This code implements a standalone watchdog timer, allowing the target device to be restarted (or other action taken), when no input is received after a set amount of time (defined in AWT_TIMEOUT).
This was originally implemented with the objective of restarting an Android phone that was repurposed as an IP camera. Given that the device could occasionally shutdown due to lack of battery power, or crash due to software bugs, and because it would be important to maximize its availability without human intervention, with that in mind the idea of creating this device came to fruition.
If you have curiosity, the IP camera project was described in this blog post:
http://creationfactory.blogspot.pt/2016/03/repurposing-old-android-phone.html
The original idea was to have this Watchdog Timer (WDT) device close the circuit from the power button of the Android device, when there is no incoming pulse for a set amount of time.
On the other hand the Android device would be responsible for sending a pulse (e.g. through a cron expression) after a set amount of time. This pulse is received via the GP2 pin. For example if the AWT_TIMEOUT parameter would be set to 120 seconds, we would set the Android device to send pulses within that period, e.g. every 30 seconds.
If for any reason the target device (Android phone) is completely irresponsive, the assumption is that it will not be able to respond with the pulse. Once the WDT timer expires, the microcontroller will set the GP1 pin high for enough time to cause the target device to restart (this may depend on the phone or other device this circuit is to be used with). This time is defined by the RESET_PRESS_DURATION constant.
This project can be built on the MPLAB X IDE. It requires the XC8 toolchain for compiling the firmware image.
For building it can simply be opened in the IDE, and launch the project build. Alternatively you can the programming of the device directly, if you have a PIC ready to be flashed in your programmer. It should be possible to use practically any Microchip programmer to flash the device (e.g. a PICkit 2 or 3).
You probably can have success with one of the Arduino based programmers that are around, but I haven't personally tested.
Below are the pin mappings for this firmware:
+---------------+
+5V - --|(VDD)| |(VSS)|-- - GND
| \---/ |
N/A - --|(GP5) (AN0)|-- - N/A
| |
N/A - --|(GP4) (GP1)|-- > PWR_BTN
| |
N/A - --|(GP3) (GP2)|-- < WDT_RESET
+---------------+
The example below is applicable for a target device which can be restarted via the momentary press of a button. It is assumed that this is an active low input, as when the microcontroller GP1 pin is set high, the transistor will cause the button input to be pulled down:
- Define a separate timer, in order to wait longer for devices that take a long time to boot (above AWT_TIMEOUT);
Author: Luis Teixeira (https://creationfactory.co)
Licence and copyright notice:
Copyright 2020 Luis Teixeira
Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, softwar distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.