Help needed to design and build trigger for Ambulance siren

[Les Desser]

Not sure if this is the right place to ask, but give it a go anyway.

I need a small switching device to trigger and stop an ambulance siren.
Can anyone help? I am totally ignorant in this matter and would be
willing to pay for the finished product. We are in London, UK.

The existing siren is a sealed unit and is triggered by the vehicle horn
button. The first tap on the horn starts it off with tone 1 which
continues until the next tap moved it on to tone 2 and then again for
tone 3 and round again.

A double-tap on the horn switches it off.

The next tap starts the cycle from tone 1.

What we need is a momentary activation switch pressed by the driver
which will:-

1. Simulate the horn tap (presumably just need to close a contact for a
fraction of a second)

2. Start a count-down timer (preferably user changeable) for x seconds
(probably 3-5 seconds)

3. After the x seconds it should simulate a double tap (close-open,
pause, close-open) to shut off the siren automatically.

The unit would need to be suitable to mount under the dashboard of the
ambulance with a push-switch on the dash. Working off 12-16V vehicle
supply.

Thanks.

 

[Homer J Simpson]

What we need is a momentary activation switch pressed by the driver which
will:-

You could use 3 12vdc delay relays if you don't want to do electronics.
Otherwise there are a number of electronic solutions including a BASIC stamp
microcontroller and related components: www.parallax.com

 

[Les Desser]

You could use 3 12vdc delay relays if you don't want to do electronics.

I could cope with stringing relays together! The only hit on Maplins is
<http://www.maplin.co.uk/module.aspx?ModuleNo=25224&doy=6m5> which is
not what I think you had in mind.

Other hits on Google also do not seem relevant.

What exactly did you have in mind?

Otherwise there are a number of electronic solutions including a BASIC stamp
microcontroller and related components: www.parallax.com

Anyone prepared to build one for us?

 

[Homer J Simpson]

I could cope with stringing relays together! The only hit on Maplins is
<http://www.maplin.co.uk/module.aspx?ModuleNo=25224&doy=6m5> which is not
what I think you had in mind.

Actually, yes. You may find it is cheaper and easier to use three of these
than to engineer a fancier solution.

 

[Les Desser]

Actually, yes. You may find it is cheaper and easier to use three of these
than to engineer a fancier solution.

I think I understand what is being suggested:-

1. Momentary push button triggers the siren and closes a normal relay to
supply continuous power to 2 delay 'on' relays. The 1st relay is wired
to maintain its own supply - to be subsequently broken in step 3.

2. The timing on the two relays to be set to within 0.5 seconds or less
of each other to simulate a double press on the horn.

3. The NC contact on the last relay to fire will open and cut off the
power supply to all relays. This assumes that the NC opens after the NO
contact closes.

Am I getting warm?

On further though that is not good enough. The first delay relay must
close and then immediately open. So it must cut off its own supply.

I do not have the spec of the siren as to how close the two pulses have
to be but would assume that 0.5 sec should do.

Could two delay relays be set to reliably fire that close together?

Links to suitable relays (preferably UK) would be appreciated. I cannot
quite see how I could use the Maplin offering.

Thanks Homer for your responses.

 

[Homer J Simpson]

Links to suitable relays (preferably UK) would be appreciated. I cannot
quite see how I could use the Maplin offering.

Thanks Homer for your responses.

IMO it's worth trying. Does this whole thing have to be triggered by the
horn - it can't be operated by a separate switch?

 

[Les Desser]

IMO it's worth trying.

I'm keen to give it a go as long as I can get hold of suitable relays.

Does this whole thing have to be triggered by the
horn - it can't be operated by a separate switch?

It is to be used separate from the horn. The horn functionality must
stay unaltered.

This new device would be triggered by a non-latching push-to-make
switch.

I am waiting for a spec of the siren system to see the min/max timings
and whether voltage needs to be applied or just a circuit closed.

 

[Ross Herbert]

Not sure if this is the right place to ask, but give it a go anyway.

I need a small switching device to trigger and stop an ambulance siren.
Can anyone help? I am totally ignorant in this matter and would be
willing to pay for the finished product. We are in London, UK.

The existing siren is a sealed unit and is triggered by the vehicle horn
button. The first tap on the horn starts it off with tone 1 which
continues until the next tap moved it on to tone 2 and then again for
tone 3 and round again.

A double-tap on the horn switches it off.

The next tap starts the cycle from tone 1.

What we need is a momentary activation switch pressed by the driver
which will:-

1. Simulate the horn tap (presumably just need to close a contact for a
fraction of a second)

2. Start a count-down timer (preferably user changeable) for x seconds
(probably 3-5 seconds)

3. After the x seconds it should simulate a double tap (close-open,
pause, close-open) to shut off the siren automatically.

The unit would need to be suitable to mount under the dashboard of the
ambulance with a push-switch on the dash. Working off 12-16V vehicle
supply.

Thanks.

There may be some statutory regulations regarding equipment which can
be used on emergency vehicles such as ambulances. The authorities may
not allow DIY sirens or controllers so you had better check to see if
only approved types (UK legal) can be used in your case.

It may be more economical to "go the whole hog" and lash out on a
controller off-the-shelf rather than DIY. Woodway Eng'ng in the UK
make a whole range of systems including sirens and controllers
http://www.woodway-online.co.uk/acatalog/sirens-section.html



eg. http://www.wolo-mfg.com/siren.htm (couldn't get sample sound#2 to
play)