# Is remote started car running?

#### dknguyen

##### Well-Known Member
Just a LED and resistor on the digital output. That part worked fine but setting the threshold was the problem. Too much hysteresis between on and off.
I agree with crutschow's implication. A comparator will fix that "hysteresis" problem. It's not really hysteresis but w/e.

#### dr pepper

##### Well-Known Member
Ok non invasive no contact, nad electrically simple.
A largeish coil on the garage floor under the engine, a high gain amp to pick up the electrical noise generated by the vehicles electrics providing a digital output.

#### AGCB

##### Member
I agree with crutschow's implication. A comparator will fix that "hysteresis" problem. It's not really hysteresis but w/e.
I've used comparators but how would that work here?

#### dknguyen

##### Well-Known Member
I've used comparators but how would that work here?
You provided no information about your sound detector, but if it is what I am imagining that it is, then put the comparator between the digital output of the sensor and the LED and resistor. In other words, have the sensor drive the comparator have the comparator drive the LED.

That way the comparator decides when the LED turns on at any sound level and hysteresis you want, whereas before the LED would only turn on when the volume produced sufficient power to directly drive the LED.

#### AGCB

##### Member
Ok non invasive no contact, nad electrically simple.
A largeish coil on the garage floor under the engine, a high gain amp to pick up the electrical noise generated by the vehicles electrics providing a digital output.
I thought of something like that but I'm not too good with that sort of design. I don't want you to design something for me but would you point me to more info. It's the AC part of this that I have no experience with.
Thanks

#### dknguyen

##### Well-Known Member
You provided no information about your sound detector, but if it is what I am imagining that it is, then put the comparator between the digital output of the sensor and the LED and resistor. In other words, have the sensor drive the comparator have the comparator drive the LED.

That way the comparator decides when the LED turns on at any sound level and hysteresis you want, whereas before the LED would only turn on when the volume produced sufficient power to directly drive the LED.
Oh wait, a second you said your sound detector has a digital output. Yeah...not that won't work then. Need to be analog.

#### dr pepper

##### Well-Known Member
Well I'm happy to help you, however designing & building by proxy isnt easy or a good idea, maybe stick to something your comfortable with.
If I was to start something like this, and you are determined to have a go, and presuming you have a 'scope I'd make a coil about 2' diameter or maybe just a reel of wire and bung it under the engine & 'scope the output, if you only get a few 100uV its not a good idea, but if you get an o/p in the order of mV then an op amp and a 555 would probably do the trick.

I googled but couldnt find anything like the above, I did find this though, maybe you could fit something like this to the vehicle and use its o/p to trigger a radio module or an infra red Led to signal to another device in the garage:

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#### crutschow

##### Well-Known Member
Since those sound detectors you bought have a digital output, you might try buffering them with a transistor (2N3904 or similar) to drive the LED and see if that makes a difference.

Otherwise you can send their amplified analog sound output to an external comparator, such as an LM339, and adjust its sensitivity (trigger point) to your liking. The comparator will turn on when the audio signal peaks exceed the comparator trip point.
The LM339 output then drives the LED.

#### Frozenguy

##### Member
Do you use microcontrollers at all? If so, a cheap vibration sensor ($0.30) can be taped/blued/ziptied to the engine and then wired to an interrupt pin on a ($1.27) ATtiny85. ATtiny85 then makes an output high which an ESP8266 or RF module reads, then sends it to a second ESP8266 or RF on your garage windowsill, and then that shines an LED to your house. The car side of this solution is compact, fits in your hood forever, and runs off your battery without draining it.

Avoiding microcontrollers; you can put a temperature sensor with a comparator on the garage door/wall somewhere behind the car exhaust. It doesn't have to be exact. When the car starts, temperature behind the car will significantly increase especially if it's cold outside (needing the remote start). Wire that to your LED on the window.

#### camerart

##### Active Member
Hi A,
As mentioned before 'dashboard sensor' There is a wire that goes to the igniton light, that is sometimes used for leisure battery relays. This could be used for detection.

If you are happy with a wire that needs to be disconnected before driving, then a lead to 'as mentioned' a light on the garage or somewhere it can be seen, even in the house. Or a radio connection.
Camerart

#### AGCB

##### Member
Do you use microcontrollers at all?

Avoiding microcontrollers; you can put a temperature sensor with a comparator on the garage door/wall somewhere behind the car exhaust.
I have used Arduino's some and PIC's and Propeller's much.
I like the idea of sensing exhaust temp.

I'm still working on the sound device. Have some stuff coming today that was not in my junk drawer.

If you are happy with a wire that needs to be disconnected before driving
NOT good for the wife!!!

Thanks for all replies.
Aaron