[night0wl]

Hi all,

So I recently ordered a Raspberry Pi and more associated small equipment to make myself a NMEA wireless bridge/repeater. The plan is to (based on a recent Panbo article) utilize a Win8.1 cheapo tablet to run OpenCPN. I've already run the instrumentation and had it all working on my laptop at the helm, and even had OpenCPN acting as a TCP server....so this is no challenge.

*HOWEVER*, this project got me thinking. My Yanmar 3ym30 has only the idiot lights for water temperature, voltage, and oil pressure. At various stages, I've thought about upgrading the Yanmar Panel ($1000+ all in), buying the Maretron N2k instrument andharness ($700 all in), and the cheapest option, splicing in to the existing wiring and putting in analogy instrument gauges.

Then, I thought, hey, I have the raspberry pi. Why not use an arduino board to tap this data this way!?

The trouble is, I'm not very well versed with arduino and instrumentation. However, if I'm willing and able to fund the hardware purchase(s), is there anyone that can guide me through the project? The best thread I've got is this as a reference: Boat Digital Guage Project - Arduino Forum

I figure I'd start with a simple question...so here goes:

Q1 - can someone tap into existing idiot light gauges (at the sender or at the panel) in order to splice the data? How does one interpret the values being returned by the sender gauges (assuming they return various voltages or resistances back to the idiot lights helmide).

 

[miatapaul]

I would think you would need new senders but that should not be expensive as you can use standard ones the idiot lights are controlled by sensors that trigger a signal a to a point not a continuous range. Put in t fittings to keep existing sensors.

Look like a fun project. I doubt you will save money. But will have fun.

Sent from my NookColor using Tapatalk

 

[night0wl]

I would think you would need new senders but that should not be expensive as you can use standard ones the idiot lights are controlled by sensors that trigger a signal a to a point not a continuous range. Put in t fittings to keep existing sensors.

Look like a fun project. I doubt you will save money. But will have fun.

Sent from my NookColor using Tapatalk

THanks for the feedback!

Can you point to t-fittings that i can use for my senders? Im particularly interested in my oil pressure one?

I'm curious as to the need for new senders. The Maretron unit has a yanmar wiring harness that apparently ties directly into existing senders on my 3ym30 engine. So while they may be hooked up to idiot lights right now, it makes me think that if the Maretron is able to bridge them to NMEA 2000, I should be able to bridge them to plain ol NMEA....right?

Also, I think youre right about saving money, but this is a learning excercise too. Just for reference sake, the cheapest nmea wifi repeaters I've seen are upwards of $350. I'm less than $100 in for my diy one so far. That included the pi, a dc-dc step down/step up, a mini usb hub, a dc power brick to tap into the 12v supply...and misc bits and bots (case, cables). This commodity hardware stuff is amazing.

 

[night0wl]

I would think you would need new senders but that should not be expensive as you can use standard ones the idiot lights are controlled by sensors that trigger a signal a to a point not a continuous range. Put in t fittings to keep existing sensors.

Look like a fun project. I doubt you will save money. But will have fun.

Sent from my NookColor using Tapatalk

Whoops! Looks like you're right about the senders being limit. Here is an example of what someone did to "tee" in a coolant temp gauge.

Wonder how I would do this for oil pressure.

 

[eherlihy]

Whoops! Looks like you're right about the senders being limit. Here is an example of what someone did to "tee" in a coolant temp gauge.

Wonder how I would do this for oil pressure.

You will need a T and a nipple.

Locate the oil pressure limit switch. Unscrew it from the engine block. Thread a nipple to extend the oil pressure "gallery" to a more convenient location. Thread the "T" onto the nipple. Install the oil pressure limit switch, and the oil pressure sender (which is a potentiometer/varistor/rheostat).

On my vessel, instead of a nipple, the PO used a 2 foot length of high pressure hose. He mounted the senders away from the engine, on a bulkhead.
Here is a pic of the boat (when I first inspected her).

You can see next to the old battery charger (long since gone) the hose, the "T" and both senders (one of which is behind the raw water hose, above the mixing elbow).

 

[night0wl]

You will need a T and a nipple.

Locate the oil pressure limit switch. Unscrew it from the engine block. Thread a nipple to extend the oil pressure "gallery" to a more convenient location. Thread the "T" onto the nipple. Install the oil pressure limit switch, and the oil pressure sender (which is a potentiometer/varistor/rheostat).

On my vessel, instead of a nipple, the PO used a 2 foot length of high pressure hose. He mounted the senders away from the engine, on a bulkhead.
Here is a pic of the boat (when I first inspected her).

You can see next to the old battery charger (long since gone) the hose, the "T" and both senders (one of which is behind the raw water hose, above the mixing elbow).

Is there any impact to having the oil pressure be "teed" or on a hose further away from the engine block itself? Or does it even out across the entirety of the measurement surface?

 

[WoobaGooba]

How/where is the NMEA 2K decoding being done? OpenCPN able to decode 2K? 2K first converted to 0183 by? etc. Thanks.

 

[miatapaul]

Look at Summit Racing they have lots of generic gage and sending units.

Sent from my ADR6425LVW using Tapatalk

 

[night0wl]

How/where is the NMEA 2K decoding being done? OpenCPN able to decode 2K? 2K first converted to 0183 by? etc. Thanks.

The Maretron units are pure N2k. Just saying that if Maretron is able to take analog senders from Yanmar and convert to a digital signal....we should be able to do the same.

 

[-OvO-]

"Is there any impact to having the oil pressure be "teed" or on a hose further away from the engine block itself? "

No. It's a hydraulic system - pressure is the same everywhere.

