simple one-shot pulse detector circuit needed

etector out of two of transistors and a few resistors, but I can't find the circuit anywhere. Searches keep throwing up stuff about astable multivibra tors and nand gates and that's not what I'm looking for.

line. The pulse comes only after several days of inactivity and should turn an LED on permanently. No reset required and any subsequent pulses must *n ot* turn the LED off again, so it's operating like a bistable latch (if tha t's the right term).

I assume there is another power line to run it from (+5 V). I don't know the transistor circuit, but how about a S/R flip flop?

George H.

On Tue, 20 Nov 2012 05:15:02 -0800 (PST), snipped-for-privacy@virgin.net wrote:

detector out of two of transistors and a few resistors, but I can't find the circuit anywhere. Searches keep throwing up stuff about astable multivibrators and nand gates and that's not what I'm looking for.

The pulse comes only after several days of inactivity and should turn an LED on permanently. No reset required and any subsequent pulses must *not* turn the LED off again, so it's operating like a bistable latch (if that's the right term).

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-- JF

An SCR would do it, once triggered it only turns off if it loses power on the anode.

You can get the effect of an SCR with two transistors, at least for this purpose. I can't remember, but doing a search for something like that should do it.

Michael

detector out of two of transistors and a few resistors, but I can't find the circuit anywhere. Searches keep throwing up stuff about astable multivibrators and nand gates and that's not what I'm looking for.

The pulse comes only after several days of inactivity and should turn an LED on permanently. No reset required and any subsequent pulses must *not* turn the LED off again, so it's operating like a bistable latch (if that's the right term).

Now make it blink miser-style, as in LM3909 ;-)

Message-ID:

...Jim Thompson

detector out of two of transistors and a few resistors, but I can't find th e circuit anywhere. Searches keep throwing up stuff about astable multivibr ators and nand gates and that's not what I'm looking for.

line. The pulse comes only after several days of inactivity and should tur n an LED on permanently. No reset required and any subsequent pulses must * not* turn the LED off again, so it's operating like a bistable latch (if th at's the right term).

Nice... but I had to reduce C1 from 47 Farads to 47nF :^)

George H.

detector out of two of transistors and a few resistors, but I can't find the circuit anywhere. Searches keep throwing up stuff about astable multivibrators and nand gates and that's not what I'm looking for.

line. The pulse comes only after several days of inactivity and should turn an LED on permanently. No reset required and any subsequent pulses must *not* turn the LED off again, so it's operating like a bistable latch (if that's the right term).

Along these lines, what would the group recommend for a weatherproof switch to detect that a yard gate is not closed all the way? ...Jim Thompson

detector out of two of transistors and a few resistors, but I can't find the circuit anywhere. Searches keep throwing up stuff about astable multivibrators and nand gates and that's not what I'm looking for.

line. The pulse comes only after several days of inactivity and should turn an LED on permanently. No reset required and any subsequent pulses must *not* turn the LED off again, so it's operating like a bistable latch (if that's the right term).

The 1 second requirement significantly complicates the solution. If any old pulse will do, use a latching relay...either magnetic latch or feedback from the contacts.

As always, the devil is in the details. How much current can you get out of the 5V pulse? What voltages are available when the pulse is not present? How do you expect to reset the thing? What are the specific details of the 1 second requirement? Timing accuracy and boundary conditions? Assume you wouldn't have mentioned it if it weren't important.

magnet/reed switch from a burglar alarm door/window ajar sensor.

detector out of two of transistors and a few resistors, but I can't find the circuit anywhere. Searches keep throwing up stuff about astable multivibrators and nand gates and that's not what I'm looking for.

line. The pulse comes only after several days of inactivity and should turn an LED on permanently. No reset required and any subsequent pulses must *not* turn the LED off again, so it's operating like a bistable latch (if that's the right term).

.. or just a resistor (eg. 4K7) to drive the gate of a 2N5064, in turn drive an LED with series resistor (4 parts). It will detect a positive pulse of any length greater than a couple microseconds by latching on, and thence cease to care about the state of the input, so the LED will stay on until the power is cycled.

Should be battery powered sensors with RF interface available for security.

Outdoors? It wouldn't last. Depending on the type of latch, one of several types of industrial position sensor would be the best bet.

I missed that part of the specification. Probably want three or more magnetic sensors physically placed and logically connected to insure that it can't be spoofed by a magnet without intimate knowledge of the design. Encase the bullet-resistant box in concrete. Probably want to put a signal into the razor wire so you can use it as a proximity sensor. Maybe a satellite phone to call the cops when the phone lines get cut. And a bluetooth connection to the alarm system with an encrypted heartbeat so it can't be jammed. Probably want at least one guard dog with a wireless heart rate sensor just in case they get put to sleep. Of course, destroy all documentation and eliminate everybody you ever discussed it with. Crush the hard drive. Grind it up into dust and scatter it at least 10 miles off shore.

If security isn't the primary requirement, there are lots of devices. The Powerhouse MS13A is a X-10 wireless PIR motion detector. You could hack a relay into that and get motion plus gate detection. They have other alarm sensors, but I don't know the numbers. There are devices designed to alert you when your mailbox door is opened. Driveway occupancy sensors. Wireless doorbells. Garage door openers. RF TV remotes.

And my personal favorite...close the damn gate. ;-)

And the gate is steel. Maybe the other way around, a coil whose inductance changes with gate position? ...Jim Thompson

-- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

Some of us, often referred to as the "evil rich", EMPLOY paisanos who fail to close the gate.

I know what to do... fire 'em all ;-) ...Jim Thompson

Replace them with an electric gate closer. I still see lots of those

The two eight foot pieces of 6" black iron pipe cost me a lot more than that. The old gate posts are wood, and the gates change position,, depending on the amount of rain.

There are waterproof inductive proximity sensors with all the circuitry in a little tube.

Jim said 'yard gate' and a motor is more suited for a driveway gate.

For the sensor I'd say light beam interruption over a 1-inch gap into which a little tab enters.

To close it automatically the hinge can be easily modified to use gravity, with a magnet to pull it the last centimeter hard enough to engage a latch.

Just put a shim between the upper hinge and the post, and mortise it more deeply into the gate. The magnet might not be needed.

Can't get this to run for some reason, John. This is a LT spice netlist? Just get the following error message: "multiple instances of SYMATTR" Since someone else on this thread seems to have got it going (albeit with a slight mod to a cap value) I assume I'm doing something wrong (not an unknown experience).

Yes, I'm aware a SCR would be ideal, but I only have great fat thumping big ones lying around which would be a waste for such a small signal application.

Malvino's book Electronic Principles shows the kind of thing I'm talking about, I've just discovered, at page 501. Vanishingly terse explanation with no reference to it in the index or contents for some reason. Uses a BJT PNP/NPN pair with bases and collectors shorted together between them and one resistor in the Vcc line. I reckon this should do the trick with any luck.

Here's the netlist of the Malvino design. Seems to run alright...

"ExpressPCB Netlist" "LTspice IV Version 4.17"

"Net Names Table" "N003" 1 "N004" 3 "0" 6 "N002" 9 "N001" 11

"Net Connections Table"

Hmm, I just cut and pasted the whole thing into notepad... or pick some other text editor. Then save it with a .asc ending, into my ltspice/bin and run it.

George H.