Friday, 22 March 2013

Raspberry Pi and DS18B20

This is just a test of the Raspberry Pi hooked up to a DS18B20 temperature sensor.  Using LadyAda's tutorial, this was up-and-running in about 5 minutes and sending out highly accurate temperature data over the network.  As it is much more expandable and easy to use than the LM75, I think this will have to be the weapon of choice for the heating control system.  My only concern is whether the Raspberry Pi can really be used for a 'mission critical' application, bearing in mind that today the there has been an ice storm raging across the UK which has been particularly bad here in Northern Ireland.  This would not be a day to have the heating control fail due to an OS crash!

Friday, 15 March 2013

Improved Thermometer

An improvement on the thermometer, this is a lot more practical.

I connected up my big 7-segment LED module, added the Arduino library and one extra procedure and very quickly had this thermometer with a big bright display and accurate to 2 decimal places.  I took the picture with the flash which is why the display doesn't look so bright, but trust me, it is.

The pint milk carton is to give an idea of size.  Looks like we need milk too.

A better photo without the flash showing the LED display in all its glory.

Thursday, 14 March 2013

Massively over-engineered thermometer

Went a bit daft tonight and tried out the Arduino TV Out library along with the 1-Wire library to make a slightly mental video screen thermometer.  The temperature here is 17.68 expressed as 1768 hundredths of a degree.  The DS18B20 has a very impressive 12-bit resolution so it is accurate to 0.625 degrees Celsius allegedly.

It works well enough for a bit of fun, but the TV Out library relies on accurate interrupts to get the video signal timing right and while it is fine on its own, the complex polling of the 1-wire bus must be disabling the interrupts because the screen flickers badly each time a temperature update is performed.

The flickering screen reminds me of the ZX80 or the ZX81 in 'fast' (i.e. rubbish-looking) mode, which isn't surprising because the Arduino is in a similar class to the Z80, except twice as fast and with a lot more memory than either of the original Sinclair computers.

I'm thinking of converting one of the 7" LCD monitors to an RS232 terminal using an Arduino as the bridge from the serial communications to the video screen.  I want to investigate how the Arduino interfaces to a 4-wire resistive panel as I've seen details of a library online that looks very straightforward so there is a possibility of a cheap versatile B&W touch terminal here.

Wednesday, 13 March 2013

One Wire is all you need

I ordered up a handful of DS18B20 1-wire temperature sensors and here is one interfaced to my DIY Arduino board.  There are some nice sample programs available to demonstrate the capabilities of the 1-wire (Dallas/Maxim) interface bus with the DS18B20 and this one is outputting the data to a PC via the serial port (USB)

The odd thing beside the sensor is a re-usable plastic ice-cube I'm using to cool the sensor down for testing!

This is the output on the PC via the serial monitor.

The beauty of these sensors is that they can be chained together on the one bus as each one has a unique laser-etched hex serial number to distinguish each one.  This seems to be the way to go for the heating control system as it will have 4 sensors positioned on the water pipes and the hot water cylinder for monitoring.

Friday, 8 March 2013

I Have Wood

Just a quick photo of our ecologically sound recycled wood pile. This is roughly 2 loads, each load being a fill of one of those big builder's sand bag (a big bag, not a big builder, well it might be a big builder...). This should last us well into April hopefully. The wood is heavily compressed chips used to make big industrial pallets for machine parts. It doesn't soak up water much so stays dry under the tarpaulin. Warm and toasty.