Converting 12v alternator signal to HIGH/LOW into a uController with an opto-isolator

Thread Starter

ba58smith

Joined Nov 18, 2018
62
I just re-read the entire thread. You mention a ESP8266 wi-fi microchip but you do not show it in any of your diagrams. How is it connected?

I have one of those. It works very well for the price. Here are the instructions for adjusting the DC offset. It's under Operations / Vpos Alignment.
View attachment 176803
Keith, I do show the ESP8266 in all of the schematics. It's the Wemos D1 Mini, and it's connected as shown.

I have the instructions for the DS0138, but when I read them, they didn't make any sense to me, in part because I've never used an oscilloscope before so I didn't know about setting the ground level, and in part because they were written by someone who doesn't write very clear documentation. :) I've finally watched enough videos, and pushed the buttons enough times, to have figured that out on my own. I think I'll make my own video, and document the whole process of using the DSO138, because it's probably being bought by a lot of people like me who need much better instructions than what's currently available.
 

masterov

Joined Oct 22, 2020
3
Hey ba58smith,

I found this thread because I am trying to something very similar: connect the tach wire from balmar mc-614 to a raspberry pi.

I am curious why you decided to use an optocoupler? Do you think I can connect the wire directly to GPIO pin through a voltage divider?

Thanks,
A.
 

Thread Starter

ba58smith

Joined Nov 18, 2018
62
Hey ba58smith,

I found this thread because I am trying to something very similar: connect the tach wire from balmar mc-614 to a raspberry pi.

I am curious why you decided to use an optocoupler? Do you think I can connect the wire directly to GPIO pin through a voltage divider?

Thanks,
A.
Because the signal coming from the Balmar is VERY noisy. If you look at it on an oscilloscope (which I did), you can see that it's generally an up/down wave, but there are major spikes on the uphill and downhill slopes of every wave, and they're big enough to be counted by the GPIO pin as separate on/off events.

I finally gave up, because I could never get the signal completely clean, and my measured RPM would be higher and higher than actual as the RPM increased. However, someone else took the same general idea, then made it better with some more capacitors and other things, and he says it works great. See his schematic, attached.

And if you're not sure how you're going to view the results on your boat, check out www.signalk.org, and the sub-project https://github.com/SignalK/SensESP. It's going through a real dev spurt right now, and is being discussed in the #sensors channel on signalk-dev.slack.com.
 

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mattmgame

Joined Feb 1, 2021
1
Because the signal coming from the Balmar is VERY noisy. If you look at it on an oscilloscope (which I did), you can see that it's generally an up/down wave, but there are major spikes on the uphill and downhill slopes of every wave, and they're big enough to be counted by the GPIO pin as separate on/off events.

I finally gave up, because I could never get the signal completely clean, and my measured RPM would be higher and higher than actual as the RPM increased. However, someone else took the same general idea, then made it better with some more capacitors and other things, and he says it works great. See his schematic, attached.

And if you're not sure how you're going to view the results on your boat, check out www.signalk.org, and the sub-project https://github.com/SignalK/SensESP. It's going through a real dev spurt right now, and is being discussed in the #sensors channel on signalk-dev.slack.com.
@ba58smith
Hello, I spent a good around of time reading most of what you have done on this project. Not just in this thread. You wrote that you gave up, do you me you stopped working on it? Sounds like you were close.
I'm also trying to get my engine rpm from the alternator, on an old tractor I own, it had a tachometer that ran off the alternator before, I'm now trying to get it to work with an Arduino.
You attached a schematic in your last post, did you try getting the rpm using that schematic?
I'm having a hard time finding the schematic (and information about it) on the websites you noted in your post. Could you direct me to where you got it from.

Thanks, any help is much appreciated.
Matt
 

Thread Starter

ba58smith

Joined Nov 18, 2018
62
Matt,
You won't find that schematic on those websites. It was posted to a discussion on Slack by another guy using Signal K and SensESP. I haven't tested it, but I'm confident it works, based on my interactions with him on Slack. Give it a try! (But if all else fails, do what I did - epoxy several magnets around the edge of the harmonic balancer or some other spinning part on the engine, and read them with a Hall Effect Sensor. Works great!)
 
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