

 

On Friday, April 26, 2019 at 4:49:12 AM UTC-4, Terry Pinnell wrote:

I have a couple of simple 555 monostables, the first to delay the
triggering of the second.
https://www.dropbox.com/s/6uboy3fgd0ixhxa/GenerateNegPulse-1.jpg?raw=1

But I'm struggling to extract the brief -ve pulse required for the Main
mono. I thought it would prove simple. But bread-boarding various
combinations of R, C, diode and NPN or PNP transistor has so far not
yielded a winning combination.

All suggestions would be appreciated please.

Terry, East Grinstead, UK

Is the delay mono to debounce the trigger for the main mono? You only need one mono. Put an RC delay on its trigger such that the trigger delay is well in excess of your bounce time.

 

>Is the delay mono to debounce the trigger for the main mono? You only need one mono. Put an RC delay on its trigger such that the trigger delay is well in excess of your bounce time.

No. See earlier posts.

Terry, East Grinstead, UK