piezo sensor connection

[goodpickles]

How do I connect a piezo sensor to a 555 timer? do I need to use a transistor, I won't I be able to find one with a high enough gain?

 

[Juglenaut]

A 555 timer can drive a piezo if the load is sufficient.

There is a propagation delay for the piezo to actually make sound.

If a trasistor is needed just use a 1N4007 NPN general. Drive the base with 2 resistors to divide voltage. Since the voltage output of a 555 is realitivly high drop in a inline resistor to drop the signal output of the 555.

Use 2 100kohm to divide the VCC equally into the base, this does not require coupling, but pay attention to divider current if it is to high it can fry the 555, I would work the voltage and resistances to equal .75 volts base to emmiter junction voltage, just bearly enough to activate the transistor, and be under 50uA of current and the input to the trasistor form the 555 to equal about double or 100uA or more. Yes I am getting at a common collector transistor set-up, using it that way will make sure you get enough current at a given voltage to drive the piezo.


On the other hand I still trying to figure out what you are try to do exactly.

 

[TheOne]

How do I connect a piezo sensor to a 555 timer? do I need to use a transistor, I won't I be able to find one with a high enough gain?

What piezo? Where do you want to connect it? Input or output. If you want help you must be more to the point.

 

[goodpickles]

excuse me for not making it plainer...it should be input. I will be using a piezo film shock sensor.

 

[jbeng]

I assume you're wanting to connect it to a 555 one-shot circuit to get a reasonably precise pulse width output? Here's another post which shows a little circuit I've used before:https://www.electro-tech-online.com/threads/tank.13220/
You should be able to connect the output of the LM311 directly to the input pin (pin 2) of the 555 one-shot. Keep in mind that when it's hooked up like this (direct-coupled), the output pulse from the 555 will only be as narrow as the input pulse (making the assumption that the input pulse is wider than your 555's time constant). To change this, put a capacitor (0.01uF) in series with the trigger pulse from the LM311 and use a pull-up resistor (4.7Kohms) connected from the 555's pin 2 to pin 8 (or change your 555's time constant and therefore output pulse width).
Hope this helps you ... It worked well for me, your mileage may vary.
JB

 

[TheOne]

Remember if you use the 311 as a comparator, make sure you read the application hints. This is a fast comparator and you can run into all sorts of problems (multiple switchings, oscillations etc.) if you don't pay attention to certain things. Most of the time users don't even know that they have multiple switching on the output without looking on a very fast analog scope or digital storage scope.

https://www.electro-tech-online.com/custompdfs/2004/12/LM111.pdf

 

[jbeng]

Remember if you use the 311 as a comparator, make sure you read the application hints.

Good point. It's always a good idea to see what the designers of the chip suggest.
After all, who knows the chip better than they do?
JB
ps - The One, who's that pictured in your avatar?

 

[TheOne]

ps - The One, who's that pictured in your avatar?

https://www.electro-tech-online.com/threads/ac-vs-dc-breakers.13075/#post-69618