Troubleshooting Communications

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gtslabs

Member
I made a project a few years back using a 28X1 chip to read 8 DS18B20 temperature sensors and send to my com1 port.
Well it crapped out. I have voltage at all my sensors (inputs) and I know my program is running because I have an LED flash after each readings are taken every second.
But I am not getting any data in my serial port.
I used the most basic wiring requirement from the chip data sheet for Tx / Rx.

How can I trouble shoot the serial output using a multimeter?
I thought I should see a ~5v spike every second but I dont have any voltage across ground and output pin 7.
Any Ideas?
It has been years so I can not easily troubleshoot in field.
 
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G

gtslabs

Member
I will once I find my old schematic.
But should I be able to read the voltage spike on the output using a Digitial voltage meter?
 
S

srnet

Senior Member
gtslabs said:
Well it crapped out.
Click to expand...
So we can all understand, can you clarify what you mean by 'crapped out', is it no longer working ?

A multimeter wont tell you much about a serial interface, it may not even notice.

A logic probe or a scope is most useful in these circumstances.
 
G

gtslabs

Member
I checked all my voltages and grounds and they appear to be as designed.
I hooked it up to another computer using a different serial cable and I am getting no output.

I am using a 28X1 Chip.
How can I get the programmed code from the chip BACK into the picaxe editor?

I found my logic pen and my pin7 Tx out is pulled low.
 
G

Goeytex

Senior Member
"How can I get the programmed code from the chip BACK into the picaxe editor?"

Unfortunately that cannot be done as the Picaxe is read protected. If you do not have a copy of the original
code you will have to start over.
 
J

John West

Senior Member
Always, always, always keep copies of your code for any project you build, especially one that you keep in service for an extended period of time. Keep hard-copy copies, keep multiple software copies in various locations.

I write very little code (I'm still a Noobie at PICAXE code) but I try to keep enough copies of code I do write that I don't even have to look for it, it's in my way.

I'd even suggest you email a copy of your code to yourself (if you have an account similar to Yahoo accounts) so it resides elsewhere in a place you can always find it.

Code is gold.

BTW, lacking a logic probe or scope on occasion, I've checked for data transmissions with an LED and a resistor, with a small capacitor across the LED. It has a possibility of screwing up the data comms, but it might a least let you know if the line is toggling. A digital multimeter may completely miss a data burst. Even an old analog multimeter is a better meter for the purpose. (I've used them as well to try reading data lines. Digital scopes are really the way to go. :))
 
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P

Paix

Senior Member
A couple of thoughts come to mind.
1. Had you followed the advice that is given so often to post both code, pictures and circuit diagram of your project, then it is apparent that you would only have to download your code to be able to place it on another PICAXE chip.
2. The circuit diagram would allow a better insight into the area of circuit under question and perhaps reveal any significant areas of weakness that may have contributed to the symptoms that you are having.
3. As you are unable to reload the project code, then it's not possible to put the chip onto another board to test it independently of the circuit. Obvious I know.
4. The project is four years old - did you use lead-free solder, is the PICAXE chip socketed (and what quality socket) and could the operational envirionment a contributory factor. I am thinking here that if the circuit had been built with some very close solder joints, and lead free solder had been used that you may just have a tin whisker that has grown and now providing a short circuit in the serial comms area of your board. Unlikely, but I do remember all those fuseable ROM chips that selectively healed themselves a few decades ago and caused projects to go awry over time. Factors such as temperature cycling and damp may have caused a socket pin/chip contact to oxidise giving you a high resistance contact in your circuit.
5. Had there been any changes in the environment, floods, splashes, lightning strokes, building work, chewed or tugged by animals etc. that might even remotely have caused any event that might have disturbed the circuit or it's extended wiring?

A good clear photograph or two of the top and bottom of your circuit board would be appreciated and might help.

Rule out nothing, as the circuit was working and now isn't - so what may have happened to cause it, More likely in my mind than it just dying of it's own accord. Flexible solid wiring that has cracked internally?
 
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D

Dippy

Moderator
Yes, LED+R can help, but if you've found a Logic measurer then that's good.
Some multimeters may give a flicker to indicate something, but, other than that, the info is useless.

If you haven't backed up then wave goodbye to the code.

Have you measure at the chip pin/leg or after some other components?
Is the chip soldered or in a socket?
If in a socket, are the contacts OK , or is the chip falling out, are the legs OK?
Pull the PICAXE out and stick it back in again, maybe contacts are dirty?
Have you checked continuities?

Plus, as suggested by Paix above.
 
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