analogue data to ascii and back

[ringo2143z]

Hey all,

I'm a 4th year Aero Mechanical Engineering student, and for my individual project this year I'm trying to come up with a tension monitoring RF system to be used during a glider/sailplane winch launch. My original scope was to make an alarm system which I have working using simple RF modules and it's all good. Unfortunately, my supervisor now wants me to look into datalogging the tension in the wire and that's going a little bit beyond my electronic know-how. I have the ER400TS, ER400RS and ER400TRS modules from Easy Radio ( www.lprs.co.uk ) which are apparently modems although the datasheet I had said they could send RAW data. Never mind.

Anyway, my issue is that the Easy Radio kit will only send ASCII according to the company . I need to somehow convert my amplified analogue signal from my strain gauge bridge into ASCII, transmit it and then convert it back into data that I can graph at the other end. Anyone know how to do this?

I've been googling and hunting through Farnell/Rapid/RS websites trying to find an interface that might do this but haven't so far. I believe there's probably a microcontroller route I could take but I don't know enough to program them to do what I want.

Cheers!

[CeeBee]

The microcontroller is the way to go, you can then program the sampling rate and data format the way you want. I have used in the past some PIC microcontrollers, they also have a new line of RF products. Good part is that learning how to code even in assembler (my prefeered way) is not that difficult, but most manufacturers provide BASIC or C compilers for their products. If you have some flexibility you can also look at solutions from TI - especially their DSP-capable microcontrollers - this way you can do some FFT processing on-the-fly and provide a more acurate reading (ex you can then detect vibrations that would otherwise be ignored since the analog level gets averaged for A/D conversion.

[ringo2143z]

Thanks for the reply CeeBee!

I'm probably limited in what I can spend on a microcontroller since I've already spent a good £160 on RF kit and components here and there. Do you have any specific model recommendations for the analog to ASCII conversion I desire?

I looked at both the brands you mentioned but I'm unsure which models will do what I need. I'm very new to this area and the last time I touched a microcontroller it was in Technological Studies in high school with, I think, pbasic programming (although it was just copying out of a book) and they weren't fancy by any means.

[CeeBee]

As a matter of fact you have very many options, you have to choose something that suits your purpose and *you* can program with minimal effort. Some of these microcontrollers are dirt cheap ($5..10 for qty of 1...).
For example PIC16F7x series has some 5 A/D converters with 8-bit output, RS-232 I/O, 20MHz clock... all for less than $8 at www.digikey.com
Probably you'll have to spend some $50 for a programming kit but that's a different story. The thing is that the possibilities are countless, your imagination, time and skills are the limit. BTW, these PIC's are RISC uC's so you are getting extreme speed here... 1 instruction/clock.
So you can program your own timer, when it expires generate an interrupt, read the output of an A/D converter, convert to ASCII with your own routine (hint: sepparate the upper and lower 4-bit groups, convert 0-15(bin) to 0-F(asc), concatenate the 2 characters and output.