a similiar question has been asked before however the thread was very long.
i want to use a kitchen timer 1.5v, with piezo buzzer to turn on an scr (2n5064 ?) to power something at 9v.

if someone could draw the schematic for a simple circuit i would be grateful.
i can make up circuits like lego but my actual knowledge of how they work is limited.

conecting the scr to the piezo buzzer does not work.

thank you
dave

 

Why an SCR?

 

Why an SCR?

As Dave said, his understanding of electronics is limited. It could be that somewhere he's heard that an SCR can be used as a switch. But with limited understanding of how an SCR works he may not know that once turned on with a DC source it will keep itself on until power is removed. Dave: An SCR is the wrong choice.

I would guess that an Opto-Isolator would work better in this situation. However, not knowing how the piezo interacts with the timer an Opto might not be the best choice. The way an Opto works - it has an LED inside that shines its light on a photo transistor. When the light strikes the base of that transistor it conducts. Whatever voltage is present - provided you don't exceed its specs - will turn on a device that a 9V source runs on.

I used to have a bunch of components pre-drawn so I could grab something and bang out a drawing. I can do something in Paintbrush and post it, but it will take a bit. Paintbrush isn't the best for drawing electronic circuitry. AND off hand I don't know which components to choose for best results, so I won't be specifying any particular devices.

 

When you say " piezo buzzer " do you mean just the transducer or an item which includes a driver for the transducer ?
If it is just the transducer the signal is an AC signal of quite a high voltage but a very low current . If this is the case it will probably not provide enough current to trigger an SCR.

Les.

 

When you say " piezo buzzer " do you mean just the transducer or an item which includes a driver for the transducer ?
If it is just the transducer the signal is an AC signal of quite a high voltage but a very low current . If this is the case it will probably not provide enough current to trigger an SCR.

That's an important question.

Nevertheless, here's a diagram banged out just to show concept. R Load is whatever it is you're powering through a 9V battery. You didn't say it was a battery but I'll just assume it's a 9V battery. The opto turns on when the buzzer is powered. As @LesJones said, it depends on the exact functioning of the buzzer. If it's a simple 1.5V source you'll need to find an opto that can run on that low a voltage. I am not extensively experienced with Opto's so someone else may fill in the missing details. But assuming it's a simple 1.5V DC source then the circuit below might fit your requirements.


The timer I have on my bench is AC driven. It has a COB (Chip On Board) that signals a transistor that switches an inductor on and off producing an ac source connected to the piezo. It's not a simple DC circuit and would not work in the case of what I've drawn. It might but you'd need an additional diode to block high voltage reverse currents otherwise you'll blow out the Opto.

 

Why an SCR?

i thought it wopuld be the simplest solutio. i have limited knowledge in electronics.

 

As Dave said, his understanding of electronics is limited. It could be that somewhere he's heard that an SCR can be used as a switch. But with limited understanding of how an SCR works he may not know that once turned on with a DC source it will keep itself on until power is removed. Dave: An SCR is the wrong choice.

I would guess that an Opto-Isolator would work better in this situation. However, not knowing how the piezo interacts with the timer an Opto might not be the best choice. The way an Opto works - it has an LED inside that shines its light on a photo transistor. When the light strikes the base of that transistor it conducts. Whatever voltage is present - provided you don't exceed its specs - will turn on a device that a 9V source runs on.

I used to have a bunch of components pre-drawn so I could grab something and bang out a drawing. I can do something in Paintbrush and post it, but it will take a bit. Paintbrush isn't the best for drawing electronic circuitry. AND off hand I don't know which components to choose for best results, so I won't be specifying any particular devices.

yes , it doesnt matter the power stays on once the scr is triggered

 

When you say " piezo buzzer " do you mean just the transducer or an item which includes a driver for the transducer ?
If it is just the transducer the signal is an AC signal of quite a high voltage but a very low current . If this is the case it will probably not provide enough current to trigger an SCR.

Les.

the piezo presumably has its own driver in the kitchen timer (1.5v)

 

How would you shut it off? You'd have to put a momentary open switch in line with the SCR's power source otherwise you'll drain your battery.

I edited my previous comment, so you might want to look back at it just to make sure you have all I said.

As I said, I have a timer on my bench that produces an AC signal. A piezo by itself doesn't work on DC. It takes circuitry.

 

That's an important question.

