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The Ocelot is a hardware home automation controller which provides an easy means to transmit and receive infra-red, X10, input and output switching etc for standalone and mission critical applications. Homeseer provides a free plug-in for this device allowing control of its infra-red or input/output functions via a serial port. The system allows for several modules including a 16 output infra-red controller called the SECU16-IR. This allows you to place IR diodes on each of your equipment and address them individually for control. One of the disappointing aspects of the Ocelot and SECU16-IR is that the output drive is very low and is only capable of driving low power Infra-red LED's over a short distance. Like many other people, I wanted to be able to install a high powered IR device within a room and not stick individual sensors on each item of equipment to be controlled. Guy Lavoie came to the rescue for the Ocelot with his article at Hometoys.com. This works very well and many people have copied this circuit with excellent results. One of the problems with this circuit is that it needs a separate power supply and it does not work very well on a SECU16-IR. I found using Guy's circuit, the IR LED would always be on causing attenuation to other IR controlled devices within the same room. Further investigation of the SECU16-IR revealed that the output jacks were in fact connected in series with the output transistor collector and the unregulated supply via a 1K resistor. This meant that the transistor in Guys circuit was always biased on causing the problem. To solve both these problems, I decided the best method was to use a Opto isolator. These are very cheap and come in single, dual and quad packages. This totally isolates the Ocelot SECUIR-16 from any harm and allows the use of the same DC supply if necessary. Another feature is that all LED's are common ground and not common positive.  Virtually any Opto Isolator can be used. Please note that the output transistor has to be a PNP device. The BC641/2N5322 is capable of a collector current of 2A so it is possible to drive the IR emitters very hard without damage. This circuit is suitable for both the Ocelot and the SECU16-IR. Using the specified transistor, this will drive two independent LED outputs directly. Just add a second 15R resistor and IR LED from the BC461 collector and ground. If you require more IR illumination within the same room, then you can add additional IR LED's in series with the first. A maximum of 5 can be used on a 12V supply.  |
