Homemade NMEA multiplexer

I am sorry if I have hurt your feelings by not admiring your project enough. I just feel it is strange that you go into technical argumentation as claiming the PIC is not capable to output NMEA acceptable levels without a lot of peripheral components and even go into details about it missing voltage levels to output RS422 and that RS232 is superior to RS422 with better fan out capability when you obviously don't have the knowledge about this to support your claims.

After you have realized that all your previous statements are wrong and have nothing more to say, you change into ridiculing everything instead. Go improve your design instead.

Again, I am sorry I didn't express the admiration you expected. But the £6 design you initially claimed seems to be a £20 ready made prototyping board with a very small extension to it? And I suspect the bit banging software UART you knocked up, in reality is just a free software library that you downloaded. Sorry if I am too sceptical, but when such a simple task as supplying an inverted signal to the hardware USART Tx pose a problem for you, I don't see why you would go into bit banging in PIC assembler when there are ready made routines available.

I think it is good that you experiment with the PIC and have fun with it and there is no problem with your project really. But I can't see why you are objecting and acting up in all possible ways just because I tell you there are improvements that can be made.

There are some easy tricks to do things, that you didn't seem to think of (like feeding the Tx line back to your PIC), that I think you should consider or at least remember for future designs, instead of just ridiculing everything when you are out of arguments.

Then I don't see why you stress facts like "newly arrived swedish" friend? Does it in any way make my argumentation weaker because I am swedish, or newly arrived, or what? Should I be ashamed of being swedish, or what is your purpose of pointing out this?

Why not calm down and stop ranting like that. You should be happy anyone is interested in your design efforts and spend time to comment on it, both positive and negative comments. And I really never made any negative comments. I just gave you suggestions for improvement (and making it cheaper, as that seemed to be a priority for you at first).
 
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I don't believe there is any malicious intent here - its just a British thing we have with guys in sheds.

A few years back I rebuilt my boat engine in my shed, never done anything like that before, no knowledge of diesel engines, and am not that sort of engineer.
If I costed my time it would have been cheaper to go and buy a brand new 4000L gold plated V12, but I was quite pleased even though it took all winter. I am sure even a inexperienced marine engineer would have rebuilt a single cylinder volvo in 10 minutes including a cup of tea, but thats not the point.

So I would be inclined not to take anything personally...not that its any of my businesss!!!
 
Ridax said:
I am sorry if I have hurt your feelings by not admiring your project enough. I just feel it is strange that you go into technical argumentation as claiming the PIC is not capable to output NMEA acceptable levels without a lot of peripheral components and even go into details about it missing voltage levels to output RS422 and that RS232 is superior to RS422 with better fan out capability when you obviously don't have the knowledge about this to support your claims.

After you have realized that all your previous statements are wrong and have nothing more to say, you change into ridiculing everything instead. Go improve your design instead.

Again, I am sorry I didn't express the admiration you expected. But the £6 design you initially claimed seems to be a £20 ready made prototyping board with a very small extension to it? And I suspect the bit banging software UART you knocked up, in reality is just a free software library that you downloaded. Sorry if I am too sceptical, but when such a simple task as supplying an inverted signal to the hardware USART Tx pose a problem for you, I don't see why you would go into bit banging in PIC assembler when there are ready made routines available.

I think it is good that you experiment with the PIC and have fun with it and there is no problem with your project really. But I can't see why you are objecting and acting up in all possible ways just because I tell you there are improvements that can be made.

There are some easy tricks to do things, that you didn't seem to think of (like feeding the Tx line back to your PIC), that I think you should consider or at least remember for future designs, instead of just ridiculing everything when you are out of arguments.

Then I don't see why you stress facts like "newly arrived swedish" friend? Does it in any way make my argumentation weaker because I am swedish, or newly arrived, or what? Should I be ashamed of being swedish, or what is your purpose of pointing out this?

Why not calm down and stop ranting like that. You should be happy anyone is interested in your design efforts and spend time to comment on it, both positive and negative comments. And I really never made any negative comments. I just gave you suggestions for improvement (and making it cheaper, as that seemed to be a priority for you at first).
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Wow!
 
AngusMcDoon said:
Do you think it's jolly bad form to dis another chap's software without having done a code review first? :)
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Doesn't seem to be in industry.
In fact very little software gets any respect at all, particularly from us hardware guys...

Although I have had the privilege of working with a few very, very good people over the years.
 
electrosys said:
There may be something of interest here for those with expertise :
http://www.shipmodul.com/en/connections.html
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Nice, simple description and diagrams. Thanks for the link.

