DC to Blue Light, and everything in between!

List,

We live in marvellous times, when you can pop out to B&Q and buy solar garden lamps for under a fiver, wireless doorbells and even wireless remote power switches from Lidl's for £20 for a set of 4.

For the experimentor, these cheap gadgets from China offer some real possibilities for interesting home automation and control projects. Here's a few of my recent projects.

A couple of years back, I bought a couple of solar lamps to see what made them tick, so to speak, and found a wealth of useful components.

A solar lamp is essentially a small pV panel, about 50mm square, a couple of AA sized nicads, a white LED, a light sensor to determine when its dusk and a simple controller board with a voltage booster circuit that boosts the 3V from the nicads up to about 11V so as to more efficiently drive the white LED.

No only do you get all that, but a neat waterproof case, that holds the batteries and gubbins, and actually acts as a reliable source of (very modest) illumination - even 2 years on.

This got me thinking about what else I could use the lamp for, as it is basically a solar powered nicad battery charger, with enough capacity to run a microcontroller or wireless thermometer.

I had previously been experimenting with PIC microcontrollers and short range wireless. I have a long garden with a greenhouse about 150 feet away from the house. An ideal application would be a solar powered greenhouse thermometer. However my greenhouse is full of junk, so the thermometer was used for logging the temperature of my compost heap, another 30 feet further on.

Why log the compost heap temperature? - well I had an idea, that in the summer months, the rotting grass cuttings might be used as a source of hot water, that was before I bought my Navitron panel.

The next possible application is for a wireless thermometer to be fitted at the manifold outlet of the solar panel. This could be some distance away from the laptop, and could be integrated into the home monitoring system.

Not only does it measure temperature, but the power output of the solar cell is proportional to the incident sunlight, and it could be also used to give a measurement of the strength of the insolation. This signal could be used to control the pump speed of the circulation pump, slowing it down during periods of overcast or cloud.

Small, waterproof and self-contained, it could easily be mounted on top of the manifold, and at night, subtly illuminate your Navitron panel - for all your neighbours to see.

The 50mm square panel provides a surprising amount of current for it's size. In hazy sunshine it will produce about 25mA at a maximum of 4.2V, which is more than plenty to run a small microcontroller, with the AA nicads providing sufficient backup for running during darkness hours.

Short range wireless devices are getting much cheaper, with Wilkinsons selling 433MHz wireless doorbells for under a tenner. The transmitters and receivers of these can be modified to activate remote relays, or in one case, used to decode the wireless protocol from my Drayton wireless boiler thermostat control.

A recent design I did, put a receiver and transmitter on a pcb for a component cost of around £3. Drawing only a few milliamps at 3V, there is no reason why smart "wireless nodes" could not be built into a whole host of devices. If you need to have a source of low voltage power for switching relays, then build the node into the case of a plug in dc supply -giving you say a 12V 1A dc supply that can be turned on and off remotely.

Who needs power guzzling Bluetooth or Zigbee, when all you want to do is convey a temperature or other analogue reading, or turn a relay on and off?

Another field that wireless node technology could be used is for the smart zoning controls for central heating.

A wireless thermostat is installed into every heated room and conveys temperature data back to a central receiver. The receiver makes a decision, based on room temperature and time of day, whether that room needs heating or not, and shuts down the individual radiator.

One very easy way of doing this, if you fit a standard thermostatic radiator valve and gently warm the metal "bulb", it will shut off the radiator within about 10 to 15 minutes. This can be done with a power resistor, dissipating about 1W of power. Each radiator is fitted with a heated sleeve, that fits over the control valve. A plugtop dc power supply, provides the small amount of power to warm the resistor. This dc supply can be controlled by whatever home automation package you see fit with either a wireless or X10 type control. As thermostatic valves are so cheap, get the sort that can be fitted to either flow or return (non-directional) and fit one at either end of the radiator. One remains under manual control whilst the other, in series offers remote control.

BTW If anyone uses Drayton Digistat central heating controls - I have the protocol and code to generate "boiler on" and "boiler off" commands, from a 433MHz transmitter plugged ito a PC or other source of RS232.

Ken