Nevertheless, here's a diagram banged out just to show concept. R Load is whatever it is you're powering through a 9V battery. You didn't say it was a battery but I'll just assume it's a 9V battery. The opto turns on when the buzzer is powered. As @LesJones said, it depends on the exact functioning of the buzzer. If it's a simple 1.5V source you'll need to find an opto that can run on that low a voltage. I am not extensively experienced with Opto's so someone else may fill in the missing details. But assuming it's a simple 1.5V DC source then the circuit below might fit your requirements.
View attachment 265931

The timer I have on my bench is AC driven. It has a COB (Chip On Board) that signals a transistor that switches an inductor on and off producing an ac source connected to the piezo. It's not a simple DC circuit and would not work in the case of what I've drawn. It might but you'd need an additional diode to block high voltage reverse currents otherwise you'll blow out the Opto.

as you say, i dont think there is 1.5v at the piezo so i dont think that would turn the opto isolator on, there is 0.1v across the piezo when its beeping.

 

How would you shut it off? You'd have to put a momentary open switch in line with the SCR's power source otherwise you'll drain your battery.

I edited my previous comment, so you might want to look back at it just to make sure you have all I said.

As I said, I have a timer on my bench that produces an AC signal. A piezo by itself doesn't work on DC. It takes circuitry.

once the scr latched turning it of would not be a problem for me.

could the piezo buzzer trigger a 555 as a one shot ?

 

Let‘s take a step back for the moment. Forget the kitchen timer and the SCR.

You have a device powered by a 9V battery. What is this device?
You want the device to be activated after a preset delay.
How long must the device be turned on?
How will the device be turned off?

 

Let‘s take a step back for the moment. Forget the kitchen timer and the SCR.

You have a device powered by a 9V battery. What is this device?
You want the device to be activated after a preset delay.
How long must the device be turned on?
How will the device be turned off?

the device only needs to be turned on.
it will be on for as long as i like and until i turn it off.
it doesnt have to use an scr maybe a relay would be more suitable and give more scope for what it could be used for.
(turning things on after a set time)

 

maybe a mosfet would be better than an scr.
maybe a 2n700 ?

 

Is the device to be turned on at a set time of the day and turned on only once?
Or is the device to be turned on every day at the same time?
Or is the device to be turned on once after a time delay after the timer has been started?

 

I think the device - whatever that may be - is turned on by this "System". It stays on until a user interfaces with it to shut it off. May be a minute, maybe an hour, maybe a week. IF the piezo is powered by an alternating signal (likely it is) it can be rectified and filtered. It's quite possible there will be enough power to flash on an Opto. Just make sure you know how high the voltage is going once rectified.

IF the voltage is actually 0.1V then that won't turn on any mosfet's. Nor will it turn on an opto. Until we know more about the timer we're just poking our finger into a fog bank hoping to find a telephone. Then - who do we call ? ? ?

 

this is the timer clock, 1.5v
https://www.ebay.co.uk/itm/185145893447?_trkparms=ispr=1&hash=item2b1b8e2247:g:B1QAAOSwblth-~MY&amdata=enc:AQAGAAAA4Lecz926qxdrslpA5ptNJX+qX2ZPsP0xqV04priETIzecNRaDCPDJDQG3zJ1iKEUU/rJwc6ZYHhdeJqbT38oiC6SUAvU8FRq/UzxAdru6ResFD8N+RsoQomMRLIVu84WxypugvAUgJ2HUzNcH9mwWkD6eOLGQV+glhlybGKQLGKEbIG4ElNCZOX0bVGJ8UtjhUQRK0Ue2gMP1faK0wVLBxJymLGXT8CZDmMYMGC48dEbPDVymoA2ng4+AY/UYX7ubdgk5I1qpsk209jboEiVtgEM36wxLNhyDC1+BDma2lXi|tkp:BFBMzrm2z41g

how would you rectify the signal from the piezo ?

 

A piezo is basically a speaker. Well, nothing like a speaker. But it flexes back and forth as you change the direction of the charge. Its size dictates at what frequency it vibrates the greatest. Hence, it's an AC device. You can either full wave rectify it using Schottky diodes or you can use a single diode and just ignore half of the wave cycle. Then after rectifying the current you put a filter cap to bring up the charge level. Same way you do with a regulator.

Now, I'm assuming that the driving circuit for the piezo isn't dependent on some sort of feedback from the piezo.

 

By the way; this is your link.
https://www.ebay.co.uk/itm/185145893447
Notice I've removed everything from the question mark on. That's used for tracking and none of us care to be tracked. In the future, if you copy and paste a link you can edit it to remove everything from the question mark on to the end.

 

I think he just wants to time the operation a 9 Volt device (or maybe higher) using a kitchen timer.