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Tundra10

Joined: 14 Jun 2010
Posts: 102
Location: Scarborough, Ontario

Posted: Mon Jul 18, 2016 10:16 am Post subject: Off Topic: Outboard Motor Tachometer

I am trying to read the rpm of an outboard motor by counting  

tachometer pulses with an Arduino board.



I have little information on the characteristics of the signal output  

from the outboard motor.  They all seem to be similar, providing 6  

pulses per revolution somehow produced from the alternator.



For starters, I assumed the signal would be vaguely sine or square  

waved pulses between 0 and 14V.  I used the comparator portion of an  

LM392N to condition the signal to the Arduino board.



One input of the comparator connects to 3.3V (which happened to be  

handy), assuming the pulse would go above and below that value.  I  

added a feedback resistor to provide about a 1V hysteresis spread.



The tach signal goes through a 100K resistor and has a 6.2V zener to  

prevent the value on the input pin going too high.



The comparator is powered with a clean 8.3V regulated voltage from an LM317T.



I have a cheap signal generator that will produces a square wave of  

sufficient voltage to activate the circuit, and I have validated the  

frequency injected is correctly read by the Arduino software, to  

frequencies higher than the operating speed of the engine.



However, when I connect the circuit to read the signal from the  

outboard motor, it counts zero pulses.



So, now my question:



Does anyone have any knowledge of the characteristics of the tach  

signal from the motor ?



It would be difficult to run a very long extension cord to the dock to  

try to watch it with an oscilloscope.



Googling "outboard motor tachometer schematic" got me many wiring  

diagrams instead.



Thanks !



Jeff Page

Dream Aircraft Tundra #10



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yellowduckduo(at)gmail.co
Guest

Posted: Mon Jul 18, 2016 11:23 am Post subject: Off Topic: Outboard Motor Tachometer

Jeff

I run an oscilloscope off a little inverter and a 12 volt booster 

battery when AC power is not available. It is usually time consuming and 

frustrating doing this kind of project without a scope even when I think 

I have a good idea of what the signal is "supposed" to look like.  I've 

seen tach signals that are quite different from what the documentation 

claims. A lot of those ic's won't tolerate signal voltages that go above 

or below power supply voltage.  For temporary measurements I find an 

ebay optical tach handy.  Around $10. delivered. I've used a number of 

arduinos for various displays with great results but they usually end up 

taking a lot more time than I expected.

Ken

do not archive



On 18/07/2016 2:13 PM, Jeff Page wrote:

 	  Quote: 	
		   



 I am trying to read the rpm of an outboard motor by counting 

 tachometer pulses with an Arduino board.



 I have little information on the characteristics of the signal output 

 from the outboard motor.  They all seem to be similar, providing 6 

 pulses per revolution somehow produced from the alternator.



 For starters, I assumed the signal would be vaguely sine or square 

 waved pulses between 0 and 14V.  I used the comparator portion of an 

 LM392N to condition the signal to the Arduino board.



 One input of the comparator connects to 3.3V (which happened to be 

 handy), assuming the pulse would go above and below that value.  I 

 added a feedback resistor to provide about a 1V hysteresis spread.



 The tach signal goes through a 100K resistor and has a 6.2V zener to 

 prevent the value on the input pin going too high.



 The comparator is powered with a clean 8.3V regulated voltage from an 

 LM317T.



 I have a cheap signal generator that will produces a square wave of 

 sufficient voltage to activate the circuit, and I have validated the 

 frequency injected is correctly read by the Arduino software, to 

 frequencies higher than the operating speed of the engine.



 However, when I connect the circuit to read the signal from the 

 outboard motor, it counts zero pulses.



 So, now my question:



 Does anyone have any knowledge of the characteristics of the tach 

 signal from the motor ?



 It would be difficult to run a very long extension cord to the dock to 

 try to watch it with an oscilloscope.



 Googling "outboard motor tachometer schematic" got me many wiring 

 diagrams instead.



 Thanks !



