On 14 Feb 2007 08:39:09 -0800, "Mike C" <
[email protected]> wrote:
JF: Correct, i need to "detect the occurrence of 10 or more pulses in
one second regardless of the pulse width and separation between
pulses", and the LED to "come back on automatically if it subsequently
rose to >= 10pps" .... so the only time the LED would be off if pps
<10.
Please seehttp://tiberian5.googlepages.com/homefor an example of
what the input is, and what the output should be.
Thanks alot for your time.
Vcc--------------------+--------+------+
| | |
+---+ | |
| | | |
[1M]<-+ | |
| |3 |
14+--------+ | 15+---+---+2 |
PULSE>---|CPO | +----|RC R B|--+
13|___ ___|12 | 1|_ |13
+-O|CP1 5-9|----|---O|A Q|--+
|15| | | +---+---+ |
+--|MR | [4.7µF]HC123|14 [1K2]
| +--------+ | | |A
| HC4017 | | [HLMP4700]
| | | |
GND>--+----------------+--------+------+
An HLMP4700 is a 2 mA high-efficiency red LED which you can drive
directly from the HC123's output.
If you cant get one, or any other low-current LED, or you'd rather
use a 20mA LED, do this:
Vcc--------------------+--------+------+------------+
| | | |
+---+ | | |
| | | | [120R]
[1M]<-+ | | |
| |3 | [LED]
14+--------+ | 15+---+---+2 | |
PULSE>---|CPO | +----|RC R B|--+ |
13|___ ___|12 | 1|_ |13 C
+-O|CP1 5-9|----|---O|A Q|---[1000R]---B 2N3904
|15| | | +---+---+ E
+--|MR | [4.7µF]HC123|14 |
| +--------+ | | |
| HC4017 | | |
| | | |
GND>--+----------------+--------+-------------------+
Also, you won't be using the other one-shot, so connect the unused
inputs (pins 9,10,and 11) to ground.
I haven't shown the power pins either, and +5V goes to pin 16 and
ground goes to pin 8 on both packages.
---
I just noticed on sed that you've multiposted this thread instead of
crossposting. It would be better if you crossposted, since that way
everybody gets to follow the thread and post to it without having to
jump back and forth from newsgroup to newsgroup.
I'm going to crosspost this one over to sed even though it'll repeat
here. (seb)
JH: Excellent suggestion. I truly appreciate all your help,
especially the schematic. I will be ordering the HC4017 to do the
trick.. hopefully it'll be here in a few days... in the meantime, i'm
trying to simulate in orcad pspice and cant find the an HC4017
equivalent in the library, what did you use to simulate (if
anything) ?
---
I didn't, but I think your library has a 4017 in it, no?
---
---
You're welcome but, unfortunately, the circuit doesn't work
properly.
Consider: What's supposed to happen is that the one-shot is set to
time out in one second if it doesn't get retriggered by the 5-9
signal from the counter, which goes high when the counter rolls over
from 9 to zero, and goes low when the counter counts to 5.
The plan was that as long as ten pulses enter the counter in less
than a second then the 5-9 signal would continually retrigger the
counter and keep the LED on. That part works.
But... Consider this:
What if, say, no pulses were coming into the counter at all? Well,
the one-shot might flash for a second, but then it go out and stay
out, which is good. But now, let's say pulses come in at the rate
of one per second. As soon as the 10th pulse comes in, the 5-9
signal will trigger the one shot and it'll come on for a second. So,
it seems that any rate less than 10 pulses per second will cause the
LED to flash instead of going out completely.
What needs to happen in the circuit is that if the one-shot times
out it starts an astable with a one second period which keeps
resetting the counter once every second until the 5-9 signal comes
out and starts the one-shot again.
The plan there is that if the 5-9 signal didn't go true before the
astable reset the counter it was because the pulses were too slow,
and resetting the counter will get rid of what the counter's
accumulated and start from zero once a second until the pulses speed
up enough so that the 5-9 signal can get out and trigger the
one-shot.
I see you're on Google groups, so you can't access
alt.binaries.schematics.electronic, so I'll email you a schematic
when I'm done as well as post one there for anyone who's interested.
BTW, what kind of accuracy are we talking here? 5-10% ?