 

[WoobaGooba]

Still not clear on what you are trying to do. An analog sensor to NMEA 0183 converter? Or an analog sensor to NMEA 2000 converter? If the later, how do you intend to obtain the NMEA 2000 protocol spec information?

 

[hellosailor]

nightOwl, you might want to read up on some of those systems and see what gearheads have traditionally done in cars.

A true "sender" for an idiot light may actually be a simple SWITCH. You can't convert that into a resistance-based sender, which typically changes resistance from roughly 0-240 ohms. So you need to find out what is on the engine and confirm what resistance range it is, or what range your replacement will be, and calibrate with it.

Extending or t-ing oil lines is also problematic. More lines, more fittings, and especially t's, tend to give you more oil leaks followed by total loss of oil pressure, a messy problem. That's why electric senders are considered the way to go, with no t's.

yes, you can kludge almost anything but you've got two distinct projects to sort out. One being the "simple" analog-to-digital conversion and display. The other being how to wire up sensors on an engine.

 

[night0wl]

Still not clear on what you are trying to do. An analog sensor to NMEA 0183 converter? Or an analog sensor to NMEA 2000 converter? If the later, how do you intend to obtain the NMEA 2000 protocol spec information?

Here are my goals.

1 - true sensors that aren't simple idiot lights/buzzer
2 - sensor should send the data not to the helm, but utilizing arduino to the raspberry pi
3 - raspberry pi should (via kplex) route data to boats wifi network.

This would allow me to use my Win81 tablet to see engine sensors data along with other instrumented data (wind, depth, ais) on a tablet.

 

[night0wl]

So, update on this project. Hit a stumbling block in the most unexpected place. Oddly enough, AIS when plugged into the Pi repeats over wifi...but *NOT* when directly plugged into my macbook (com issue???). Even stranger, nmea instruments plug into the macbook and display just fine...but WONT when I plug them into the pi. FRUSTRATING!

This picture shows AIS coming via wifi, but NMEA0183 still had to be plugged into the laptop.

Back to the engine instruments.

Yes, I agree..."teeing" into oil pressure seems risky. However how else would preserver the idiot light sender (already there) and then add the proper analog sender for true pressure readings?

 

[night0wl]

Well - I think I figured out why the data isn't flowing for NMEA. Tore the whole aft cabin apart to get to the Raymarine NMEA interface box. After plugging the pi directly into the box (you should see the ghetto setup...Ryobi 18v battery, dc-dc converter, alligator clips, a zip tie), I was able to see NMEA data flowing to the Pi.

Apparently, the USB cable is too long for the Pi to power. I was afraid of this when I ordered my equipment because a marinized USB hub is $50....half the project cost! Was hoping to squeak by with a passive USB hub, but no dice.

So, another trip to Amazon and this project will be continued *NEXT* weekend. Now, back to my dayjob

*edit*
a pic of the ghetto temporary setup. Notice the amazon box housing the dc-dc converter and the 18v ryobi battery powerpack!

 

[Alex W]

There are a lot of DC to DC power supplies available for under $10. I'm using this one for my Netduino-based wind instrument:
Amazon.com: Retailstore 2PCS LM2596 Buck DC-DC Adjustable Step Down Power Supply Module Converter New: Computers & [email protected]@[email protected]@http://ecx.images-amazon.com/images/I/[email protected]@[email protected]@51KgMaHYhnL

It works for me, but there are tons of other options to select from as well.

 

[night0wl]

There are a lot of DC to DC power supplies available for under $10. I'm using this one for my Netduino-based wind instrument:
Amazon.com: Retailstore 2PCS LM2596 Buck DC-DC Adjustable Step Down Power Supply Module Converter New: Computers & Accessories

It works for me, but there are tons of other options to select from as well.

Yep, I considered this one, but chose Amazon.com: DC-DC Converter Module Step up and down In 3.5-28V Out 1.25-26V Adjustable (LM2596S+LM2577S): Car [email protected]@[email protected]@http://ecx.images-amazon.com/images/I/[email protected]@[email protected]@51TUFeoGSrL . Simply put, I wanted the input voltage to always be 12v. Sometimes boat batteries can drop below that due to discharge, so I wanted the ability of the Pi to keep running. Those step downs wont work in that situation.

 

[capecodda]

I've built some simple things out of Arduino. Looks like from a brief search the Raspberry Pi system doesn't have an on board A/D converter, but people have built them and there maybe some kits.

If you have analog sensors for things like oil pressure, I don't see why you couldn't design a high impedance interface that would just go in parallel across the sensor with whatever gauge you got to measure a voltage level without impacting the gauge. Then you could infer a resistance level and translate in code to an oil pressure for example.

I've never really dug into the NEMA stuff, so no help there.

Warning, every time I start messing with some hack like this, it's more work than originally planned Best of luck.

 

[Alex W]

Simply put, I wanted the input voltage to always be 12v. Sometimes boat batteries can drop below that due to discharge, so I wanted the ability of the Pi to keep running. Those step downs wont work in that situation.

I thought that the Pi could run on 5V, but didn't look closely at it. My Netduino wants 7-10V ideally, so a step-down only power supply was more than adequate.

 

[night0wl]

I thought that the Pi could run on 5V, but didn't look closely at it. My Netduino wants 7-10V ideally, so a step-down only power supply was more than adequate.

You know you're right. But I dont have the pi hardwired. It goes through a 12v -5v brick...or through a usb hub which takes in 12v. Just wanted the 12v to be steady.