Watchdog timer

[fernando_g]

Now that the Picaxe devices no longer have a dedicated reset line......what would be the best way to implement a watchdog timer and voltage supervisory circuit?

I've been thinking of a high side Mosfet toggling the Vdd line, but that doesn't seem a very elegant solution

 

[srnet]

Now that the Picaxe devices no longer have a dedicated reset line......

Not correct, 28X2 and 40X2 most definetly have a dedicated reset line.

 

[fernando_g]

I stand corrected.... Pin 1 is the reset input.
that tells you that I'm only a user of smaller Picaxes, and haven't really studied the larger Picaxes. I bought a 28X1 a while back, but have not found a complex enough project to use it.

Let me re-phrase my question:

Now that the Picaxe devices smaller than 28 pins no longer have a dedicated reset line.......what would be the best way to implement a watchdog timer and voltage supervisory circuit?

Further edit....I've read Manual 1, page 47, "Reset Circuit". Duh!

 

[srnet]

Well the easiest way to implement a watchdog is to use a PICAXE that has a reset pin.

$50SAT implemented both a timed watchdog and a voltage supervisor. Whilst the reset pin of the 40X2 was used, the circuit also had the components (two MOSFETS) that disconnected the power for a short while, which would do what you want so take a look at that circuit.

 

[fernando_g]

Yes, with a MAX6369.

Thanks!

 

[srnet]

The LT2917 is an alternative device, it is a watchdog timer and voltage supervisor.

But both the MAX6369 and LT2917 are only available in small, not easy to solder, SMT packages.

The benefit of these two devices is that the timout periods can extend into many seconds, which is required for circuits that go to sleep for long periods.

If there is an easy to solder watchdog, with a long timeout and in a soldering friendly SOIC package I would be interested to know.

 

[PhilHornby]

Software Reset?...

Let me re-phrase my question:

Now that the Picaxe devices smaller than 28 pins no longer have a dedicated reset line.......what would be the best way to implement a watchdog timer and voltage supervisory circuit?

If you take the "(In) / Serial In" Pin (e.g. C.5 on an 08M2) HIGH, you get a RESET (assuming no DISCONNECT statement in the code). Presumably this requires the 'Picaxe firmware' to be alive and kicking, so wouldn't be of any use in getting out of a 'hung' state.

I've not investigated which Picaxe statements might block this response - I just happened upon it by chance. I added a switch to my latest project, and "(In) / Serial In" was the only available pin. I was about to start writing code to implement a RESET / Restart option, when I noticed it was unnecessary

 

[MFB]

The MAX6301 is available in an 8-pin DIL package and the time-out period can be set for tens of minutes, if the external capacitor option is used.

 

[hippy]

If you take the "(In) / Serial In" Pin (e.g. C.5 on an 08M2) HIGH, you get a RESET

I've not investigated which Picaxe statements might block this response

Basically all those blocking commands which would stop a download from occurring; waiting for SERIN, IRIN, KBIN.

 

[fernando_g]

If you take the "(In) / Serial In" Pin (e.g. C.5 on an 08M2) HIGH, you get a RESET (assuming no DISCONNECT statement in the code). Presumably this requires the 'Picaxe firmware' to be alive and kicking, so wouldn't be of any use in getting out a 'hung' state.

I've not investigated which Picaxe statements might block this response - I just happened upon it by chance. I added a switch to my latest project, and "(In) / Serial In" was the only available pin. I was about to start writing code to implement a RESET / Restart option, when I noticed it was unnecessary

Wow! very valuable advice!

 

[srnet]

The MAX6301 is available in an 8-pin DIL package and the time-out period can be set for tens of minutes, if the external capacitor option is used.

Good find.

Some time back I spent several hours scanning through the Farnell list of Watchdogs, but did not come across it.