There are nmea-to-PC serial port isolators available. These provide galvanic isolation and signal level conversion so that the PC 'sees' the correct signal levels and doesn't zap the nmea interface. They're expensive, though. Maybe another cheap h/w project for someone this winter?
 
Rogershaw said:
Maxam do a chip that can provide RS232, RS422 and RS485 output levels. Don't know cost but could be a solution.
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The problem is not finding a solution. The problem is getting the OP to understand he needs it... :D He is happy connecting it all together without any isolation and even use RS232 Rx cirquits to read NMEA devices. AFAIK NMEA only (reluctantly) accepts RS232 levels as talkers, not as listening devices (and for a good reason too).

Instead of spending money/efforts/space on a max232 he should use that on 2 opto couplers instead.

There are two ways he could connect a NMEA talker through the max232. Either he use one of the NMEA data lines to tie to ground, which results in a data line being grounded (potentially unhealthy) or he takes ground (if he can find it) from the NMEA talker and tie it to ground on the max232. This will give him a 0/5V signal to the max232, while RS232 specifies it thresholds to be a -3/+3V. Not ideal, but electrically working because most RS232 circuits are forgiving. But wasn't a 0/5V signal for RS232 the very thing he objected to on his Tx and the reason he wanted the max232? So whatever he does, he violates the RS232 standard (as well as the NMEA standard).

"The great thing about standards is there are so many to choose from." (quoted from Maxim's WEB site) If OP research carefully, maybe he can find a standard that is exactly as he does it... :)
 
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Ridax said:
The problem is not finding a solution. The problem is getting the OP to understand he needs it... :D He is happy connecting it all together without any isolation and even use RS232 Rx cirquits to read NMEA devices. AFAIK NMEA only (reluctantly) accepts RS232 levels as talkers, not as listening devices (and for a good reason too).

Instead of spending money/efforts/space on a max232 he should use that on 2 opto couplers instead.

There are two ways he could connect a NMEA talker through the max232. Either he use one of the NMEA data lines to tie to ground, which results in a data line being grounded (potentially unhealthy) or he takes ground (if he can find it) from the NMEA talker and tie it to ground on the max232. This will give him a 0/5V signal to the max232, while RS232 specifies it thresholds to be a -3/+3V. Not ideal, but electrically working because most RS232 circuits are forgiving. But wasn't a 0/5V signal for RS232 the very thing he objected to on his Tx and the reason he wanted the max232? So whatever he does, he violates the RS232 standard (as well as the NMEA standard).
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Why should he HAVE to "understand"
You gave your point of view quite a long time ago. Why are you getting bent out of shape because he wont "understand"?
Stu
 
skipper_stu said:
Why should he HAVE to "understand"
You gave your point of view quite a long time ago. Why are you getting bent out of shape because he wont "understand"?
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And where did I say he HAVE to understand? I purely said the problem is getting him to understand and not in getting a correct solution... He can do whatever he wants as far as I am concerned. I wouldn't recommend any others to do what he does, but for HIM I totally RECOMMEND it. :) (Sorry, YOU are welcome to do it too, don't want you to feel left out. Why not lend him your equipment to test with ;) )
 
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skipper_stu said:
Why should he HAVE to "understand"
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Oh I've given up responding to the Swedish Tim Bartlett of the electronics world. I accept that he is a lot more knowledgeable than me, has good points to make, but when he got all upset about netiquette on my feeble attempt at humour with the addition to the airbus crash report, I couldn't take him seriously any more.

I'm looking for a good electronics forum where I can post about boats and sailing and stuff. Anyone know of one?
 
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Ridax said:
The problem is not finding a solution. The problem is getting the OP to understand he needs it... :D He is happy connecting it all together without any isolation and even use RS232 Rx cirquits to read NMEA devices.
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Hang about a bit ...

Let's review the context of this project. A bloke - who's not claiming to be an electronics expert - has got off his backside and has put together something which many 'experts' (I'm kinda including myself here) have got on their 'to do'/ 'one rainy day'/ 'must get around to making' list. Good on the bloke.
Then - because he's going to plug the gizmo into his serial port, he's not fitted any isolation, but has fitted an RS232 interface instead. Fair enough. If I was making such a device for myself and maybe a few mates, then I'd have done exactly the same.

Then the bloke generously posts about his project and is met with negative criticism more appropriate for someone who is about to start mass production.
The OP is quite clear about his intentions - he wrote, "My total cost reducing exercise is just a bit of theoretical fun. I'm not planning to start production."

Got it ? He's not planning to flood the market with Multiplexers which do not meet all of the NMEA specifications. He's put together something which meets his requirements.

