How to design a simplest trigger circuit

A new circuit might use a XOR gates.

D from BC

How about an AND gate ?

Rene

Think carefully about how a switch works. It generates a square pulse, 'low' when the switch is off, 'high' when its on. Controls a light perfectly. Just make sure your switch carries enough current to drive the light.

Let me clarify little more about the logic I want to implement. The light source we have works on TTL logic thus we need one pulse for "TURN ON" he lamp and the next pulse for "TURN OFF". Using AND and XOR gates will not solve my problem. As I have only one square pulse and we have to use this for generating trigger pulses. Thus in principle we need two pulses one TTL pulse at rising edge and one at falling edge. I will appreciate your comments.

Sure they will. An XOR with one input high acts as an inverter, so the other input can be tied to the AND's output. Voila, NAND gate. Now you can make *any* complete digital circuit.

Hint: sequential logic. You want a type T flip-flop.

Tim

-- Deep Fryer: A very philosophical monk. Website @

Yes, most likely implemented with Qbar tied back to D on a D-ff Of course, this is a crappy control scheme since you can easily get out of sync. Now if someone observes the light, then there isn't an issue.

This certainly goes to show you that phrasing the question correctly is half the battle. I had worked with a guy that went to some seminar where he learned that you should ask same question three times in slightly different manners to be sure you are getting the right answer. It drove me nuts. For the longest time I answered twice, then on the third pass I stated I answered the question twice already. Eventually I learned about the stupid seminar "trick:" he learned. I suppose with some people the three times is the charm technique is required.

On a sunny day (Wed, 21 Nov 2007 14:34:05 -0800 (PST)) it happened snipped-for-privacy@sushi.com wrote in :

Some years ago I flew to Miami from Amsterdam, and they have these interviews now, before you check in, to see if you are a potential terrorist or something. Now I had zero hours sleep the night before (lots of travelling), so I was sort of short tempered. After the security guy asked me 3 times the same question 'if I thought somebody put a bomb in my luggage', I asked him for my money back. That really worked, some other more normal guy took over, looked at me, and let me pass.

Is this it?

--------+ +-----------

--------+ +----------+ +--------

|triggers light to toggle |triggers light to toggle

(Now where have I seen this before??? :)

If so...there could be an XOR gate in the circuit..

D from BC

you need to use a Flip flip or flip flop relay..

Yes I want to implement this

------+ +-----------

OUT +--+ +---+ | | | | | | | | ------+ +--------+ +--------

See John Fields post.. It's the XOR&RC portion of the circuit that you're looking for..

I guess one way of understanding the XOR/RC circuit is like this: The XOR is a phase comparator and the RC makes lag. The XOR only stays high only while the RC is still catching up with the new state. Or..In other words... The XOR stays high for as long as there is an indifference between the signal and the RC.

D from BC

yes i get his Jhon's Idea, its wonderful :) thx

I'm sorry, but this takes two ICs. RC determines the output pulse length. Use 74HC logic, 74hc04 and 74hc00 parts. You must have crisp edges without slow risetimes, or bounce, etc. ___ ___ ____ o----+---- INV ----------| \\o------, |________| in | ,-----|___/ NAND | _ _ +-- R --+-----+ | ___ __| |______| |___ | C | '---o| \\_______ out | | INV ,---o|___/ NAND | GND | ___ | | '-----| \\O------' '-------------------|___/ NAND

Actually, he needs the dflop also in order to eliminate the ambiguity about whether the pulse was generated by the leading or trailing edge of the input signal.

On Wed, 21 Nov 2007 17:41:00 -0800, D from BC wrote: [snip]

That function already exists in my "AlternatingEdge" circuit I did for you... it's the trigger "blanking".

...Jim Thompson