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Forum Index : Microcontroller and PC projects : Expert opinions please...
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| Malibu Senior Member  Joined: 07/07/2018 Location: AustraliaPosts: 228 |
Still having occasional freezes on the WebMite - much more stable now than previous, but still something I want to try and avoid if possible. (99.99% sure now that it's SDK based, not MMbasic) I've been toying with a 'last resort' hardware based Watchdog and came up with this idea  A simple concept: Monitor the heartbeat LED on TP5 and feed the signal to a watchdog timer to reset the Pico after 60 seconds if the heartbeat stops. A few concerns though 1) using TP5 is not recommended in the Pico datasheet because it will only go high to the LED forward voltage (measured at 1.9V), hence the schmitt driver to level shift to 3.3V and 2) the possibility that I might get stuck in a continual loop of reset during program load (doubtful, but still a maybe) and 3) Does the RUN pin on the Pico still work during a system freeze-up? Any thoughts or ideas by those more knowledgeable than me in hardware design? (That'd be pretty much everyone!)  John |
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Mixtel90 Guru  Joined: 05/10/2019 Location: United KingdomPosts: 6760 |
I must confess that simply because I haven't got either of those chips my first attempt would be a transistor fed from Heartbeat being used to short out the timing capacitor on a 555, with the output from that feeding back as the reset signal. I'm a bit old fashioned, I'm afraid. lol The fun is, of course, in getting the Pico to start in the first place as the 555 will have timed out. . Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2129 |
Another 555 to to disable the first one until the heartbeat first starts blinking after power-up? |
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| Malibu Senior Member Joined: 07/07/2018 Location: AustraliaPosts: 228 |
I hear ya, Mick  555 was my first go-to as well, but it all started to snowball and finished up with a 556 design to overcome the solution Phil pointed out (even then, still with a few issues) The TLP5010 seems like an interesting device with time intervals between 1s and 2hr, just by changing the resistor value - 60s seemed like a good number John |
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| phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2129 |
Another standard PicoMite may be cheap enough to use as a heartbeat monitor and reset trigger. Any issues can be sorted out in its software. I think the Pico DIN thresholds will be ok without a level shifter. If not use AIN. In the unlikely event that pulling the RUN pin low doesn't work when locked up put a transistor in series with the WebMite power supply and switch that from the monitor Pico. Edit Me Thick, just switch 3V3_EN. It has 4.7V on it so a transistor may still be needed to pull it low. Edit 2 No you don't need a transistor, just a 10kΩ resistor between the output pin and 3V3_EN works. > pin(gp6)=1 In this test the Pico restarts itself.> setpin gp6, dout > pin(gp6)=0 PicoMite MMBasic RP2040 Edition V6.00.00RC15 Copyright 2011-2024 Geoff Graham Copyright 2016-2024 Peter Mather > Edited 2024-11-17 09:57 by phil99 |
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