Anchor Watch Software

Terry Cox · May 15, 2017

Hi Ralph, the diagram that you posted was very helpful. Thank you.

Do you know what type of alarm signal the Garmin 178C outputs through the yellow lead? Assuming it is electrical as opposed to digital. My manual is on the boat and am working on a relay solution, but need to know the output. Is it the 100mA that you reference?

Ralph Johnstone said:
Your Garmin 178C is similar to my Garmin GPSMAP 2006 in that they both have a takeoff for a 100 mA load to power an alarm. This allows you to insert a relay with a small coil (about10-20 mA) and then the sky's the limit for loading.

Terry Cox · May 15, 2017

Ralph Johnstone said:
Doubtful, as this is not a boating item but rather an electronics item. If you have an electronics store near you, just ask for a 10 A relay with a 12 VDC coil. The coil draw should be very low but just ensure that it's less than the rated 100 mA of the GPSMAP 178C. For mounting the relay and any other other items, use a breadboard and enclose the whole thing in a plastic electronics box. If the sales people are electronics nerds, take a drawing with you and they'll sell you everything you need.

Hi Ralph, the relay that should work is here: http://www.diytrade.com/china/pd/12..._SL_B_SRU_12VDC_SL_C_SRU_24VDC_SRU_48VDC.html

PN is : SRU-12VDC-SD-C

Also trying to figure out the connections to make it work. Almost there, but do need to know the alarm output. Thanks in advance for your help.

Ralph Johnstone · May 15, 2017

Terry Cox said:
but do need to know the alarm output.

Hi Terry. The alarm circuit in the chart plotter has no output but behaves like a switch with either an OPEN position which means you're within the desired radius of you anchor or a CLOSED position which sets off the alarm bells because you're beyond the desired radius of your anchor. That switch is very delicate and can only handle 100 mA max. You have to provide the power to go through that plotter switch and into the relay coil. The coil then closes the relay contacts which will handle the larger 2-3 amp power supply to the alarm.

Wish I could see the top of that relay but it looks like it's 24 VDC which I doubt will work. It would really be easier if you could find an electronics outlet near you. I don't know why but there's one corner here in Burnaby which has three of these electronics outlets. Weird.

What we don't know is what is the electrical demand of the coil in the relay. They're usually very small but if you've got a multimeter (which you must a a DIY boater) try it out on the bench and see what the coil takes at 12 VDC. Probably far less that the rated 100 mA. But having said that, it would be a good idea to insert a 0.100A fuse in the circuit to protect the alarm switch in the plotter. According to what I can make out on the top of the relay, the contacts are good for any alarm load you will be demanding.

Terry Cox · May 15, 2017

Ralph Johnstone said:
Wish I could see the top of that relay but it looks like it's 24 VDC which I doubt will work.

Hi Ralph, purchased the 12VDC relay from Vetco, a local electronics store, so it should work? I'm just trying to figure out how to hook it up. The 178C diagram shows a relay that is needed to make deliver the amps to the alarm. Vetco just needs to know how much DC the GPS is sending through that yellow alarm wire that is to connect to the coil in order to cause the relay to switch.

Ralph Johnstone · May 15, 2017

If you look at my previous diagram:

look where your 12VDC battery (bank) is sitting. Take a (+) connection from there and run it to one side of the coil in the relay and the other side of the coil goes to the yellow alarm wire. Remember this is purely schematic but the (+) should be on the same circuit as your GPS. Once the (+) current enters the GPS, it will find its own way to the (-) side. Don't worry about what goes on in there.

The amperage is controlled by I = E/R (Ohm's Law's). E is always 12V and the R is the resistance of the coil. Just to satisfy yourself with whats happening, measure the resistance of the coil to see if the amperage to GPS is less than 0.100 A using Ohm's Law

Terry Cox · May 15, 2017

Hi Ralph, thank you for your input. In the attached schematic,

how would you hook them up?

Ralph Johnstone · May 15, 2017

Remember this is a schematic. Your power supply comes from the (+) terminal on your GPS breaker. Don't run it from the battery. Protect the GPS internal switch with a 0.100A fuse. The same wire can continue on through the normally open switch in the relay to provide (+) power to the bell. The GPS breaker will protect the new wire from an overload. Your installed GPS already has a ground in it, so don't concern yourself with it. The solenoid coil circuit is now complete.

The ground wire from the bell will go back to the (-) bus bar in your panel. And you're finished.

I hope you complete this before Wednesday because I'm leaving for Nevada on May 17 to learn how to drive a steam locomotive. Figured it's about time I learned a useful occupation. And it certainly can't be any more expensive than owning a boat.

JamesG161 · May 16, 2017

Ralph Johnstone said:
learn how to drive a steam locomotive.

Just remember to pick the right crew and not to make your own Course.

Jim...

Ralph Johnstone · May 16, 2017

JamesG161 said:
Just remember to pick the right crew and not to make your own Course.

OMG ..................... there goes my damage deposit

! ! ! ! !

Terry Cox · May 16, 2017

Ralph Johnstone said:
I hope you complete this before Wednesday because I'm leaving for Nevada on May 17 to learn how to drive a steam locomotive. Figured it's about time I learned a useful occupation. And it certainly can't be any more expensive than owning a boat.

Thanks for your help Ralph. Will you learn on a Mallet? I hope, I hope, I hope.

A couple of question:
1. Scoured the 178C manual and could find no reference to the alarm output current from the GPS. I'm assuming that it is not digital, but it would seem to me that the coil will need some sort of current to drive the switch.
2. No need to use the relay common for any reason?

Ralph Johnstone · May 16, 2017

Glad to be of help and it'll be great to see this thing work.

What your GPS does not do with that yellow wire, is put out current to the alarm, or anything else. It only acts as a switch and it's either OPEN:

and no current flows because there is nothing there to conduct the current or it's CLOSED:

and the current which YOU supplied (in your diagram) flows because there is now a conductor in between the contacts. You have to supply the current to energize the coil by installing new wiring from your GPS breaker .

For your second question, the relay common contact is on the switching side of the relay and you will attach one wire of the new alarm supply to this common contact and the other wire will go to the "normally open" contact. In this way, when the coil receives electricity, it energizes and becomes magnetic. This magnetism is what pulls the relay contacts together and allow current to flow to the alarm.

Without my being there, maybe it would be easier for you to photograph the following parts and send them to me. I'll arrange them showing the used contacts to illustrate exactly how it goes. PM me as it's easier than trying to draw on here:

Photos to supply:
The relay from several different angles showing any diagrams it may have imprinted on the side.
The alarm device you plan to use.
The rear of your GPS supply breaker located behind your electrical panel.
The yellow wire coming from your GPS where you can electrically connect to it.

Terry Cox · May 17, 2017

Ralph Johnstone said:
Photos to supply:
The relay from several different angles showing any diagrams it may have imprinted on the side.
The alarm device you plan to use.
The rear of your GPS supply breaker located behind your electrical panel.
The yellow wire coming from your GPS where you can electrically connect to it.

Hi Ralph, thanks again. Regarding any photos:
1. The relay has zero diagrams imprinted on the side.
2. Standard 12vDC door alarm. Device is on the boat, so a few days before a photo.
3. Ditto the GPS supply breaker, but if I recall it is a standard Paneltronics 15amp breaker.
4. Ditto the yellow wire from the GPS, which is also on the boat.