How to output GPS signal to a DSC radio?

[sdowney717]

Originally Posted by Moo

Another look at the suppliers site shows that the PPS version of this device uses two black wires but the one in question should only use the one on pin 1. So the black wire from pin 1 of the GPS should go to black of the radio.. Looks like you have used the shield too. The shield should be connected to ground only at one end of the cable (to prevent ground loops) so disconnect the GPS and using your multi-meter check for continuity between shield and black. If there is continuity do not connect shield to anything at your joint. If there is no continuity connect shield and black together.

Shield wire and little black wire have less than an ohm between them.

[sdowney717]

Originally Posted by Moo

Another look at the suppliers site shows that the PPS version of this device uses two black wires but the one in question should only use the one on pin 1. So the black wire from pin 1 of the GPS should go to black of the radio.. Looks like you have used the shield too. The shield should be connected to ground only at one end of the cable (to prevent ground loops) so disconnect the GPS and using your multi-meter check for continuity between shield and black. If there is continuity do not connect shield to anything at your joint. If there is no continuity connect shield and black together.

Ok, there is continuity between them, so I will disconnect the shield back wire at the radio and just use the little black wire.
In the description it does at the top say the baud is set to 4800, but further down says set to 9600, but I think its really 4800, that is the common one. 'but yes their listing lists both as the default.

The solder joints just temporary, just to see if it can work.
Radio is brand new.
I will do that disconnect shield tomorrow and report back.

[GILow]

Originally Posted by sdowney717

1.5 seconds is cold start time.

12vdc is the supplied voltage.

Even after 10 minutes nothing.

I have seen it work after a second, 45 seconds, 1.5 minutes or never at all.

GPS is being powered on as radio turns on.

1.5 second cold start time for a GPS is a new one to me.

[sdowney717]

https://www.ebay.com/itm/RS422-RS485...kAAOSwcLxYDBj1

This is a converter for $6. If disconnect shield and no help,
then buy this and try it?
I am assuming radio side would use TX- and Tx+ to the radio black and red input of the miniplug?

[sdowney717]

Originally Posted by GILow

1.5 second cold start time for a GPS is a new one to me.

Listing says this
Time To First Fix
Hot start 1.5 sec
Cold start Autonomous36 sec

Is cold start for when its not ever been on for a long time and the satellite map in its head needs updating?

https://www.aliexpress.com/item/3291...74084c4d31yNQm

I paid $17 for mine, seller has knocked it down a lot, wonder why. Cause they dont work?

[CarinaPDX]

Originally Posted by sdowney717

https://www.ebay.com/itm/RS422-RS485...kAAOSwcLxYDBj1

This is a converter for $6. If disconnect shield and no help,
then buy this and try it?
I am assuming radio side would use TX- and Tx+ to the radio black and red input of the miniplug?

That is just a breakout board, not an RS-232 to RS-422 converter.

Yes, the TX+ would go to the radio's red wire, and the TX- to the radio's black wire (both on the supplied pigtail).

Greg

[CarinaPDX]

The reason the price is so low is that the market has moved on to combined GPS/GLONASS receivers, and GPS/GLONASS/BeiDou receivers and even GPS/GLONASS/BeiDou/Galileo receivers (but only 3 of the 4 at one time). The 4-system unit similar to yours is less than $30 - they are all pretty inexpensive.

A cold start is when the GPS has either been off long enough that the satellite ephemeris previously downloaded is out of date, or the GPS has been moved to a distant location where different satellites are used. The extra time over a hot start is for downloading the current ephemeris data for the satellites in view. The GPS receiver has to wait for the broadcast, so that is the limiting factor - about half a minute is as fast as you will find.

It is very common for the Chinese to just copy a page of description and specs for similar products, and not pay attention to the details. The top entry specifically states the defaults, and that is usually the controlling statement. Baud rate is not your problem... It is most likely associated with ground; the question is really whether you can solve the problem by reconfiguring the ground, or will have to do a proper conversion.

