Hi all.

This is my first question on your forum. I'm just wondering how will I generate a high signal for 1.5seconds from a short 50mS hi pulse?????

Jason

 

You can use a 555 timer monostable circuit. It's like a single pulse generator. Every time you send a pulse to the input, it generates another pulse that remains high for a certain amount of time. You can Google for the circuit- it's one of the two basic 555 timer circuits.

 

Sorry, I should of said; I didn't want to use a 555 timer (already thought of this) due to cost, I'm gonna be building 50 - 75 of these so I wanted to keep cost to a minimum. I was just wondering is there any cheap and nasty options??

Jason

 

Build a discrete monostable instead - but it's slightly more complicated, two transistors, five resistors and a capacitor (off the top of my head!).

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I'll search on the internet now, could you have a look (if you have the time) and give me a point in the direction

Jason

 

You can do it with a Hex Schmitt Trigger such as the 40106, 74HC14, etc.

You need 2 resistors, one diode and one capacitor per Schmitt.

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Len

 

Here is one way to do it. It is designed for a 10:1 ratio.

You can change the 100k to give you a different ratio.

Change the capacitor for longer or shorter times.

Attached Images

Pulse stretcher.gif (4.1 KB, 62 views)

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Len

 

I'm looking at 74HC14, but could you explain more, it looks like this wouldn't work??

Jason

 

plus the signal is reversed

 

I just posted a circuit. It does work, I've used it many times.

For example, I used it in a garage door opener. I wanted to make the light stay on for about 2 minutes.

So the delay is started when the up or down button is pressed and remains on for approx 2 min.

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Len

 

Use another inverter to invert the output.

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Len

 

Could you tell me where the cct is, Is it very expensive to make, don't for get I'm making 50 of these?

Jason

 

The circuit is 5 posts above.

You could also use the same technique with 556 ICs, but there are only 2 per IC so it is probably more expensive.

Do you have to have a positive trigger and a positive output?

If not, then you obtain 6 circuits per 40106.

Alternatively, as someone wrote, you could use a dual Monostable.

Then you only need one R and one C.

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Len

 

I'm using a PIC to send a pulse and I want this cct I'm trying to get to switch a transistor for approx 1.5 seconds.

I got a positive input and I need a positive output.

I've looked at the dual Monostable on the internet and can't find an example to look and see how it works and re-construct on Multisim??

Jason

 

Look at the data sheet of the Mono.

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Len