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Stephen Coates
10th December 2007, 20:48
I finally got round to copying a programme from a book into the BBC which will draw a graph which depends on the light or heat going into an LDR or a thermistor connected to the analogue port (why don't PCs have analogue ports bult in so you can do cool stuff like this?).

It draws the graph from the left hand side of the screen to the right, over a period of about 5 seconds, then clears the screen and starts again.

Does anyone here know of any software which can be used to draw graphs over set periods of time, and then save/print them? And preferably give values in celcius?

It isn't possible to do this at the moment with the programme from the book as all it does is look at the voltage going into the analogue port and has no way of determining what the temperature/brightness is. For the graph, I could probably set it to spend longer drawing the graph, and therefore maybe have a graph for an hour, rather than just a few seconds, but that doesn't help with the units or printing.

An additional device may be required, but I would still be interesting in finding the device and some software which would do this. I know such software exists as we were shown these things on the BBCs in school a couple of years ago.

J T
10th December 2007, 21:38
We too used a BBC in school to do an experiment on latent heat of evaporation or something like that. I have no idea what the software is though. Have you tried asking on a specialised BBC board, or even a teaching/education/science board?

As for your temp question - If the y-axis is always a value of voltage and of the same unit scale/range you can do a quick (relatively crude) calibration by using some boiling water for ~100 C and some ice for ~0 C, mark these on every graph (may have to be done by hand on a print out or trace) and can work out the temp at a given point using a ruler and measuring the distance between these boundaries and a spot of maths. Far from ideal though, but maybe there is a way to add code this into the program - but I wouldn't have much of a clue as to what code to use, mind.

Not much help for the brightness probe though.

Stephen Coates
11th December 2007, 10:32
I would need to adjust the resistors used for temperature, as currently, I only seem to get values of between 10 (for outside at night) and 70 for 2 inch away from a 60w light bulb.

So it isn't really measuring anything that accurately (you can hardly see a difference on the graph). The light sensor makes use of the full 0 - 1024.