Hi, I've just started learning electronics and found AAC which has been a really great resource for studying so I decided to join the forum. I have some knowledge of physics and basic laws but little experience in circuit design.

I'm trying to build a simple project involving a buzzer used as a warning. A very basic analogy is the beep on a reversing vehicle.

The requirements are that the buzzer is tested on startup (like ignition in the vehicle case) and is activated when a switch is operated (reversing gear is engaged). If the buzzer fails, it should not be possible to pass the current (shouldn't be able to reverse).

The end goal is to switch a valve on and off with a beeping signal when it is switched on.

I am doing some reading at the moment to get my head around things. I'd appreciate any advice on what components besides the buzzer and probably a relay would be best to use and any patience you can spare for me in pointing me in the right direction.

Many thanks!

 

Hi, welcome to the forum!
What you ask might be a little tricky, on what principle do you plan to test that the buzzer is working? Acoustic, electric ...?
Also, what happens when the buzzer stops working when the valve is open, should the valve close?

 

Hi, welcome to the forum!
What you ask might be a little tricky, on what principle do you plan to test that the buzzer is working? Acoustic, electric ...?
Also, what happens when the buzzer stops working when the valve is open, should the valve close?

Thank you for replying. It would need to be an electrical check that the circuit is working. It would be good to have the valve close if circuit failure occurs but I don't think this is absolutely essential since the system will remain secure even if the valve fails.

 

What kind of buzzer do you want to use, and what failure modes do you expect it could have? I can imagine it becoming open circuit, and possibly a short circuit. Both should be possible to detect with some fairly simple circuit. Are there any more, like a torn membrane or something that would electrically seem ok, but would fail to make sound?

 

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A standard piezo buzzer would be alright. Yep, if open/short circuits do occur I'd like that to stop the continuous beep of the buzzer and if the buzzer membrane is torn then no current should be passed to the valve, in either case signalling that something is wrong.

 

... if the buzzer membrane is torn then no current should be passed to the valve, in either case signalling that something is wrong.

That is the problem, how do you plan to detect that? Or say the piezo is full of water so the piezo is vibrating but very quiet... There could be a lot of other failure modes that are possible where you cannot simply detect by electrical measurements of the piezo.

What are the risks if this system fails? Material damage, minor injuries, severe injuries, death, explosion of a chemical plant...? This will mainly dictate how good the system needs to be in order to minimise the risk to acceptable levels.

 

...There could be a lot of other failure modes that are possible where you cannot simply detect by electrical measurements of the piezo.

I suspected this is what you were trying to highlight in the previous post and it is what has been causing me a bit of trouble.

What are the risks if this system fails?

There is possibility of injury as a heavy object is being attached/disattached but this is accounted for by a mechanical system that prevents this from happening (even if the valve breaks). According to the spec - attachment/disattachment should not be possible if the signal fails due to electrical circuit failure - I would suppose that this includes the function of the buzzer.

Thanks again for taking the time to reply.

 

Would this require a MCU?

 

I don´t think you need an MCU for this. Does the buzzer buzz by itself when connected to voltage, or is there some circuit that drives it with a square wave?

 

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Its a continuous buzz for the moment so eventually I'd like to do something to drive it with a square wave.

 

If this is going in any sort of industrial application I would suggest something along the lines of a Mallory Sonalert buzzer which come in assorted volume levels and include a light. Something like this. I would either include a "press to test" function or since it will squawk at startup make sure the operator notes the light and audible in their startup procedure.I would combine audible and visual warning rather than just audible. A Google of Mallory Sonalert Devices will reveal dozens of combinations. Mallory being only an example.

As to startup in an industrial environment I would consider a commercial off the shelf "One Shot" timer which triggers on startup. Macromatic makes a large line of relay type timers including "one shot" which I suggest. Macromatic just is another example of what is out there, there are dozens of one shot timing relays to be had.

Last, I have not seen any mention of control voltage? Most large industrial machines have a control panel and a control voltage like 24 VDC or 24 VAC?

If you have a drawing of what you currently have it would go a long way in giving you more ideas and help.

Ron

 

Thanks for all that information.

I would either include a "press to test" function or since it will squawk at startup make sure the operator notes the light and audible in their startup procedure.I would combine audible and visual warning rather than just audible.

A combined visual signal could be an option. Unfortunately it has to be automated at startup and not a press-to-test function.

As to startup in an industrial environment I would consider a commercial off the shelf "One Shot" timer which triggers on startup.

Great, I have a little 3 second relay that I think will serve purpose here.

Last, I have not seen any mention of control voltage? Most large industrial machines have a control panel and a control voltage like 24 VDC or 24 VAC?

Yep this will be part of it too. Some machines are 12V and others work on 24V but I'm trying to get something working on 12V for a start.

If you have a drawing of what you currently have it would go a long way in giving you more ideas and help.

Completely understand and I'm sorry for not providing more details initially. I'm working on this right now.

 

A combined visual signal could be an option. Unfortunately it has to be automated at startup and not a press-to-test function.

That's no problem as based on a 12 VDC control panel then on startup 12 VDC happens and thet becomes your trigger for a one shot meaning that on startup the one shot will output a pulse of a given duration and that pulse runs your buzzer or sound device and a lamp. The scheme is following that test then anytime something else you wish to trigger the audible & lamp will trigger it just like startup. For example if the machine is placed in reverse for example a signal from that action would turn on your audible. Do you have a drawing of the existing control panel?

Ron

 

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Here is my terrible attempt at drawing a circuit (I absolutely butchered the symbols, sorry) from a box that is wired similarly. I don't fully understand it if I'm honest.

There is a connector inside of it - I've drawn how the cables correspond and how the relay is wired. There are two diodes on the connector. I'm not entirely sure how the switch is wired so I left it blank in the middle - it's a Carling Technologies rocker switch and 4 of the 6 pins have wires connected to them.

Would this work correctly? I'm thinking that the dark blue wire going back to the (external) plug which signals the valve to open might get activated when the buzzer is initially 'tested'.

 

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Just to add to that, the above circuit uses a Carling Tech V-Series switch, and a 12V Durite 3s Timer Off Relay and a standard-looking buzzer.