Simple Display

[KenB]

I recently bought a backlit blue LCD from ModernDevice.com, which comes with a small PIC based driver board.

The PIC interfaces, in my case to an Arduino controller via a 3 wire interface (+5V, 0V, 9600 baud serial Tx) and allows the display application to be quickly developed using simple serial print statements.

Commands allow various cursor modes, custom characters, backlight brightness, printing at certain x,y locations and other display effecs to be easly produced.  The PIC has 3 spare output lines which could drive leds or relays etc, or can be programmed to produce an audible beep.

The beauty of this device is not only the speed of application development, but how you can run just a 3 wire interface to the device - allowing applications that need a remote display - such as a solar controller.

My test application shows the time in hours mins and seconds and reads the "temperature" from three ADC channels. This was knocked up in an hour or so - showing how easy it is to get these things working - even for a C novice such as myself.

The display couples to the Arduino with a 3 way "servo" cable.   This implies that various other intelligent nodes could be linked to a central controller using a similar scheme - a little bit like 1 wire.

The photos show the display and the little driver board on the back.



Ken

[KenB]

I've continued development of the simple display, working towards a framework for a datalogging solar controller. 

The system also forms the basis of some related projects.  At this rate I'll have several Arduinos scattered around the house (and workshop) all feedng into a central hub.

I've chosen to use 10K thermistors for my temperature sensors - because they are cheap, I have them lying around and you can get ones that clip directly onto 15 to 22mm pipes.

http://www.rapidonline.com/Electronic-Components/Sensors/Thermal-Sensors/Pipe-clip-temperature-sensors/76422/kw/temperature+sensor

The code currently reads 3 thermistors and a trimmer pot.  The pot is an easy way to set the pump on temperature.  The data from the temperature sensors is linearised and converted to centigrade.  It is then displayed on the LCD and sent to a serial port in a CSV time stamped format.

I am awaiting my new SD card and RTC shield from NuElectronics, and that will be incorporated upon arrival.  Whilst the basic solar controller application is fairly trivial, it's a good starting point to learn how to interface to the various sensors, relays etc and in my case, gain familiarity with programming in C.

In the picture Temp1 is bottom of tank, Temp2 is top of tank, Temp3 is the room temperature of my workroom and the temperature in the bottom right is the "set temperature" which when compared with Temp3 decides whether the pump is to be turned on or not.  Whilst this is not exactly what is needed for the solar controller, it is handy for bench testing before starting to switch real pumps.

The system can be extended to take another 2 thermistors - say panel inlet and panel outlet, and also a pulse generated from a flow sensor, so that the power produced by the panel can be expressed in watts (in real time).

I'm currently monitoring the heat up profile of my hot water cylinder - one application for the controller is to optimise the boiler "top-up" time. This arose from an idea following a discussion with Trystan Lea on the open energymonitor project. 

A pair of buttons on the controller display panel in the living room could be used to select either "bath" or "shower" and then beep gently when the cylinder is at optimum temperature.  A quick calculation would display how long the system will take before an optimal bath can be drawn.  The same system could be used in the winter to choose whether your woodstove/backboiler feeds in preference to the heat leak radiator or maximises the heat into the hot water cylinder.


Ken

 

[KenB]

I've now monitored the hot water tank over a half-hour "top-up" on gas, followed by a half hour cool down.

The results are not quite as I expected, and this simple test may have highlighted a peculiarity in my system - resulting from the way I have my woodstove plumbed into the system.

I have woodstove and gas coupled together by way of a "neutraliser", and then a tankstat on the top of the neutraliser to bring on an additional circulation pump when the neutraliser temperature exceeds say 60 degrees.

It appears that this pump has come on and caused a considerable dip in the temperature of the water fed into the tank coil.  I also think I heard my boiler doing a modulation down cycle approximately 10 minutes after the start of the run - which also appears to coincide with the drop in feed temperature.

This clearly needs further investigation, as I am not getting all the heat from the boiler into the tank and if the heat is being dumped to the central heating loop - then that's not ideal in summer when its 26C outside an inside!

The plot is attached.  The blue trace is the thermistor clipped to the inlet of the tank coil.  The red trace is the water outlet at the top of the tank.  All temperatures in centigrade.





Ken

[2ndBillericay]

Hello Ken, can you post your Arduino Sketch so we can see how you are reading the data from the thermisters and then pushing it out to the Display.

I am looking at this for running my heating pump with a thermister on the tank to top up my solar production in case the system has not produced enough hot water for a shower.

RIchard

[solarbot]

Hi Ken,

Have a look at this site too for Serial & I2C LCD controllers: http://www.byvac.com/bv3/index.php?route=product/product&path=41_42&product_id=100 - I am just starting a project using one - will post more details when we get somewhere with it - the unit has the choice between serial and I2C (we are using the I2C).

Good prices, UK based and nice guy.... on the telephone at least :-)

Nice project you have there - do you have any info on the flow sensor you are using?  I have just spec'd a system using Resol Calorimeters and a DL2 data logger to determine the true CoP on a ground source heat pump (along with an electric meter) - I think the results could be quite interesting :-)

Hope it helps.