Greg

[sdowney717]

Originally Posted by CarinaPDX

That is just a breakout board, not an RS-232 to RS-422 converter.

Yes, the TX+ would go to the radio's red wire, and the TX- to the radio's black wire (both on the supplied pigtail).

Greg

ok
So how bout these 2
First one does not mention 422, but does say 485
https://www.ebay.com/itm/DTECH-RS232....c100005.m1851

https://www.ebay.com/itm/RS-232-RS23....c100009.m1982

[GILow]

Originally Posted by sdowney717

Listing says this
Time To First Fix
Hot start 1.5 sec
Cold start Autonomous36 sec

Is cold start for when its not ever been on for a long time and the satellite map in its head needs updating?

https://www.aliexpress.com/item/3291...74084c4d31yNQm

I paid $17 for mine, seller has knocked it down a lot, wonder why. Cause they dont work?

Those numbers make more sense. Cold start time is still very good, but 1.5 seconds would have been impossible, I think. Your description of the satellite map in its head is not a bad description.

But anyway, it has ruled out my initial theory, which was that the delay was simply the device getting its gps fix.

Good luck getting it going. You’re in good hands here, plenty of good ideas coming through.

I’m interfacing my M5stack with my Icom 802 to get a GPS fix when I get a chance, and I think some of the stuff posted here might help me when I tackle that project.

[CarinaPDX]

Stick to 422 converters - often converters can do both 422 and 485, but these are different standards and unless they say 422 you can't count on it working. The second one looks fine; you would hook up the radio's pigtail to the terminals on the breakout board, then solder a male DB9 (actually DE9) connector to the GPS and plug it into the converter. Or you can buy another breakout board, with the opposite gender to the one included, similar to this: https://www.ebay.com/itm/1Pc-RS232-T...L/113646385166 . Both this and the converter come from China so be patient about 6 weeks...

Greg

[sdowney717]

Originally Posted by CarinaPDX

Stick to 422 converters - often converters can do both 422 and 485, but these are different standards and unless they say 422 you can't count on it working. The second one looks fine; you would hook up the radio's pigtail to the terminals on the breakout board, then solder a male DB9 (actually DE9) connector to the GPS and plug it into the converter. Or you can buy another breakout board, with the opposite gender to the one included, similar to this: https://www.ebay.com/itm/1Pc-RS232-T...L/113646385166 . Both this and the converter come from China so be patient about 6 weeks...

Greg

ok, thanks. I likely have a male serial plug, have lots of old cables and connectors from really old AT PC's
I am thinking will take 2 pins from gps, and was pin 1 ground and 3 or 5?

This one might be quicker shipping.

https://www.ebay.com/itm/New-Serial-...kAAMXQH-pRCJbH

and it says this, does it mean it may not need power to work? which i doubt for my app.

This converter is compatible with RS-232C,RS-485,RS-422 standard ,enable transfer RS232 Signals to Balance Difference RS485 or RS422 signal.
Converter can extends RS232's transmission distance to 1.2KM, drive by using special RS232 charge pump without external power, get power withoutinitialized RS

[CarinaPDX]

That one is shipped from China, so very slow delivery. Consider this one: https://www.ebay.com/itm/DTECH-RS232...i/163649374032 . A bit more expensive but at least you will get it before summer's end.

RS-232 outputs at higher voltage and power (usually) than RS-422, so this circuit is using some of that higher 232 power to drive the circuit. Since all of the communication is coming from 232, and none going to 232, there should be plenty of power. Pin 1 is for the shield, not the signal ground. The signal ground is on pin 5. I think the TX signal should go to pin 2, but if not 3 (I'm too tired at the moment to try to sort out which it is, but trial and error works).

