Advice on wireless system design & components

[HodgdonExtreme]

Hi, new member here. I'm not even well-versed enough with electronics to be considered a newbie. I'm working on a project that I believe ought to be pretty simple and I'm looking for suggestions on what parts/products to put together to achieve it.

I have 8 analog (voltage) signals I need to transmit wirelessly ~1000ft or so. The plan is to ultimately use a tablet with custom programming to create a GUI/readout.

The ADC will need to be a minimum of 18bit, but 20 or 22 would be better. The signal acquisition speed is not critical, even just 10 samples/second would be plenty.

Additionally, the signals are coming from transducers that require a clean/steady 5-10 VDC power supply, so the transmitting unit will not only need to perform the data acquisition, but provide the excitation voltage for the transducers. This unit will need to be battery operated.

Anyone got suggestions for suitable products I could use to do this?

 

[Arouse1973]

Welcome to EP. This is quite involved for a first project. You will need a micro for sure, I am thinking a multiplexer and a PIC micro. Can you tell us more about your project?
Adam

 

[HodgdonExtreme]

What specifically would you like to know about the project?

I'd prefer not to have to design/build custom boards.

I was thinking a LabJack T7 coupled to an XStream RF modem would be a solid way to go. The T7 unit seems to have a micro that can be programmed to do some basic data signal manipulation and then format it appropriately for RS232/RS485 broadcast via the radio.

I have somebody that is good with C++ that can handle the scripting and then the GUI.

Thoughts?

https://labjack.com/products/t7

http://www.bb-elec.com/products/manuals/9xstreamPKG-R_rmanV42b5.aspx

 

[Arouse1973]

The only question I have is you say you need a minimum 18bit A/D. I don't think the 10 mV input of the Lab-jack is going to be low enough is it? You may need to amplify the input voltage and then do some scaling on it in software. Other than that it looks neat solution.
Adam

 

[HodgdonExtreme]

Actually, I only became aware of the LabJack product recently - which we used on another project that used similar transducers, though in a completely different application. I am working with strain gage transducers. If your'e not familiar, they require an excitation voltage (usually 5-15 VDC), and as force is applied to the transducer, the output of the wheatstone bridge will be higher than the excitation voltage. The output of the transducers we're using is 2mV/V @ full capacity.

Which is to say, if you apply 10V excitation to a 1000lb capacity transducer, when you apply a zero load to it, you'll get an output reading of 0mV. If you apply a full 1000lb to that transducer, you will read 20mV. The 18 bit I specified is what a techie-er guy than myself told me was minimum resolution we needed from our DAQ for adequate accuracy for this project.

The last labjack we used was the U6 Pro unit, which has 3 analog input ranges: +/- 10V, +/-1V, +/-.1V. It worked fabulously. In fact, we used some of the extra analog ins to acquire the excitation voltage so we could use the true ratiometric output of the transducers. Anyway, the T7 unit has the additional input range of +/-.01V. We chose the pro model because it has higher resolution and the project required utmost precision.

The reason we can't use that same U6 Pro this time is, as you mentioned initially, the lack of micro. The last project included a computer that was used to drive the LabJack and handle all the data manipulation. This current project requires the Labjack to work autonomously without the PC to acquire and transmit data to a central unit (computer/tablet) with GUI.