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audio input to Nexus phone

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kinarfi

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I have a motor home without a tachometer, some salvaged electret microphone elements, and an app for my Nexus phone that "listens" to the sound the motor and tells me the RPM of the engine. I'm thinking that as I roll down the highway, there will be too much noise in cab for it to work and want to put a pickup near the motor, but I'm don't know how to feed the signal to the phone.
Anyone know how to do this?
Thanks,
Jeff
 

dr pepper

Well-Known Member
Most Helpful Member
Try using the headset connector socket on a remote mic.
Heres a schem of a headset, you could leave out the earpiece and pushbutton section.
http://forums.androidcentral.com/sa...adset-mic-button-wiring-schematic-pinout.html
Obviously you'd need screened cable to avoid pickup from the engine control.
And if for some weird reason your phone needs to 'see' the earpieces to work properly you could sub them for 33 ohm resistors.
 

kinarfi

Well-Known Member
The most important thing I have learned so far is the plug configuration and the presence of the microphone ring, I had no idea it was there, so that take care of where to input the signal, now, how to prepare the input signal so it is usable by my phone. I believe I can find that information but if someone already knows what I need and wants to share, I would sure appreciate it. I plan to use the electret mic I have but I also see where it needs a small voltage for it to work, that wouldn't be a problem, I think.
 

dr pepper

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I would have thought the phones original headset mic is an electret, if you get a 4 pin 3.5 jack, stuff it in yer phone then meter the mic connection that'll tell you if theres a bias voltage there or not.
The phone will have all the neccessary gizmo's to prepare the signal, only if you were using a dynamic mic would you need to do anything.
 

kinarfi

Well-Known Member
Thanks, I'll let you know what happens when I get this done, busy with other project right now.
 

kinarfi

Well-Known Member
It works, what I did was put an O-ring on a regular 3 terminal ear bud cord and use right side out as ground and ground a + voltage, 1.65 if I remember right. I tucked the mic end into the engine compartment and went for ride and the audio tach worked, but poorly, need to put the mic in a better place. Now that I know it will work, I'll probably go get the correct plug.
 

dr pepper

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Excellent.
I wonder if wind noise from the motion of the vehicle or from the radiator fan is overloading the mic.
 

kinarfi

Well-Known Member
I agree, since all I did for placement was get it near the engine, but now that I have a few more facts, 1.6 volts is enough to drive an LED, how many uamps will that take...., or maybe a hall device and since all the electret mike did was create a wave form, maybe I can make a better wave form. The bottom of the engine is easy to get to, so if i make a white spot on the belt drive on the front of the engine ..... maybe tape a vane to it and place the mike close to that, maybe put the mike in the air intake manifold, I like this idea, i wonder how much current is available.. It's early, I just got up, sorry for rambling, I let you know how putting in the intake works. I think the app on the phone was meant for something like rotor blades or exhaust pipe sounds,, maybe try a different mike
Jeff
 

dr pepper

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Mike in the intake probably isnt good due to the wind noise again.
A piezo disc on the engine might work well, as it would be more sensitive to mechanical vibration that sound, which is what you want, if you do that you'd need a 1uf cap inline to block the dc.
1.6v might drive a red led, not any other colour though. 3-4ma will light one, 15ma would be nice and bright.
If you use a slotted switch or some other pickup assuming its a 4 cylinder motor you'd need 2 white spots or 2 pulses per rev from the motor, a v6 would need 3, a v8 would need 4, a detroit screamin v8 diesel would need 8.
 

kinarfi

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The engine is the Triton V10 in a 97 motor home that has no tach which I feel is needed, especially on steeper hills where I have to gear down and I pull a trailer with a SBS on it, see avatar. The app is "RPM Gauge", there may be better apps available, the choice of the intake is based on the having had the intake for the previous SBS with it's intake snorkeled up out of the dust and too close to my ear and the sound from that, actually, the intake noise is nearly as loud as the exhaust, I'll make a recording for you :)
 

dr pepper

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Most Helpful Member
Ok then.
If its a 4 stroke you'll need 5 pulses per rev.
 

kinarfi

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I kind of think the audio approach isn't going to work, I don't think the app is sophisticated enough to handle the sounds from a 4 stroke Ford 6.8-liter Triton V10 engine, I thought the intake would be a good place to get some good sound, but it goes a way when you close the throttle which could be bad when going down hill and using the engine to slow you down, the 2.5 volts from the phone won't drive a hall effect, I think I'll give up on this and get a blue tooth Auto Car Obd2 Diagnostic Interface Scanner and the app for that, that should do away with my phone having to figure out if the rpm 1800 or 900 which it was having problems with
 

dr pepper

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Most Helpful Member
I have one, and I use torque for android, and I have to say its pretty good for the readies, if something went wrong you can read fault codes too.

Watch out for those obd to bluetooth modules, most of them stay powered up constantly killing the battery, I even got one that claimed to power down when the engine stops, it does, but only if you press the power button, con.
They do make them that shut off at zero rpm, but you pay a little more for those.
You can even buy them with a built in gps and cell phone interface so you can keep track of someone, and how they drive.
 

kinarfi

Well-Known Member
Thanks for the warning, sounds like it may need to be rewired to power up with the ignition circuit, I've been working to keep the batteries from draining, put in a mechanically latching relay to shut down power to the camper and built a circuit that brings in a 40 amp relay 20 secs after the ignition powers up to tie the camper batteries to the alternator. It had dual diode isolator, but burned up. Waiting patiently for OBD2 to get here. What model brand, model did you get?
Jeff
 
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