Wireless data xfer with moving TX source

Wireless & IoT
1

Can anyone recommend which of the Sparkfun wireless solutions would work best for my application. I only need to transmit at 1200 baud and at distances of 10-15 feet, but my transmitter is attached to a person’s arm, and thus moves around a lot.

Preliminary testing (using TLPA/RLPA 315 MHz) shows a clean signal received until the antenna on the TX travels through the perpendicular to the RX antenna. Then the signal gets disrupted. Which unit do you think would be best for a moving TX like this application? Or is there a different TX antenna configuration that would work better?

Thanks,

Chris

2

All RF links are going to drop data. You’ll need to take care of as much as you can with firmware.

Or course I would recommend using a nRF module like the MiRF or the RF-24G. Higher freq. means a bit less susceptibility with antenna problems.

-Nathan

3

You are right. Indeed, the 916MHz Laipac was much more stable than the 315MHz in terms of seeing the transmittted signal as the transmitter was moved about. I’ll be trying the Blue Smirf to a) save development time on getting reliable data transmission and b) to permit having two transmitters and one receiver (my application has a transmitter on each arm).

Hints for other Laipac 916MHz users:

Getting the 916MHz version operational was a bit more of a challenge. It is not clearly pointed out in the data sheet (if you can call it that), but the data input for the transmitter should apparently transition between 0 and 1.5 volts. Not through the full Vcc voltage as with the 315MHz unit. (The 916 application sample circuit suggests this, but the tabular data does not) I had to adjust the variable cap on the transmitter to get all data bits to appear on the receiver, and I’m still getting a few extra bits when I finish transmitting a block of data. Perhaps a side effect of the FSK?

Chris

4

Hi Chris,

Since your application seems similar to what I am trying to do, quick question.

Did the 916MHz Laipac’s turn out to provide the solution for you?

Did you test anything in 2.4GHz.

Thanks,

Serge