The objective is to have a means to monitor activity on a master processor, for instance, an ESP8266 (or ESP32 or any other type of processor). The master processor needs to have a ‘hartbeat<\/em>‘ signal that can be fed to the EHWDT. This can be done by toggling a GPIO pin on- and off. For visible feedback you can add a LED to this GPIO pin so you can monitor the hartbeat.<\/p>\n\n\n\n The master processor needs to send at least every\u00a0 In the image above you see a typical reset circuit for an ESP processor. [ESP-RESET] comes from the ATtiny85 (PB3, DIL-2). The Q3 MOSFET works as a level-shifter (if needed) and on a HIGH signal it will pull [RESET] down.<\/p>\n\n\n\n PB4 (DIL-3) on the ATtiny85 is used to control (in this case) a relay but if you don’t need a relay you can remove this part of the circuit (Q2, R5 and R6). PB0 (DIL-5) outputs a signal to the [WDT-LED] (D2) which will, after every received “Keep Alive” pulse go “HIGH” for 500 milliseconds). <\/p>\n\n\n\n Two seconds before the circuit will reset the master processor the PWM_LED will blink rapidly.<\/p>\n\n\n\n You can find the source for the ATtiny85 WDT on github<\/a> as an Arduino Sketch.<\/p>\n\n\n\n During the ‘power on<\/em>‘ fase there is some visible feedback during witch time the master processor needs to settle. First the SGNL_LED and the REL_LED blink a few times. Then the REL_LED dims and the SGNL_LED blinks for 25 seconds. After that the EWDT waits for three hartbeat pulses from the master processor. Now ‘normal operation<\/em>‘ is started and the EWDT is ‘armed<\/em>‘.<\/p>\n\n\n\n If the SGNL_LED starts blinking fast it means that the master processor did not send a hartbeat for more than two seconds and both the master processor and the ATtiny85 will reboot.<\/p>\n","protected":false},"excerpt":{"rendered":" This post has 5,439 keer bekeken \/ views Sometimes the internal Watchdog Timer (WDT) of a MCU is working more against you than that it ‘helps’ you. Also an internal WDT is not always up to the task of resetting … Continue reading ![\"\"](\"https:\/\/willem.aandewiel.nl\/wp-content\/uploads\/2022\/03\/ATtiny85EWDT-1.png\")
<\/a><\/figure><\/div>\n\n\n\n_MAX_HALF_SECONDS<\/code>\u00a0seconds a “Keep Alive<\/em>” pulse to the WatchDog [WDT-FEED] (a 3v3 signal is level-shifted by Q1 to [WDT] (PB2, DIL-7)). If the WatchDog does not receive this pulse in time it will make [ESP-RESET] (PB3, DIL-2) HIGH for 500 msec to reset the master processor. <\/p>\n\n\n\n<\/a><\/figure><\/div>\n\n\n\n<\/a><\/figure><\/div>\n\n\n\nBoot sequence:\n==============\n State | REL_LED | SGNL_LED | Remark\n ------------+---------+---------------+-------------------------\n Power On | Blink | Blink | Inverse from eachother\n | | | Relays \"Off\"\n | | | Next: \"Fase 1\"\n ------------+---------+---------------+-------------------------\n Fase 1 | Off | 900 MS On | repeat for 25 seconds\n | | 100 MS Off | Relays \"Off\"\n | | | Next: \"Fase 2\"\n ------------+---------+---------------+-------------------------\n Fase 2 | Off | 500 MS On | wait for 3 Feeds to pass\n | | for every | Relays \"Off\" \n | | Feed received | Next: \"Fase 3\"\n ------------+---------+---------------+-------------------------\n Fase 3 | Off | Blink Fast! | wait for 3 Feeds to pass\n | | for 2 seconds | Relays \"Off\" \n | | | Next: \"Normal Operation\"\n ------------+---------+---------------+-------------------------\n Normal | On | 500 MS On | Relays \"On\" \n Operation | | for every | \n | | feed received | \n | +---------------+-------------------------\n | | Blink fast | If no feed within 2 \n | | | seconds: \n | | | Next: \"Alarm State\" \n | | | else: \"Normal Operation\"\n | | | Relays \"On\"\n ------------+---------+---------------+-------------------------\n Alarm State | Off | Off | Relays \"Off\"\n | | | Reset ESP8266\n | | | Restart ATtinyWatchDog \n | | | Next: \"Power On\" state\n ------------+---------+---------------+------------------------- <\/pre>\n\n\n\n