Bad idea?

[Balderbraa]

The picture should explain.
Would it be a bad idea to add the red wire to jumpstart the relay?
Must admit i allready done it, but havent had time to check if something is broken yet.

 

[premelec]

Very Bad!

However there's an easy fix - put a diode between the PICAXE and relay and also a resistor in series with the red wire.... the diode blocks back feed high voltage into the pICAXE pin...

 

[cmast]

If your already horsing 12 volts into the relay board would the extra 5v from the PICAXE do any good I wonder?

And I would put that diode to the left of the red wire 'jump lead' connection too!

 

[hippy]

Extremely bad

You are applying 12V to an output so could permanently damage the PICAXE. If that output is active low the 12V could easily burn out the pin, the 12V could also leak through the internal clamp diode to the +5V rail and damage the entire PICAXE and whatever is supplying the 5V.

As you've done it, if you have problems downloading into the PICAXE, the program not behaving as it should, then that is probably why. Even if there's no apparent damage you don't know what damage has been done internally which may come back to haunt you later. If something in the chip does fail one day no one can predict what chain of damage that may cause.

 

[graynomad]

Am I missing something here? Apart from blowing up the Picaxe, what exactly is the red wire supposed to do anyway?

 

[hippy]

It seems to me an attempt to force the relay to operate even when not turned on by the PICAXE for testing or other purposes. The principle is sound, say to check the relay does operate and isolate an issue to the PICAXE or its output driver - just that the mechanism is not sound nor safe to use.

Re-reading the first post, it's not clear if "PICAXE-18X" is an actual PICAXE chip or a PICAXE board fitted with a PICAXE-18X and Darlington Outputs. If the later the Darlingon can only sink current and not source it.

 

[Dippy]

VERY VERY VERY VERY BAD IDEA.

Stuffing 12V into a PICAXE output will almost certainly result in you having to order another one.

A PIC 'Output' is NOT like some open relay contacts.
It means (usually) a push-pull 'Output stage' - a bit like many op-amps etc.
But limited electrically - see Data Sheet.


Moving On...
What is this "Relay Board"?
Does it contain any active components?
Give us a schematic.

If you want manual override for most things then it can be done.
But you need to provide the FULL DETAILs, before we can tell you where/how to connect things.

 

[graynomad]

It seems to me an attempt to force the relay to operate even when not turned on by the PICAXE for testing or other purposes.

I see, if that's the case this is something you do once or twice to verify that things work then never do it again. So it's not worth having extra components, just disconnect the Picaxe to do the test, then put it back.

OTOH this may be a manual override to be used by the final application.

But then if it's a straight Picaxe (and presumably a 12v coil) the normal operation won't work anyway. So it must be a board with OC or OD outputs or maybe there's some logic on the relay board, or maybe...

I guess we're just guessing.

 

[Dippy]

"I guess we're just guessing"
- yup, that's why I asked the questions ...

 

[Balderbraa]

The relay board is transistor driven much like the interface circuit in the manual. I cant find any schematic or datasheet but it runs on 12v and accept signal input from 3-12v @5ma.I have no problems downloading new programs to the chip and every thing runs ok for the moment.

My initial problem was that the PicAxe would not turn on the relay when it was supposed to so i tried jumpstarting the relay (wich worked). Later on i found a lose (or loose) wire connection and fixed it and now everything works fine.

The reason why i asked was to determin the likelyhood of instant magic smoke escaping or more subtle errors coming later.

Now i feel pretty sure that the PicAxe actually was disconnected the time i did not think at all.

Thanks for your time and excuse my french.