Low voltage relays

[DarrenSV650S]

Do you get relays that operate with about 3V ? It needs to be able to switch 12V

[DarrenSV650S]

Baph!! Where are you

[Baph]

Sorry, I did mean to reply to this not long after it was posted originally.

This (http://parts.digikey.com/1/parts/756093-relay-2a-3vdc-140mw-smd-tx2sl-3v-z.html) will do you fine. Not sure of any other retailers. It'll cope up to 30V DC, but only at 2A.

If that's not suitable, then there's a few details you can give to help me find the right relay.

You say that the relay is to be activated by 3V, are you fussed about the current through the coil (as in the amps that you have on this 3V wire)?

What current are you wanting to give the 12V circuit? Do you want it to be NO or NC? (first one activates 12V when 3V is on, the other deactivates) Are you fussed about the number of contacts?

[tigersaw]

yes, but how much current?

You could make a driver circuit with a power transistor to utilise a normal 12v relay if necessary

[DarrenSV650S]

The original wiring was only powering a LED at 3.3V. Not sure about the current but I can find out. I want the relay to switch on the sv's standard horn when the LED wiring is live

[tigersaw]

ummm this isnt the gps inforad by any chance? :)

[DarrenSV650S]

ummm this isnt the gps inforad by any chance? :)
Yup:smt038

[tigersaw]

Now I see what you are up to. Mine alerted me to a right devious one today, but it was forward facing luckily.
I'd suggest driving a high frequency sounder or something rather than the horn - it will use low current, horn uses loads, and it might become embarrasing if your horn starts going honk honk honk honk whenever you are in traffic near say a red light camera and stationary

[DarrenSV650S]

Now I see what you are up to. Mine alerted me to a right devious one today, but it was forward facing luckily.
I'd suggest driving a high frequency sounder or something rather than the horn - it will use low current, horn uses loads, and it might become embarrasing if your horn starts going honk honk honk honk whenever you are in traffic near say a red light camera and stationary
I need to be able to hear it at high speed. I'm thinking of putting a switch in with the horn circuit so once it has alerted me I can flick it off. Then when the green LED comes back on I can flick the horn back on

[Baph]

Why not mount a light under the screen (top of the "dash") - a red LED is eye catching enough even on a summer's bright day.

I know first hand. :)

[tigersaw]

Good idea.
I'll trawl through the RS catalogue tomorrow if I have time, see what they have. Since the LED used very small current I dont think it will drive a relay directly, might be better to find a little circuit with a relay driver built in, and maybe then it can be simply modified to self cancel after a second or two

[tigersaw]

Why not mount a light under the screen (top of the "dash") - a red LED is eye catching enough even on a summer's bright day.

I know first hand. :)

Thats included, though I agree with the OP - its not enough

[DarrenSV650S]

I want a horn! *spits dummy* :lol: :lol: :lol:

I don't want to be constantly looking down to see if the light is on. I'd rather just not have to look. I've mounted the inforad's light in the hole in the stem because it was the neatest option I could think of. But because it is there I don't see it easily.

So is that first relay suitable baph?

[DarrenSV650S]

Good idea.
I'll trawl through the RS catalogue tomorrow if I have time, see what they have. Since the LED used very small current I dont think it will drive a relay directly, might be better to find a little circuit with a relay driver built in, and maybe then it can be simply modified to self cancel after a second or two
Oooh a self cancel would be great. I set the inforad to it's lowest setting but that still means it comes on 15 seconds before the camera, plus a little while after I've passed the camera

[Baph]

TBH, for your application, I wouldn't bother using a relay.

I'd do the following:

Buy a 12v transistor, and connect the emitter leg to ground. Your 3v pulse to the base leg, a 270 Ohm resistor to the collector leg, and the 12v supply horn wire to the resistor.

Don't put this between the horn & horn switch, but on the other side of the horn. Should work a treat as the SV horn is fed a constant 12v, and is only grounded when you hit the button. This is basically adding another switch capable of grounding the horn. :)

EDIT: Non of the above will achieve self cancelling... if you want that you're looking at using a timer as well probably.

[tigersaw]

just looked at some kits - about £6 for a kit that has a trigger input and adjustable timer output, and about £6 for a police siren, fire brigade, emergency vehicle and machine gun sound generator.
Thinking required to interface the timer kit to the inforad (which has a relay output for your horn), studied the cct of the siren, I reckon it would be pretty loud enough

[DarrenSV650S]

Baph I won't be using the original horn wiring. I've got that on a relay which is running a stebel horn. But the original horn is still on the bike so I can get a feed from the stebel relay to the original horn

Where did you see that kit tiger?

[tigersaw]

http://www.maplin.co.uk/Module.aspx?ModuleNo=25224 or
http://www.maplin.co.uk/Module.aspx?ModuleNo=3315

Both will need modifying

modify the trigger circuit and set output to say 5 secs.
be nice to make it so that when the red lamp is flashing it will constantly retrigger and cause a constant 'horn' - until red led is constant then it will time out.

I'm off to bed now, but I'll think about it further and try and knock something up in the coming week or two

[DarrenSV650S]

Thinking required to interface the timer kit to the inforad (which has a relay output for your horn)
Wouldn't I just connect the inforad's wires to the control side of the relay and then the other side would switch the horns feed?

[tigersaw]

Wouldn't I just connect the inforad's wires to the control side of the relay and then the other side would switch the horns feed?

Kind of. The timer chip on the board needs a -ve going trigger, so depends on how the LED is driven, switched earth or switched +3v. If switched earth its straightforward, if +ve, then it needs a transistor added as an inverter.
Going to order the board and a mini siren and have a fiddle.

[DarrenSV650S]

Kind of. The timer chip on the board needs a -ve going trigger, so depends on how the LED is driven, switched earth or switched +3v. If switched earth its straightforward, if +ve, then it needs a transistor added as an inverter.
Going to order the board and a mini siren and have a fiddle.
When I tested the green LED it was flashing (finding a signal) and the reading kept jumping up and down. When it found a signal it settled on 3.3V

Don't understand why it needs an inverter :smt017

[tigersaw]

When I tested the green LED it was flashing (finding a signal) and the reading kept jumping up and down. When it found a signal it settled on 3.3V

Don't understand why it needs an inverter :smt017

The LED could have a permanent +3.3V on the anodes, and illuminated by grounding the cathode - this is a common way of driving LEDs from IC's.

Equally it could have a perminant earth, and illuminated by sending +3.3V. In this case the 555 timer chip cannot be triggered directly, but adding a simple transistor inverter would sort it out.

Either way would read the same from a meter.

I have just ordered the timer circuit, I'll experiment when it comes.