As described last month, basic applications requiring simple on/off control can be driven directly from the PNS with only a few extra parts. However, more complex applications often call for a dedicated controller, perhaps based on a PICAXE chip.

Fortunately, a PICAXE chip in such a system can be programmed to interact with the PNS by sharing information (such as sensor data) in a common area of memory. These variables can then be displayed within web pages or even manipulated by the PNS to alter system behaviour.

Temperature controller

Environmental temperature control is one example of a process that demands a dedicated control system. A temperature controller might be used to regulate the temperature in a dwelling, greenhouse, fish tank or even home-brew storage tank – to name a few examples!

An outline of a rudimentary controller that could be used to maintain room temperature (in a cold-weather climate) within a specific range is shown in Fig.1. It is based around a PICAXE-28X chip, which controls a heater and fan via transistor switches and relays. A DS18B20 sensor provides temperature feedback.

If the PNS were not connected to the temperature controller, then the BASIC program in Listing 1 would be all that’s required. The program waits until the temperature drops below a minimum of 16°C, at which point the heater (on output 2) is switched on. When the temperature subsequently rises above 22°C, the fan (on output 5) is switched on.