Here's the challenge: I have available an ASUS RT-N16 router running Tomato USB firmware attached to a fixed wireless receiver, and I'd like to have a watchdog timer that resets both when there is a loss of Internet connectivity.
I have access to the semiconductors available at the Canadian version of Radio Shack: http://www.thesource.ca/estore/category.aspx?language=en-CA&catalog=Online&category=Semi+Conductors%2fIC%27s which is sadly limited to a 555 timer, an NPN transistor, PNP transistor, and a 5 V regulator. All at nicely inflated prices. (i.e. the 555 costs $5 instead of $0.20.) One solution is to tap off an LED on the RT-N16, which I believe can be software controlled. (Preferably using a phototransistor mounted to the exterior of the router, but it doesn't look like I can get my hands on one of those.) The router has USB ports, so a USB-to-parallel or serial adapter is another possibility, if I can get my hands on one at a reasonable price (looks like the same vendor has them for $35 and $50 respectively), and I can figure out how to toggle outputs on it via a script. A script running on the router can perform any desired connectivity checks, then pulse the LED (or I/O line), and loop. This way a crashed router or loss of connectivity will trip the watchdog. The external 555 circuit then would be setup as a resettable timer, similar to this watchdog circuit: http://www.delabs-circuits.com/cirdir/digital/555/del00013.html I'd like to have it drive a solid state relay, but it looks like this mechanical relay: http://www.thesource.ca/estore/category.aspx?language=en-CA&catalog=Online&category=Relays is all that is available. I'd use the normally closed contacts to power the devices being reset, so if the watchdog fails, it'll be less likely to perpetually disrupt power. Might need another 555 to control the power reset duration (which might need to be 30 seconds or so) and/or a 2nd relay to power cycle the fixed wireless receiver before the router. Any thoughts on how to simplify any of this? Theoretically, the router hardware includes a watchdog timer, and if it can be proven to be reliable, and controlled by my software instead of Tomato (if it even uses it), then most of this could be turned into software, and I'd just attach a transistor driver to the LED output to control a relay (and maybe a 555 delay to a 2nd relay). But there are several "ifs" there that I may not have time to resolve. Some searching turns up that Tripp Lite has some UPS models with built-in watchdog timers and USB connectivity. Here's the page where they describe the software used to support that: http://www.tripplite.com/en/products/model.cfm?txtModelID=2590 That might be the ideal option, if I can source one here, and can reverse engineer the software (or, if already supported on Linux, port it to the router). -Tom _______________________________________________ Hardwarehacking mailing list [email protected] http://lists.blu.org/mailman/listinfo/hardwarehacking
