hi all I was wondering if you could give advice for some ideas for a "watch dog circuit" (not watchdog timer) hardware wise the purpose of this is that it will stop all outputs of a circuit if the micro controller turns off, if you could provide any hints and or tips of topologies I should look at that would be appreciated
Kind Regards
J

 

can you share a schematic?
Are all these outputs coming from the micro anyways.. So wouldn't it "stop outputting" when its off anyways?

 

can you share a schematic?
Are all these outputs coming from the micro anyways.. So wouldn't it "stop outputting" when its off anyways?

hi sorry so basically this circuit will be controlling Contactors which will be connector to this circuit, what I would like to do is add protection so that if the microcontroller suddenly turns of the contactors also do likewise.

 

Make the contactors active only when a micro output is high.
If micro goes off, outputs go low, contactors go in-active.

 

Make the contactors active only when a micro output is high.
If micro goes off, outputs go low, contactors go in-active.

Could this just be done with a simple AND gate, with one connection to the Micro and the other to digital High?

 

why would you need an AND gate when the micro alone can do this ?

 

why would you need an AND gate when the micro alone can do this ?

This is a fail safe in case the micro just stops functioning, perhaps I'm not phrasing it correctly this is what I'm after:
Design a simple hardware watchdog circuit that will drop out contactors/HVIL safety loop when the microprocessor stops working.

 

Micro processors has a feature called "watch dog timer" specially for this reason and more.

What makes you think an AND gate will help ?

 

Micro processors has a feature called "watch dog timer" specially for this reason and more.

What makes you think an AND gate will help ?

In retrospect the AND gate would have been pointless, from the design brief I'm working from it mentions watchdog hardware is this seperate to a watchdog timer or the same thing? I am new to electronic design, I saw the feature but assumed that this was a software feature.

 

WDT is hardware module. Can be used to reset the uC if it latches up.

 

WDT is hardware module. Can be used to reset the uC if it latches up.

ah I see do you by any chance have any datasheets for modules of this style, would really be appreciated

 

WDT is hardware module. Can be used to reset the uC if it latches up.

the micro I'm using is: Piccolo TMS320F28035

 

Then you wait a while until someone familiar with that comes along

 

Here

 

Here

I already have the datasheet for the micro there is a mention of a watchdog incorporated is this the same thing you are referring to?

 

If you can't upload the schematic then you can draw a block diagram to show what you trying to do and draw more clearly at that output parts that you want to control.

>if the micro controller turns off
What does the meaning of turns off, could you define it clearly?

 

Like some have previously mentioned, why not use a output active High to control a relay which will drop out when the micro drops out of run?
This relay would simply control/switch the coil voltage supply off on the contactors on micro fail?
Max.

 

Hi all managed to find a solution thank you all for the suggestions

 

Hi all managed to find a solution thank you all for the suggestions

So are you going to tell us what it was?
Max.

 

I was wondering if you could give advice for some ideas for a "watch dog circuit" (not watchdog timer) hardware

Normally a "watchdog timer" is used for that purpose since it indicates that the micro has stopped working normally.
Monitoring a static output does not insure that you will detect a micro that gets hung.
Why do you not want to use a timer?