pulse delay circuit

[Mark Kelepouris]

Hello to all,
I'm in need of a simple delay circuit for the positive edge of a pulse of 12
VDC.
I need to create a delayed version of about 20 uS and it must be realiable
and within a couple of uS tolerance.
I am planning to use the 74HC123 dual oneshot for the delay control but i'm
not sure how best to translate 12 volts down to 5 and back up to 12 again at
the output without any unrealiablities adding to the circuit.
I'm guessing two tranny's and four resistors would be a bare minimum, but
i'm not sure which transistors i need to use and how best to bias and supply
voltage/current to them for the desired results. (12>5Vdc..20uS
delay..5>12Vdc)
Can anyone offer advice on this?

Thanks,
Mark Kelepouris

 

[petrus bitbyter]

Hello to all,
I'm in need of a simple delay circuit for the positive edge of a pulse of
12 VDC.
I need to create a delayed version of about 20 uS and it must be realiable
and within a couple of uS tolerance.
I am planning to use the 74HC123 dual oneshot for the delay control but
i'm not sure how best to translate 12 volts down to 5 and back up to 12
again at the output without any unrealiablities adding to the circuit.
I'm guessing two tranny's and four resistors would be a bare minimum, but
i'm not sure which transistors i need to use and how best to bias and
supply voltage/current to them for the desired results. (12>5Vdc..20uS
delay..5>12Vdc)
Can anyone offer advice on this?

Thanks,
Mark Kelepouris

Mark,

Look for a CMOS dual monostable like the CD4098B. It handles voltages up to
20V, so 12V pulses (along with 12V power of course) will meet your
requirements as far as the voltage concernes. You'll need the datasheet as
the CD4098B is functionally compatible, but the pinout and the timing
differ.

petrus bitbyter

 

[Mark Kelepouris]

Mark,

Look for a CMOS dual monostable like the CD4098B. It handles voltages up
to 20V, so 12V pulses (along with 12V power of course) will meet your
requirements as far as the voltage concernes. You'll need the datasheet as
the CD4098B is functionally compatible, but the pinout and the timing
differ.

petrus bitbyter

Thanks petrus,
I was kind of hoping there'd be a simpler solution, looking forward to
getting hold of that chip.
It seems unusually unlucky for me, that my 'Howard W. Sams & Company' cmos
cookbook i have, has the 4097 as the last entry. After that, the 45xx come
into play.

 

[Fred Bloggs]

I'm in need of a simple delay circuit for the positive edge of a pulse of 12
VDC.
I need to create a delayed version of about 20 uS and it must be realiable
and within a couple of uS tolerance.
I am planning to use the 74HC123 dual oneshot for the delay control but i'm
not sure how best to translate 12 volts down to 5 and back up to 12 again at
the output without any unrealiablities adding to the circuit.
I'm guessing two tranny's and four resistors would be a bare minimum, but
i'm not sure which transistors i need to use and how best to bias and supply
voltage/current to them for the desired results. (12>5Vdc..20uS
delay..5>12Vdc)
Can anyone offer advice on this?

View in a fixed-width font such as Courier.

 

[T. Atkin]

To convert down the 12V input pulse, you just need a small resistor say 10K
between the pulse source and the input of the 74HC123 chip. The input diode
protection of the 74HC123 will clamp the voltage down.
To reconvert the output of the monostable to 12V, you can use a transistor
like 2N3904. A pullup resistor of 4k7 should be ok to keep the output rising
edge sharp enough.

Tom

 

[John Fields]

Hello to all,
I'm in need of a simple delay circuit for the positive edge of a pulse of 12
VDC.

 

[Joerg]

Hello Mark,

Thanks petrus,
I was kind of hoping there'd be a simpler solution, looking forward to
getting hold of that chip.
It seems unusually unlucky for me, that my 'Howard W. Sams & Company' cmos
cookbook i have, has the 4097 as the last entry. After that, the 45xx come
into play.

The 4098 costs 48 cents in single qties at Digikey. The 4528 used to be
popular but Digikey carries no stock. Then there is the 4538, in stock,
but a few cents more.

Simpler solution? You could build something with two sections of a
CD40106 but it won't be much simpler. RC delay with another resistor
plus diode across the R if you want different delays for rising and
falling edges. But now you'd rely in part on the threshold values for
timing.

 

[Tim Williams]

Discrete solution. With better R values the R-S f/f can be two transistor.
Add another if you want a pulse after a delay rater than just a delay.

http://webpages.charter.net/dawill/Images/One-shot Timer.gif

Timing should be consistent enough (with respect to R and C) without
adjustments (as opposed to, say, CMOS threshold variation).

Tim

 

[Mark Kelepouris]

The pos. edge of my input pulse will trigger the first oneshot (which is
fine tunable to give the desired delay) The neg. edge of this pulse will
trigger the second oneshot, which will provide the 'new' delayed pulse.
As you probably know, the 74HC123 can be configured to trigger on neg. or
pos. edges. So the only problem is the voltage translation.

Mark

 

[petrus bitbyter]

Thanks petrus,
I was kind of hoping there'd be a simpler solution, looking forward to
getting hold of that chip.
It seems unusually unlucky for me, that my 'Howard W. Sams & Company'
cmos cookbook i have, has the 4097 as the last entry. After that, the 45xx
come into play.

The datasheet can be found on the net easily. Google for "CD4098B
datasheet". (Without the quotes of course). Farnell and Digikey sells them
for about half a dollar. If you can't find the datasheet, I can sent you
one.

If component count and space are not an issue, you can keep the 74HC123. See
Fred Bloggs schematic. You will have to make a 5V supply (an 7805 and some
capacitors). Also keep in mind that the simple transistor amplifier is not
intended for very high speed.

petrus bitbyter

 

[John Fields]

Thanks petrus,
I was kind of hoping there'd be a simpler solution, looking forward to
getting hold of that chip.
It seems unusually unlucky for me, that my 'Howard W. Sams & Company' cmos
cookbook i have, has the 4097 as the last entry. After that, the 45xx come
into play.

---
The 4538 will also work, but if you're looking for utter simplicity,
why not try this, (View in Courier)


| \ | \
IN>---[POT]<--+---| >O---O| >-->OUT
| | / | /
[C]
|
GND>----------+

where the inverters are 1/3 of a 40106?

 

[John Fields]

The pos. edge of my input pulse will trigger the first oneshot (which is
fine tunable to give the desired delay) The neg. edge of this pulse will
trigger the second oneshot, which will provide the 'new' delayed pulse.
As you probably know, the 74HC123 can be configured to trigger on neg. or
pos. edges. So the only problem is the voltage translation.

 

[Mark Kelepouris]

---
I understand, but my question was whether you were concerned with
the location of the trailing edge of the delayed pulse. Since
you'll be using two one-shots, however, you can make it fall
wherever you want.

Hi John,
The 4538 worked to the book. I have it up and running. The trailing edge of
the final pulse doesn't matter much, as long as the pulse is kept short. The
only trailing edge that does of course, is in the delay section.
Mark Kelepouris