Hey newbie here and hoping to draw on the expertise of the members here.
I am in the process of putting a big v8 in my Hilux and want to make sure it sounds the part. That in mind, I bought some HSV mufflers that are bi-modal meaning they have a vacuum actuator that opens a bypass causing them to be really awesome - big smiley face.

So I am wanting to make a small simple circuit to trigger a solenoid to use engine vacuum to operate the actuator making car sound great and put smile on Camos face.

The car is drive by wire meaning the accelerator pedal is a petentiometer but only has a 5v signal to the engine computer.

My outcome is to have the mufflers in 3
Modes:
Off - quiet to keep the neighbors happy early in the morning and sneaking home late at night.
On - always loud
Auto - at low throttle position is quiet and when you bury the pedal (say 70%+) they automagically open.

My concern is the signal is low voltage and would be extremely sensitive so don't want to disrupt that causing driving issues.

Have read on the forum about comparators, would this be the way to go or are there other ways to achieve big smile?

Thanks in advance.

 

Is this legal on your planet?

 

It certainly wouldn't be legal in the UK!

 

Is this legal on your planet?

No one would care here in the North Dakota.

That said, Yes a simple power Op-Amp working as a voltage comparator to trigger your solenoid that supplies the vacuum to the muffler cutout would work just fine.

Just use the 5-volt power as the supply for the reference signal and a pot between it and ground to provide a 0- 5 volt reference to the Op-Amps - input and put the throttle 0 - 5 volt signal to its + input that way whenever the throttle signal goes above the set reference voltage the Op-Amps output goes high which can then be used to activate the vacuum solenoid.

 

It is a grey area and I plan on exploiting it. They are factory fitted options in a few cars around the world and are a bit of a contentious issue.
In Australia they are tolerated as long as the db reading at its loudest option is still within the legal limit.

Thanks for the reply tcm,
By pot you mean potentiometer? My electronics is basic but understand the concepts, my electronics slang is woeful though.
Would it be better to use a 12v source to activate the solenoid rather than the 5v? Would it then draw some of the voltage sensitive load to activate the solenoid effecting the signal?

 

Does this look right do you think?
I have the pedal signal as one ref and an adjustable source as the other.
The capacitor and resistor is to keep the solenoid open for a few seconds after the pedal signal is lowered, giving a burbling effect as the engine speed slows down.
Or should the capacitor and resistor be straight after the pedal reference?

 

Yes that's sort of what I am referring to except the Op-Amp is driven by the normal 12 volts but its two inputs use the 5-volt system for their referencing.

The delayed off circuit you drew would be best placed on the input side not output side of the circuit.

 

Your a rockstar mate, thanks.

Would I need that resistor at the bottom in the set point reference side for some sort of load to prevent short? A 40k be enough?

 

You may need to add a vacuum tank to supply the vacuum for the valve, since the manifold pressure (vacuum) rises significantly at high throttle settings/acceleration, just when you need the vacuum.
One like this should work along with a check valve. to maintain the vacuum in the tank when the manifold pressure rises.

 

Does this look right do you think?
I have the pedal signal as one ref and an adjustable source as the other.
The capacitor and resistor is to keep the solenoid open for a few seconds after the pedal signal is lowered, giving a burbling effect as the engine speed slows down.
Or should the capacitor and resistor be straight after the pedal reference?

Without knowing the specifications of the solenoid in question...

It's doubtful that the opamp could drive the solenoid directly, you will need a transistor or MOSFET
I also second the idea of placing the delay components on the signal side of the opamp.

 

You may need to add a vacuum tank to supply the vacuum for the valve, since the manifold pressure (vacuum) rises significantly at high throttle settings/acceleration,

I beg to differ with this statement. Manifold vacuum is higher at idle/low speed than full throtlle. Unless your using one of the "ported" vacuum sources, like carburetors have, don't know if EFI even has a ported vacuum source though.

 

If you don't want to tap into the TPS you could pick up the pulses from the HT lead and use a frequency to voltage converter to feed a comparator. There may be tachometers available that have the facility to provide an output at a particular RPM.

On second thoughts; why not just fit a switch to the accelerator pedal?

 

A micro switch on the pedal sounds like a great, simple easy yet boring solution haha kidding.
The idea of the circuit is to give a short delay in closing when in auto mode and an easier way to adjust the opening point.
Tapping into by leads or tach signal is a great idea. Virtual beer coming your way.

Excuse my electronics ignorance, would you need a transistor or mosfet to amplify the signal in the comparator circuit? I imagine the 12v supply would be able to drive the solenoid.
The solenoid is only quite small and would draw only a small amount.

Really appreciate to input guys

 

I beg to differ with this statement. Manifold vacuum is higher at idle/low speed than full throtlle. Unless your using one of the "ported" vacuum sources, like carburetors have, don't know if EFI even has a ported vacuum source though.

By "higher manifold pressure" I meant a lower (poorer) vacuum under acceleration, where I believe the vacuum is needed to open the valve.

 

Without knowing the specifications of the solenoid in question...

It's doubtful that the opamp could drive the solenoid directly, you will need a transistor or MOSFET
I also second the idea of placing the delay components on the signal side of the opamp.

That's why I said POWER Op-Amp. The ones (like the LM1875 in 5 pin TO-220 case style) used for simple audio amplifiers can easily sink or source several amps of current without problems.

 

Thanks heaps for the input, I am going to start putting together the prototype and get it going.
My mufflers arrived today so am excited to get this working.

Next question and please tell me if is not possible or if I'm asking too much:
Can I wire up the circuit with a single push button switch?

That is use a single latched switch to toggle between Off, On and Auto.
I have seen momentary switches used to toggle between 2 circuits but is it possible to toggle between a 3rd (or off)?
And is it then possible to use a latched switch rather than a momentary switch.

Reason is I will have an unused button on the shift selector cover plate that was used to modify gear shift points and called a Power Button.
In reality it didn't do much and I will not be connecting it up and would like to use that button to turn the circuit to on and then to auto.

 

Not easily.

If it was me I would just use the potentiometer to control everything.

If you put a diode in series with the variable voltage feed coming from the throttle it would reduce that voltage reference by roughly half a volt which then if yo had the reference voltage pot turned all the way to 5 volts the Op-Amp would never change from low to high state thus working as an off position.

Same with the other end of the pot if set at 0 volts for a reference the Op-Amps output should stay on all the time being most throttle signal don't drop all the way to zero and if you did by chance then that could be cheated with a second diode in reverse parallel to the first one and high value resistor, like a 100,000 ohm, could be added between that input and the 5 volt supply so that the throttle signal voltage never drops below about half a volt at the other end of travel.

 

......................
Can I wire up the circuit with a single push button switch?

That is use a single latched switch to toggle between Off, On and Auto.
I have seen momentary switches used to toggle between 2 circuits but is it possible to toggle between a 3rd (or off)?
And is it then possible to use a latched switch rather than a momentary switch.
.......................

Yes, you could do that with a few flip-flops or counter.
But what is a "latched switch"?