Hi All,

I’m new to working with electronics and I’m currently building a small project for a local war games centre.

This is what I need to happen:

12v DC power supply – this is turned on by a toggle switch – which then sends power to a Time Delay Relay ( a time of 5 minutes is needed) – after the 5 minute period the power is sent to a small 12v Buzzer – this is reset by turning the toggle switch off.

I need help with the delay relay, what type will I need? (Can any one suggest one to operate on 12v with low amps?)

I think it is an On Delay Relay I need? If so how would I wire this up with the pins? I.E input voltage goes where (to what pin number) and out put wires (that go to my buzzer) goes where etc?

And finally will I need another switch after the delay relay? Or will the time delay relay work as a switch and turn my buzzer on?

Any suggestions on the above would be greatly appreciated.

Thanks
Billy

 

You can do this all in electronic components much cheaper than using a relay if the only load is a buzzer.

Can you use pushbutton switches, one to start the timer and one to reset it?

 

I'm only going to use a buzzer to test it initially, however it may be a 12v car horn this was why I was thinking of using a relay? It may also take some led's to light it up also, not really that big a load tho.

Because several people will be using it I was thinking of just using a toggle or switch to turn it on (giving power to the timer relay) and when the buzzer goes off then just turn it off with the main switch again.

This will only be used once a game so if turning it off resets the timer delay this would be good enough.

thanks for the reply,

billy

 

Essentially you just need a 5 minute timer with audio alarm. If you do not have soldering iron, flux, solder, proto board, electronic parts...etc. then you might just as well buy a simple stove timer, either crank or electronic for less than $10.
Timer

Otherwise you'll be spending well over $50.

 

I have soldering iron etc.

I don't think the buzzer on those alarms would be loud enough.

Its for an Airsoft Fake Bomb. The idea is that when playing airsoft at the war games centre. Then a player can plant the bomb, turn it on and then run. The defending players have 5 mnutes to turn the bomb off or they loose the game.

It will be constructed from plastic pipe etc with the car horn build inside the tube. A few flashing LED's to show that its on with a toggle switch to turn it on and off. The timer delay to change the times for different games.

 

A countdown timer that controls an AC outlet is a standard piece of lab equipment. You might be able to find one used for very cheap. It would give you the option of variable times, seeing the countdown time remaining, and so on. In other words it's a purpose-built machine to do exactly what you've described. No need to reinvent the wheel?

 

12V car horns often use quite a lot of current - several Amps might be typical, so you would need a pretty heavy battery. You might do better with a high-intensity piezo buzzer if you want to make this thing reasonably portable.

 

Sonalert and Klaxon even have sound samples online:
http://www.mallory-sonalert.com/3_1.htm
http://www.klaxonsignals.com/techinfo_new.asp?pageID=449

 

A pseudo circuit!
Adjustable Timer, but at about 12.5K - 13.5K you will have about 5 Minutes.
Other tweaks may be required.

 

Thanks very much for all the input. I think I'll have a go at the circuit above. All tho not sure of all the parts in the drawing. Could someone help and list the above parts to make sure I've got it right in my head? Also I live in the uk anyone know a good supplier to get the items needed for the above circuit? Many thanks all. Billy

 

Thanks very much for all the input. I think I'll have a go at the circuit above. All tho not sure of all the parts in the drawing. Could someone help and list the above parts to make sure I've got it right in my head? Also I live in the uk anyone know a good supplier to get the items needed for the above circuit? Many thanks all. Billy

Before you buy parts we need to know some more details about the Sorce voltage, the horn you have or want to use, and the color of LED indicators you want.

Are you going to use a 12V Lead-Acid battery? What is the AH rating. If you have a horn how much power does it consume and it's current needs (12V, 2.0A, 20W). What color LED's and how many do you want? Do you have a relay or do you need one. If you have one what are its specs, 12V, 5A, SPDT??? A fuse might also be good to have.

 

I think I will use one of those buzzers from earlier in the thread. 12v buzzer around 95db. The led is a 8mm blue led (prob three leds in total) which takes between 2.8 v and 4.0v max. As for the battery well i was going to use maybe use two of these:

LINK - battery

led - leds i have in the shed

buzzer - buzzer rather than car horn


I would need to get a relay fit for the job. Maybe a inline fuse just after the positive wire of the battery?

 

I think I will use one of those buzzers from earlier in the thread. 12v buzzer around 95db. The led is a 8mm blue led (prob three leds in total) which takes between 2.8 v and 4.0v max. As for the battery well i was going to use maybe use two of these:

LINK - battery

led - leds i have in the shed

buzzer - buzzer rather than car horn


I would need to get a relay fit for the job. Maybe a inline fuse just after the positive wire of the battery?

You will need 8AA batteries, will you use alkaline or Rechargeable.
the difference would be that with alkaline batteries you will get 12V, but with rechargeable batteries you will have aprox. 1.42V x 8 = 11.36V. The 12V buzzer would still work, but would be not quite as loud.

What would be the purpose of three LED's as apposed to just one? It's no big deal in the circuit.

With the buzzer you chose, a relay would not be necessary. Not sure a fuse would be necessary either unless you plan to operate it in the rain.

With those LED's we will assume 3.0V as Vf and for If, 17mA. You will likely never know the difference and you will insure that their lifespan is long.

 

Ahh, that circuit will only time for 0.5 seconds, not 5 minutes. Someone missed a few decimal places.

If C1 were replaced with a 270uF cap, and R1 were a 910k resistor in series with a 250k pot, that should do the trick. Set the pot about centered to start off with, and adjust to compensate for capacitor variances. They're usually off a good bit from their markings.

 

How about this battery holder instead:
http://www.ebay.co.uk/itm/AA-x8-Battery-Holder-Black-12cm-Leads-/180690854983?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item2a1203a447

 

Ahh, that circuit will only time for 0.5 seconds, not 5 minutes. Someone missed a few decimal places.

If C1 were replaced with a 270uF cap, and R1 were a 910k resistor in series with a 250k pot, that should do the trick. Set the pot about centered to start off with, and adjust to compensate for capacitor variances. They're usually off a good bit from their markings.

A few decimal places is right! WOW! Ya saved me again... I think my pot was supposed to be like 20M or something.

Partial Parts List:
Ra - 750K
Rb - 250K Pot
R2 - 100 ohm
R3 - 1K
R4 - R6 - 560 ohms(subject to change)
C1 - 330uF
C2 - 10nF(.01uF) ceramic
C3 - 10uF electrolytic
Q1 - 2N3904 NPN or Equiv.
IC - LM555CN
Piezo - 95db, 15mA
LED 1 - 3 Blue, Vf - 3.3V, If - 20mA
SW1 - SPST Toggle
Batteries - (8) AA Alkaline
Battery holders (2) 4pk

 

Actually, I'm going to change numbers on you, because 270uF caps are a bit hard to find.

Instead of 270uF, go with 330uF; they are far more common. That means R1 needs to be around 820k instead, so a 750k resistor in series with a 200k to 250k pot should give plenty of adjustment.

 

Makes sense...

 

wow....Thanks for all the input guys.
Time for some shopping now I think. Any good shops in the uk sell these parts...maplins?.....digikey?.....

Is this the correct IC - link

 

It can be, but that's the surface mount (SMD) version. You probably want to use the DIP version, LM555CN.