I, for one, am rather hoping that the OP might release his project details into the public domain (BIG begging hint), as I'd like to build one ... complete with an RS232 interface !
 
electrosys said:
Hang about a bit ...

Let's review the context of this project. A bloke - who's not claiming to be an electronics expert - has got off his backside and has put together something which many 'experts' (I'm kinda including myself here) have got on their 'to do'/ 'one rainy day'/ 'must get around to making' list. Good on the bloke.
Then - because he's going to plug the gizmo into his serial port, he's not fitted any isolation, but has fitted an RS232 interface instead. Fair enough. If I was making such a device for myself and maybe a few mates, then I'd have done exactly the same.

Then the bloke generously posts about his project and is met with negative criticism more appropriate for someone who is about to start mass production.
The OP is quite clear about his intentions - he wrote, "My total cost reducing exercise is just a bit of theoretical fun. I'm not planning to start production."

Got it ? He's not planning to flood the market with Multiplexers which do not meet all of the NMEA specifications. He's put together something which meets his requirements.

I, for one, am rather hoping that the OP might release his project details into the public domain (BIG begging hint), as I'd like to build one ... complete with an RS232 interface !
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Hear hear...

It's like most things I do for my boat - I'm sure there are hundreds of better ways to do them, I just want something that does what I set out to do, which I can make with the tools and materials I have to hand... :o
 
I think this is great and it is what PBO is all about.

We must encourage this and any other projects like this.

If anyone wishes to make constructive suggestions OK but leave it at that. Don't start arguments if you disagree.

I have made several projects like this and have been reluctant publicize due to this kind of negative feedback.

We need more of this and would like PBO mag to maybe take up on some of these projects.
 
electrosys said:
I, for one, am rather hoping that the OP might release his project details into the public domain...
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Well when the electronic attack dog up their claimed that I hadn't written the code for the soft UART, I was going to post a whole load of C source.

But then I had a horrible premonition. That would just start the whole process again from the software engineers barking at me...'You should have done a shift instead of a divide' etc.

Maybe I should post details of the plastic box it sits in so the industrial designers can come in and have a chew :D.
 
electrosys said:
Then the bloke generously posts about his project and is met with negative criticism more appropriate for someone who is about to start mass production.
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This is where you go wrong... he was NOT met with negative criticism but he ACTED as if he was. Go back to page 1 and 2 and see what was so negative about my comments there? There was a discussion (not started by me) if he should be using max232 or max233 and then I simply suggested that the max232 is not necessary at all.

Below is a short transcript of how the conversation was. What was negative about that? But just because I pointed out that the max232 is not necessary and that rs422 is recommended, he starts to question this and make technical comments about my suggestion, that are just not correct and which I am sure he NOW can admit was not correct.

But just because of this he starts to rant about it and puts 232 all over the thread. My comments were in no way negative but rather helpful and on the subject, but he just couldn't accept it without arguing.

Ridax said:
Why use a 232 at all? NMEA is not RS232 level anyhow. So rather than saving 70p by changing to a less capable pic you could just skip the 232. If you want to save on the pic, you could just change the socket as DIL usually is the most expensive these days. You could also change to a MORE CAPABLE pic instead as they are cheaper (like the 16f886 if you are not tight on space).
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I don't know, but I don't see those as negative comments. I don't say anything bad about his project, I merely suggested that he could skip that max232.

Now, in reply to this, he says:


AngusMcDoon said:
So RS232 levels is allowed in the spec. The differential part is only a recommendation. How can I drive RS422 for less than 60p that the MAX232+caps cost?
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I simply answer to this:


Ridax said:
You can drive rs422 directly from the pic. Most devices would work just fine with a ground and then you use one of the I/O-pins for data. If you want to inverse the current (instead of zero it), you need two I/O-pins, one data and one data-. There should be no problem with free pins (even with the f88).
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And he responds:


AngusMcDoon said:
Driving from a PIC pin and ground is not NMEA though, as NMEA spec says EIA-232 or EIA-422. That's half and half. A PIC pin can be used for EIA-422 +, but as you say, I then need EIA-422 -, a voltage I don't have on my board, so extra components. Also this 2-pin data out wouldn't work with the HW UART of the PIC, so I'd need 2 SW UARTS.
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I write

Ridax said:
On the contrary. Driving it directly from a PIC is very NMEA/RS422. For RS422 the voltage is not very important, but they specify 5V. The PIC is easily driven from 5V, so you can use this to power the PIC and the PIC will also output this on the I/O-pins. If you want to conform to the RS422 you should use two I/O-pins on the PIC that complement (XOR) each other. This is much more NMEA than a max232.
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