Marine Engine Synchronizer guage

[Spendandfix]

Could someone share a simple circuit diagram to build a marine engine synchroniser indicator? I believe how it would work is to measure and compare the frequency from each engine ignition coil and use three LEDs to indicate whether the port engine is too slow, (left LED is lit) the starboard engine is too slow (right LED is lit), or both are matched (center LED is lit.)

I have very limited experience with electronics, but am capable of building a simple circuit if one is available. I just purchased an Arduino beginners kit to strat playing around.

Thanks.

Jim

 

[danadak]

Use a block language to measure RPM and control the leds.

Snap4Arduino, Scratch, mBlock, Flowcode, Visuino, NODERED just a few to consider.

Here is a first pass at design.

Regards, Dana.

 

[ZipZapOuch]

Post #11 in the following thread gives a good general description of the accessing the hardware timers and counters in an Arduino (with ATmega328P based MCU).

Using the hardware counter in Arduino

Yes. But It blocks other all processing code during measurement. I don't like the use of blocking code. Also, the input capture by the hardware timer is clearly accurate than that. And It doesn't block other processing during measurement.

forum.arduino.cc

There are several ways to approach (counting engine pulses in a given interval or timing the duration between engine pulses are most likely).

There are many more ways to go about this but I don't know your experience with programming, circuit design, interest in programming simplicity vs adding glue logic etc. in any case te link above is a good read and if you are totally lost, then some conversations can be had.

Also, are you counting gear teeth with a Hall effect sensor to get many pulses per revolution or spark plug wire pulses on a single plug which results in a much lower resolution - the answer to that will determine the best strategy to approach the task.

Also, what time frame do you want to measure and what range is close enough (within 1%, within 1 rpm, within...?). With that, what resolution can you control the rpm?

Finally, you can train your ears with a pair of signal generators to understand what two synchronized engines sound like and hearing the beat frequency. And how that beat frequency goes up as the plane or boat accelerates (because a 1% error is many more beats/second at running speed than at idle).

 

[crutschow]

You would want to allow some small degree of mismatch in the two engine speeds for the center LED to light, as the two will never exactly stay the same.

My preference for such an indicator is a center-zero analog meter.
It readily shows the degree of mismatch and when they are synchronized.
The Arduino could be programmed to generate the desired analog voltages for the meter.

 

[danadak]

Pulsein accuracy in this application maybe a non issue. 6000 rpm
is ~ 160 uS, so error < ~1 %......

Depends on OP goal for accuracy.

Pulsin Accuracy on UNO 3.0

1/147th is 0.68%, not 6.8%. For values up to 146 there will be no correction except adding 1. I don't see how that helps with measurements down to 20 us. The UNO uses a ceramic resonator instead of a crystal. Still, I would expect it to be better than 0.68% accurate. The resolution of...

forum.arduino.cc

The blocking code issue in this design may also be a non issue, unless OP
is doing a lot more tasks/activities with board. Especially if interrupts
get turned off for some other reason. That would be a big issue if tied to
safety for man-machine viability, or in a control loop, eg. excessive latency,
error.

If high accuracy needed across the RPM range then traditional mix of gated freq counter
design for the high RPM range coupled with a reciprocal counter for low end would be easy
to achieve. I would use a PSOC for that case as it has ability to do all this in HW as well as
significant analog capability. In fact this range of freq possible to do it with a reciprocal
counter for entire range due to high counter clock rate and size in these parts.


Regards, Dana.

 

[Spendandfix]

Wow! Thank you all for your great responses. This is wonderful. I have always wanted to learn more about electronics. (I'm an old Mechanical Engineer.) But what you are sharing is way over my head. I don't want to take advantage of anyone, but I'll ask anyway. What I need is a circuit diagram and the Arduino code. I have searched the internet for such a thing without success, so I wondered if an electronics forum might provide it. This is the first one I joined. Specific to the design, I like the idea of a center gauge that could accommodate the small degree of mismatch that crutschow mentions. However, using LEDs may make for a simple, compact display design. A boating friend has one with LEDs so I assume that the circuit design manages this mismatch some how. If I recall correctly, the LEDs vary in brightness. (There are off-the-shelf gauges, but I'd rather build one if possible, as part of my learning process.) FYI - typical tachometer take a signal from the ignition coil. (not the spark plug lead but rather the supply voltage lead). I don't know how that works or what the signal looks like. I will read the recommended links to learn more.

Thanks again everyone.

Cheers,

Jim

 

[danadak]

If you wanted to control brightness of LEDs use a PWM to drive them
and the value to write (which controls its duty cycle, hence time LED is
on versus off) which could be a f(RPM difference).

I f you write a 0 to PWM its off, a 255 (all bits set for an 8 bit PWM).
In other words it can act both as a simple on/off pin or a controlled
duty cycle pin for values in between. Pin will have multiple functionality.

https://cdn.sparkfun.com/assets/resources/4/4/PWM_output_Arduino.pdf

The block language has a PWM block.



Regards, Dana.