Help needed to design and build trigger for Ambulance siren

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:

In article , Homer J Simpson Sun, 6 May 2007 17:40:40 writes

I could cope with stringing relays together! The only hit on Maplins is 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?

Anyone prepared to build one for us?

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

In article , Homer J Simpson Sun, 6 May 2007 21:56:56 writes

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.

1. 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.

2. 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.

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?

In article , Homer J Simpson Mon, 7 May 2007 18:53:13 writes

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

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.

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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

eg.