As for the ground situation, the GPS documentation is too lacking to be certain. Basically there are three grounds: signal ground, power supply ground, and shield ground. Ideally the device would provide separate signal and power supply grounds, and as noted earlier the shield should be connected on one end only. There are only 2 ground wires shown - the larger one towards the bottom of the photo appears to be the shield ground; if you strip off the heat shrink you should be able to see if there is another insulated wire besides the shield braid and/or un-insulated shield wire. If it is only the shield then the power supply ground would need to be connected to the other black wire. If there is another insulated wire connected to the shield it would likely be the power supply ground and likely you are best off as is - and then an adapter would be the next step. [Edit: my earlier recommendation to short the two black wires together was to check if the power supply negative needed to be connected to the other wire.]

Greg

[sdowney717]

Originally Posted by CarinaPDX

That one is shipped from China, so very slow delivery. Consider this one: https://www.ebay.com/itm/DTECH-RS232...i/163649374032 . A bit more expensive but at least you will get it before summer's end.

RS-232 outputs at higher voltage and power (usually) than RS-422, so this circuit is using some of that higher 232 power to drive the circuit. Since all of the communication is coming from 232, and none going to 232, there should be plenty of power. Pin 1 is for the shield, not the signal ground. The signal ground is on pin 5. I think the TX signal should go to pin 2, but if not 3 (I'm too tired at the moment to try to sort out which it is, but trial and error works).

As for the ground situation, the GPS documentation is too lacking to be certain. Basically there are three grounds: signal ground, power supply ground, and shield ground. Ideally the device would provide separate signal and power supply grounds, and as noted earlier the shield should be connected on one end only. There are only 2 ground wires shown - the larger one towards the bottom of the photo appears to be the shield ground; if you strip off the heat shrink you should be able to see if there is another insulated wire besides the shield braid and/or un-insulated shield wire. If it is only the shield then the power supply ground would need to be connected to the other black wire. If there is another insulated wire connected to the shield it would likely be the power supply ground and likely you are best off as is - and then an adapter would be the next step. [Edit: my earlier recommendation to short the two black wires together was to check if the power supply negative needed to be connected to the other wire.]

Greg

Yes, the thicker black wire is the shield of the cable.

If I need this converter, should the GPS shield wire then go to pin 1?
And If I do hookup the 12v power to the converter it will still work?
I was thinking it is a convenient spot to power the GPS red wire and black wire from.

So the small non shield black wire coming from GPS is not connected to any pins, just the negative connection on the other side of the converter next to the 12v positive?

I suppose I am starting to understand how this thing will work, so there is some hope afterall. I suppose I should have tried to buy a marine rs422 gps, if they make such a thing , but this one is cheap. As long as I can make it work, It will be worth the effort of learning how.

[CarinaPDX]

Let's talk about the adapter when/if it comes to that.

It is clear that the lower (in the photo) black wire is attached to the shield; the question is whether it is only the shield or is there another insulated wire connected to the shield under the heat shrink. If it is only a shield connection then the 12V- power supply must be connected to the other black wire, otherwise the power supply ground is conducting through the shield which can be expected to cause problems - the sort you have been experiencing. That is your assignment for tomorrow

Greg

[CarinaPDX]

Originally Posted by sdowney717

I suppose I should have tried to buy a marine rs422 gps, if they make such a thing , but this one is cheap. As long as I can make it work, It will be worth the effort of learning how.

There's the rub: I have seen a lot of these cheap Chinese GPS units, but none with a proper RS-422 interface. The GPS modules inside usually contain several interfaces, including a UART, USB, SPI, and I2C. The UART outputs the signal in the RS-232 and RS-422 format, but at logic voltage levels: an external drive circuit is needed. The GPS you have has a 12V to 5V converter, to power the system, and a 3.3V or 5V to 12V drive circuit.for the UART to provide RS-232 signals. It wouldn't be difficult at all to instead drive a differential 5V RS-422 signal. The truth is that the market for RS-232 GPS units is small, and market for the RS-422 units is miniscule. The marine market is small to begin with, but within that the need for separate receivers is tiny - we aren't that important. The market for drone GPS units, using SPI or I2C interfaces, is probably much larger. So we adapt...

Greg