Veritas, you mentioned having the 555 in astable mode. Shouldn't it be in monostable to generate just 1 pulse?

Yes, I misspoke (sniper fire), and meant monostable.

 

Thanks for the help. I am going to try two setups tomorrow, the 555 into the instantaneous pulse curcuit provided, and using 2 555's, and see which one works best.

One more question. I need to trigger the first 555 on a positive input pulse, about 3.5V. Since the 555 is triggered on the falling edge, I was thinking of using my input pulse as a control line to a transmission gate, and have the input of the gate tied to ground. So once the gate is opened, ground will be directly tied to the trigger pin. Will it need a pull down resistor to shut the gate once my input pulse returns to 0? This is assuming the trigger pin is pulled high. Is this the only way to configure a monostable circuit (Since triggering is accomplished when trigger pin is taken from high to below 1/3V+)? Is there any way to have this pin floating or tied to ground, then have it triggered when the input pulse is sent driving pin 2 high? This is howmy circuit will be.

Second I was thinking about using the reset pin somehow since it is activated by a positive voltage and only needs less than a volt. I know someone posted about using this reset earlier but I don't quite get how it can be used. Do either of these two suggestions sound feasible? Which one is recommended? Thanks!

 

Can you pass your trigger input through an inverter? Would that do the trick?

 

robby991,

My dual 555 monostables dealt with the positive going leading edge of your analog signal with the 2N3904 as an inverter. Not knowing what the characteristics of your "transmission gate" (part #...?) are, it might be possible to use it directly in place of the 2N3904.

With the continued discussion...are you looking at reducing the total part count for practical purposes, or just intrigued with the possibilities?

Ken

 

Ken, just looking at different ways it can be done. Also, does anyone know how this circuit can be implemented using a crystal oscillator? I want to try it but I never used an oscillator before. Any thoughts? Is this possible?

 

robby991,

Where are you thinking of using a "crystal oscillator" in your delay circuit? Are you thinking of using it to time the delay, and output gating period?

Ken

 

Ken. Yes i am thinking to use it for timing a 1s delay. Is this possible?

 

Ken. Yes i am thinking to use it for timing a 1s delay. Is this possible?

Do you mean [1mS] delay, as in your original post? Is the accuracy of this time period critical? It will add a more circuitry.

Ken

 

If you want a pretty accurate 1Hz signal, you could use a CMOS MC14060B (4060, 14-Bit Binary Counter and Oscillator) with a 32768Hz crystal and support components.
Link to datasheet:
http://www.onsemi.com/pub/Collateral/MC14060-D.PDF

Xtal oscillator connections described on page 5.

 

Yes I ment 1ms. I would like to know to vary this delay also.

 

robby991,

Since you're looking at crystal/digital, changes are then in discrete steps rather than in infinately (relatively) small changes. But, maybe more stable. What's the smallest step (0.1mS, 0.05mS, 0.01mS...?) that you want to be able to increase or decrease your 1mS delay?

Ken