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 Forum index » DIY Hardware and Software » Arduino
short protection for cv-out
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selbersuess



Joined: Mar 21, 2017
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Location: Trier

PostPosted: Thu Apr 13, 2017 4:26 am    Post subject: short protection for cv-out Reply with quote  Mark this post and the followings unread

hello friends,

i have a question (maybe a stupid, i'm not very experienced with electronics, more in programming.) about what happend when cv-out shorten to ground.

for example:

i built a midi2cv by an arduino with 8 cv, 4 gate and 4 trigger outs.
to fit in a small unit, i used stereo jacks.

the signal line goes:

midi-in -> arduino -> mcp4922 -> lm324 -> 1k resistor -> cv-out-jack

my question is, what happend if i plug in mono-cable. is it a problem?
if yes, is there a simple way for a short protection?

thank you
daniel
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Grumble



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PostPosted: Thu Apr 13, 2017 10:14 am    Post subject: Reply with quote  Mark this post and the followings unread

The 1k resistor is sufficient to prevent the 324 from breakdown due to short circuit.
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PHOBoS



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PostPosted: Thu Apr 13, 2017 11:40 am    Post subject: Reply with quote  Mark this post and the followings unread

LM324 is also short-circuit proof by itself. Since you are using it to generate
a CV signal it might even be better to leave the 1K out altogether. This will
prevent any attenuation when you connect it to something.

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gdavis



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PostPosted: Thu Apr 13, 2017 11:47 am    Post subject: Reply with quote  Mark this post and the followings unread

LM324 is protected from short to ground on one output at a time. A short to a higher voltage than the output or on more than one output at a time could damage the part.

A brief short as the patch cable is being inserted is one thing, but I would avoid a continuous short. I don't recommend plugging a mono plug into a stereo output jack.

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PHOBoS



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PostPosted: Thu Apr 13, 2017 12:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

Embarassed oops I forgot to read the notes. shorting all outputs could indeed result into damage due to overheating.
I don't think shorting a single output would cause any problems but a resistor would of course also limit the
current in general.

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gdavis



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PostPosted: Thu Apr 13, 2017 12:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ya, in theory you should be able to short one of the outputs to ground indefinitely without any problems, I just think it's a bad practice to be relying on that by design. Especially since in use you would have to pay attention to which jacks are on the same opamp and mentally make sure not to connect more than one of them incorrectly. Someday something bad will happen.

The output resistor may be an option but as you alluded to earlier, for pitch CV it may have an audible effect on the pitch.

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Grumble



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PostPosted: Thu Apr 13, 2017 1:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

gdavis wrote:
for pitch CV it may have an audible effect on the pitch.

It all depends on the impedances of the connected input(s).
If all the inputs connected to this CV are buffered, it is not a problem, but if the connected input is a potentiometer of say 100k, the mismatch will be 1% of the full scale, and it gets worse if more than one input is connected to this CV.
So that indeed is something to take into account.
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selbersuess



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PostPosted: Thu Apr 13, 2017 1:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

until now i used stereo plugs and was observant to that, i will do furthermore.
the motivation was to have more space in my modular.
now i realize that it was not a perfect idea.
thank you
daniel
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Grumble



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PostPosted: Fri Apr 14, 2017 11:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

I just can't understand how a mono jack would be different from a stereo jack in terms of shorting the output? Rolling Eyes
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PHOBoS



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PostPosted: Sat Apr 15, 2017 11:14 am    Post subject: Reply with quote  Mark this post and the followings unread

If you plug a mono plug into a stereo socket it'll short one connection (ring) to GND.
Guitar effects sometimes make use of this to power the device on/off.

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Grumble



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PostPosted: Sat Apr 15, 2017 3:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

selbersuess wrote:
until now i used stereo plugs and was observant to that, i will do furthermore.
the motivation was to have more space in my modular.
now i realize that it was not a perfect idea.
thank you
daniel

If the only reason to refrain from using mono connectors is worries about shorting outputs, I would use mono connectors still the same.
Because for mono and for stereo connectors both the tip of the connector will touch the gnd connection when inserting the plug into the connector.
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gdavis



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PostPosted: Sat Apr 15, 2017 4:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

Grumble wrote:
selbersuess wrote:
until now i used stereo plugs and was observant to that, i will do furthermore.
the motivation was to have more space in my modular.
now i realize that it was not a perfect idea.
thank you
daniel

If the only reason to refrain from using mono connectors is worries about shorting outputs, I would use mono connectors still the same.
Because for mono and for stereo connectors both the tip of the connector will touch the gnd connection when inserting the plug into the connector.


Yes, inserting can create a momentary short, which is why modular outputs typically have some sort of short protection. But a stereo jack creates a continuous short, and as we've discussed here already, a momentary short on a single jack when plugging in is a different scenario than continuous shorts on potentially multiple jacks.

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Grumble



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PostPosted: Sun Apr 16, 2017 12:34 am    Post subject: Reply with quote  Mark this post and the followings unread

Ow.... I misread the whole thread Embarassed
I failed to notice that the stereo jacks were used as...wel...stereo jacks Rolling Eyes
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