optional piezo buzzer for EGT

[b00sted99-X]

i recently got an HKS peak/hold/warning EGT gauge but haven't installed it yet. i was reading over the instructions and it shows how to hook up a 'piezo buzzer' to go off when the warning level on the EGT is hit. anyways, i picked up a piezo buzzer at radio shack, a 12v unit and its very small. it only has two wires, red and black, i assume power and ground as usual. however the diagram on the EGT instructions show the use of a diode and a relay going to the ignition and all this other mess to hook up the buzzer... i don't understand electronics so can someone please decipher this, and also is it necessary? for what reason are they using all this extra stuff off the brown wire? i, in my naiveness, would have thought you just hook up the red wire from the buzzer to the brown wire off the gauge harness, and then ground the black wire. oh yeah the brown wire is the wire you use for the piezo buzzer.. it says so in the instructions.

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and HERE is the page it came off of.. with a few more details.

 

[95talontsi]

brown wire is what connects the buzzer?? I see after the relay a buzzer, and that just connects to the ground.

 

[b00sted99-X]

yea brown wire is off the EGT gauge, specifically for an optional buzzer or alarm. i just don't know if its necessary to run a diode and a relay for the buzzer.. it seems as though it should be way simpler than that.. i mean just attach the brown wire to the power lead of a the buzzer, and ground the black wire. but then again i don't know anything about electronics and am just guessing.

looking for an explanation as to why the diagram is laid out the way it is, and if anyone's installed a piezo buzzer on their EGT how did you wire yours up?

 

[RocketDSM]

The diode is not technically required, but it helps. I can see the diode doing two things. Preventing feedback due to the coil of the relay mixed with the ignition system, and ensuring correct current flow. After all, that is what a diode does. Anyway, for best operation, keep it as shown in the drawing. If you hook the buzzer directly to the iginition it can easily cause fluctuation on your ignition system as the voltage and current varies when the buzzer goes off. By using the relay and diode you can isolate a lot of it. Not all, but a lot. With another diode between the tie point after the relay and before the ignition you could isolate 99% of the fluctuation. Problem with all this is to do it right would require a breadboard to mount this stuff on. You can probably get away with using wire and solder for exactly what they have shown and get about 75-85% efficiency (I would estimate about 80% attenuation of fluctuations). If you want more info, ask. I'm an electronics guru for the Navy. They spent two years and $350,000 teaching me this stuff, I might as well use it.

 

[Enigma_Man]

I don't understand wtf they're using the ignition wire for anyway.
Why bother even bringing that into the mix?

-Jesse (going to be senior year electrical engineering student)

 

[b00sted99-X]

yes i'm having trouble understanding why the buzzer is wired to the ignition... maybe the brown wire isn't a power source? just a sender of some sort? i am absolutely lost thanks for the explanations guys

 

[Turbo Guru]

OK, if you are useing a standard +12V 30A relay look for the numbers on the bottom and connect it this way.

coil;
85 - +12V IGN source (IGN so the gauge is only on when the car is and the buzzer likewise.)
86 - Buzzer source - brown wire( assumed ground when buzzer is triggered.)
*note* check to see if the gauges output is +12V or Ground (I figured ground from the above diagram) when triggered, if it is +12V then changes must be made to the above coil instructions.

switch poles;
87a - Do not use
87 - buzzer positive (red wire)
30 - +12V IGN source
Buzzer (black wire) - Ground

*note* I did not use the resistor in this description, you may need it. It would go on one of the coil wire supplying buzzer activation to prevent feedback to the gauge (make sure the diode faces the right way or it will not work.)

Hope this helps,
Joe

 

[RocketDSM]

1) there is no resistor in the schematic...

2) the brown wire HAS to be a source voltage of some type since it shows the buzzer connected directly to ground on the opposite edge...

3) since the trigger voltage only has power available when the gauge is powered, as long as the gauge is only wired to be on when the ignition is on there isn't a problem.

as far as the diode, good point. Remember the cathode (the side with the line in the schematic) is the end that is marked. I made that mistake when building a bridge rectifier for my lighting system and blew my stereo amp (long story).

 

[Turbo Guru]

1) oops, I meant diode not resistor, thanks for catching that.

2) The brown wire appears to be ground output when activated (buzzer triggered by gauge.) The coil requires one of the poles to be + and the other - to throw the switch. If 85 is 12V IGN power and 86 (the other side of the coil) is disconnected from ground... until the gauge throws it a ground from the brown wire to activate the buzzer.

(the brown powers the relay, not the buzzer directly.)

3) A safety thing, there is no reason to have a constant +12V powering this relay. Since it is only to be used when the car is on there is no problem with the operation of either. But, IMO it would be easier to tap 85 and 30 off the same source which is IGN.

Thanks for the correction,
Joe

 

[Puke]

I have never connected one of these but here's my take(very similiar to what has already been posted):

It kind of looks to me as if the brown wire goes to the gauge and the gauge determines when the that wire gets grounded with resistance in line with the ground side inside the gauge.(Wouldn't want a short!)

I would still use the diode, it's not hard to install and a very cheap insurance policy to prevent reverse biasing.

It looks like the ignition signal is just a power splice.

Oh, theoretically, you could probably just use the buzzer, but it would DRASTICALLY decrease the life of the buzzer and possibly damade the gauge(too much current!) if you did it that way and if you did do it that way I would still use a diode in parallel with the buzzer.

I would just stick to the schematic!!

Hope that helps!