Do not use a cannon to kill a mosquito

Some time ago I installed a series of IP cameras to keep an eye on the horses at the farm. With the dodgy power, the sometimes less than stellar performance of the IP link to the farm (it is a long radio link) and the generally poor firmware found on domestic IP cameras, it is not a rare event that that the cameras lock up and need a power cycle.

My original plan for fixing the issue was to install an Arduino with an Ethernet driving a relay and have a Nagios event handler tell the Arduino to bounce the relay. I already use something like this to help fix the WiMAX radio link when it gets confused. Reducing the number of calls I make to my saintly mother-in-law and brother-in-law to help bring the link back up.

After a face-palm moment I realised I was over engineering this problem and already had a piece of equipment that gave 90% of the solution - a ToughSwitch POE. This PoE switch has a watchdog facility that reboots devices if they fail to ping for a sufficiently long period of time - I deployed this device to control my outdoor APs in November of 2013 to great success. All that was needed was to make the cameras PoE devices ...
Ubiquiti supports two types of PoE - 24V power injector and 48V phantom - the switch I have provides only the 24V variant other models provide both. You can purchase adaptors that will provide various voltages from the 48V version easily. Unfortunately the power injector solution is a bit more DIY.

Essentially for the 24V solution you need to pass pins 1,2,3 and 6 from the switch to the device for Ethernet connectivity (max speed of 100Mbps) and then pick up the 24V supply from pins 4,5 (positive) 7,8 (negative) and reduce the voltage to that required by the device in my case 5V for one camera and 12V for the other.

I chose to use Traco Power DC/DC Converters TSR-1 Series ( supplied by Element14. These nifty little DC/DC converters are 95% efficient, run fairly cool and are tiny - they have the same pinouts as the venerable 78xx series linear regulators.

A small piece of strip board is used to mount the DC/DC convertor.

Applying some heat shrink around the strip board protects against short circuits.

Easily constructed, avoided unnecessary coding (the toughswitch handles it all provided the device can be pinged) and simplified a problem (no need for Nagios to handle an event) ... Truly not killing the mosquito with a cannon1

1. “Do not use a cannon to kill a mosquito” - Attributed to Confucius.