Eletronic stethoscope but different intent!

[D Ryan]

This is my first post! I am new to electronic's, I have a radio shack learning lab, only done a few things with that!

Would this project be a good one for my learning lab?
http://www.electronics-lab.com/projects/science/003/index.html

Most of the threds I have read are member wanting to detect heart beat!

What I have in mind is a little different I don't know if it can be done the way I want it to.

I want to detect the clicking of a fuel injector coil going off an on! I don't want to listen , just the LED blink is fine.

In the plans there shows a OPTION to add LEDS! Could I just build that and eliminate the head phone part of the plans?

I would also like to have a prob to reach into a running engine and touch hard to reach injectors for the sound pickup.

Any help with this?

 

[Hero999]

This circuit won't differentiate between one sound and another, that's much more difficult to do.

It sounds like you're doing it the hard way. Why not connect an LED and resistor across the injector coil, or if you don't want to make physical connection, use a coil to detect the injector coil's field.

 

[D Ryan]

This circuit won't differentiate between one sound and another, that's much more difficult to do.

It sounds like you're doing it the hard way. Why not connect an LED and resistor across the injector coil, or if you don't want to make physical connection, use a coil to detect the injector coil's field.

From the circuit descritpion:

U1b operates as a low-noise Sallen and Key, Butterworth low-pass-filter with a cutoff frequency of about 103Hz. R7 and R8 provide a gain of about 1.6 and allow the use of equal values for C3 and C4 but still producing a sharp Butterworth response. The rolloff rate is 12dB/octave. C3 and C4 can be reduced to 4.7nF to increase the cutoff frequency to 1KHz to hear respiratory or mechanical (automobile engine) sounds.

I have a sepehoscope from harbor freight I can just place it on the running injector and hear it "snap" on problem!
I dont like wearing it around moving parts and 100K volts!!

Some of these injectors are hard to get to! Infact some engine dis-assembly is required to get to them, and thats just to check them for mechanical movement. Doing this with a prob using sound or light short-cuts this whole process, for the shade tree DIY'er!

I did some experment today with a earphone,I hooked the ear phone to my meter and a red LED , when I tapped the earphone the LED blinked dimmly and got a reading of about 29.0 MV, AC. Tap  was more like a slap!

Thanks for your thoughts!

 

[Hero999]

From the circuit descritpion:

• U1b operates as a low-noise Sallen and Key, Butterworth low-pass-filter with a cutoff frequency of about 103Hz. R7 and R8 provide a gain of about 1.6 and allow the use of equal values for C3 and C4 but still producing a sharp Butterworth response. The rolloff rate is 12dB/octave. C3 and C4 can be reduced to 4.7nF to increase the cutoff frequency to 1KHz to hear respiratory or mechanical (automobile engine) sounds.

I know it can pick up engine sounds. My concern is that the flashing LED part may not work as there are many harmonics given off by the engine. If you just want to listen, then fine but don't expect it to be able to flash the LED every time the injector fires.

I have a sepehoscope from harbor freight I can just place it on the running injector and hear it "snap" on problem!
I dont like wearing it around moving parts and 100K volts!!

Fuel injectors are powered off 12V. The only high voltage present in a car is the ignition system and is typically no more than 10kV.

I did some experment today with a earphone,I hooked the ear phone to my meter and a red LED , when I tapped the earphone the LED blinked dimmly and got a reading of about 29.0 MV, AC. Tap  was more like a slap!

You've got your prefix wrong there, you mean 28mV which is just 0.028V which is nothing, and you must've got the decimal place wrong as it isn't enough light an LED.

 

[D Ryan]

I know it can pick up engine sounds. My concern is that the flashing LED part may not work as there are many harmonics given off by the engine. If you just want to listen, then fine but don't expect it to be able to flash the LED every time the injector fires.


Fuel injectors are powered off 12V. The only high voltage present in a car is the ignition system and is typically no more than 10kV.


You've got your prefix wrong there, you mean 28mV which is just 0.028V which is nothing, and you must've got the decimal place wrong as it isn't enough light an LED.

I tryrd it again, this time I used a min-max meter! 79.4 MV AC, Led light every time!

I see what your saying! The circuit will recieve any signal and light the LED. Maybe some kind of sensativity can be added to it.

Also noticed the harder I hit the earphone , the more voltage, and of course the brighter the light!

Here is a picture of a fuel injector sound wave, it might be that there will be light on the LED at all times but only brighter light when pintel snaps. Just guessing!!
Right now I'm trying to figure a wat to bench test this theory!! Any idea's!

http://ecomodder.com/forum/member-superturnier-albums-injector-opening-delay-picture2854-injector-voltage-signal-injector-sound-signal-resolution-between.html


That Link has 3 pictures in it!  I only assume that the recording on the meter is while the engine is running! The 3rd pic showes a piezo-ele device attcheted!

I'm beginning to think that my choice of circuits to build is a poor one!!
Thanks
Denny

 

[Hero999]

I tryrd it again, this time I used a min-max meter! 79.4 MV AC, Led light every time!

Wrong prefix again, 79.9MV is 7990 000V, 79.9mV is only 0.079V
http://en.wikipedia.org/wiki/Metric_prefix

An  LED needs at least 1.8V to work. My guess is the actual peak voltage is more like 3V but it's so brief your meter doesn't have time to respond to it. If you connected it t an oscilloscope, you'd probably see a 3V pulse.

Don't forget this is with you tapping the ear phone so the voltage will be much higher than if you were to place t next to a noisy object.

 

[D Ryan]

Thanks Hereo999

Again I hooked it up to the Fluke 116, this time to auto Loz, I got no reading at all but the LED would flash! So it has to be to fast for the read!

Thanks again