 Jeff Page

 Dream Aircraft Tundra #10



 DO NOT ARCHIVE

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ceengland7(at)gmail.com
Guest

Posted: Mon Jul 18, 2016 11:42 am Post subject: Off Topic: Outboard Motor Tachometer

On Mon, Jul 18, 2016 at 1:13 PM, Jeff Page <jpx(at)qenesis.com (jpx(at)qenesis.com)> wrote:

 	  Quote: 	
		  --> AeroElectric-List message posted by: Jeff Page <jpx(at)qenesis.com (jpx(at)qenesis.com)>

 

 I am trying to read the rpm of an outboard motor by counting tachometer pulses with an Arduino board.

 

 I have little information on the characteristics of the signal output from the outboard motor.  They all seem to be similar, providing 6 pulses per revolution somehow produced from the alternator.

 

 For starters, I assumed the signal would be vaguely sine or square waved pulses between 0 and 14V.  I used the comparator portion of an LM392N to condition the signal to the Arduino board.

 

 One input of the comparator connects to 3.3V (which happened to be handy), assuming the pulse would go above and below that value.  I added a feedback resistor to provide about a 1V hysteresis spread.

 

 The tach signal goes through a 100K resistor and has a 6.2V zener to prevent the value on the input pin going too high.

 

 The comparator is powered with a clean 8.3V regulated voltage from an LM317T.

 

 I have a cheap signal generator that will produces a square wave of sufficient voltage to activate the circuit, and I have validated the frequency injected is correctly read by the Arduino software, to frequencies higher than the operating speed of the engine.

 

 However, when I connect the circuit to read the signal from the outboard motor, it counts zero pulses.

 

 So, now my question:

 

 Does anyone have any knowledge of the characteristics of the tach signal from the motor ?

 

 It would be difficult to run a very long extension cord to the dock to try to watch it with an oscilloscope.

 

 Googling "outboard motor tachometer schematic" got me many wiring diagrams instead.

 

 Thanks !

 

 Jeff Page

 Dream Aircraft Tundra #10

	
 

 No idea on the tach signal from the motor, especially without knowing which one. But...

Is the arduino method a requirement? If not, why not a Tiny Tach?

 https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=tiny%20tach

Probably cheaper than the sum of all hardware needed for the arduino, and once you supply power & wrap the sense wire around a spark plug lead, you're done.

If the arduino is a requirement, you could probably get it to sense the plug wire like the Tiny Tach does.

If you want to know what the tach pulses look like, you could play with an O-scope on your phone.

https://retronics.wordpress.com/2012/07/14/the-0-android-oscilloscope/



(Just the 1st link I hit when I googled it.)

Charlie

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Tundra10

Joined: 14 Jun 2010
Posts: 102
Location: Scarborough, Ontario

Posted: Mon Jul 18, 2016 11:51 am Post subject: Re: Off Topic: Outboard Motor Tachometer

Ken,



If I have to, I can run an extension cord to the dock for the oscilloscope (my ancient one would require a much bigger inverter than I own).  If no one can tell me the signal characteristics that indicate obvious changes to the circuit, I will do that, but hopefully someone will say "just try this" and minor circuitry changes will have it working.



The boat has a real tachometer that I can use to confirm the readings on the Arduino board.  So far, I have been pleased with the nifty all-in-one development environment of the Arduino, but yes, these projects always take longer than planned.



The zener should prevent the comparator seeing anything more than +6.2V or less than -0.7V.  It is running off 8.3V and ground.  You are right, the data sheet indicates a maximum of -0.3V on the input, although I am expecting the pulses to be positive.



Thanks,

Jeff

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Tundra10

Joined: 14 Jun 2010
Posts: 102
Location: Scarborough, Ontario

Posted: Tue Jul 19, 2016 9:14 am Post subject: Re: Off Topic: Outboard Motor Tachometer

Charlie,



The Arduino is a requirement :-)

The boat already has a nice digital tach for the driver to use.  The Arduino board is going to automatically set the trim of the motor based on rpm.  The code is written, it just needs to be able to sense the rpms.



Very ingenious idea using the microphone jack as the input for a phone-based oscilloscope.  I will have to try that sometime, although for this project, an extension cord is probably faster, since the behavior of the phone-oscilloscope would need to be validated.



Thanks,



Jeff

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