Hardware Watchdog - Need Information
October 14, 2019
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In the hope of making my home automation system more reliable, I ordered some hardware watchdogs from Chinese vendors on eBay and AliExpress. A couple of parcels arrived about four weeks later. The first package should have contained two USB Watchdog Computer Automatic Restart Blue Screen Mining Game Server BTC-Miner as shown below.

These can be found everywhere on the Web. Apparently, cryptocurrency miners are plagued with errant "mining rigs" that need to be restarted to avoid losing too much money. The eBay vendor had a working link to software which was a rarity. Surprisingly there was a user manual in the archive. Also surprising was its opening paragraph and accompanying picture.

Are the two hardware watchdogs functionally the same? I may never know as this is what was in the package received.

Will the vendor make good on his promise to send the correct items? Stay tuned to this channel to find out.

There were a couple of "Hardware WatchDog PC USB Crash Automatic Recover For Mining Unattended Operation air compressor valve" that are of a different design in the other package. With such a description one would think they are capable of handling an air compressor valve!

As usual with such items, there were no instructions included with the devices but the following was on the vendor's Web page.

Clearly the wiring instructions do not match the photograph on the right which is accurate. It does appear that the correct connections are as follows:

RST1Reset connectorno polarity
RST2Reset connector
HD-Hard drive indicator lightpolarity ambiguous
flip connector if not working
HD+Hard drive indicator light

For those that want to use this with a desktop computer, it will be necessary to make up some connectors to connect the case reset button and hard drive LED to the motherboard in parallel along with the hardware watchdog. More expensive models seem better designed in this respect, but that is not important for my purpose.

As no software is used with this device, the function of the USB connector is to provide power only. As far as I can tell the watchdog is meant to be fed by hard drive activity. If no activity is detected for a period of about 2.5 seconds, then the reset relay is closed (the RST1 and RST2 pins are shorted) for a period of 9 seconds then opened for 9 seconds. This is repeated 8 times and then the relay is open for 2.5 minutes. The whole thing repeats if the watchdog is not fed. The graph is more eloquent.

On power up, the relay remains open for 2.5 minutes. My intention is to use these on single board computers especially the Orange Pi Zero which has a hard time recovering from power failures or glitches. Hopefully it boots in that amount of time so that it becomes possible to feed the watchdog before it would initiate another restart. Unfortunately there is no obvious way to change the watchdog time delays. Perhaps these are set by resistors or an R-C circuit but I can't make out the markings on the two integrated circuits to get some information. Does anyone have any experience with this? If so please drop me a line using the mail link at the bottom of the page.

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