Honeywell Magnetometer and 2.4GHz transmitter RFI/EMI issues

Wireless & IoT
1

I’ve been working with the nice new Honeywell HMC1052L dual axis magnetometer chips, and they’re giving really nice data. That is, until I started transmitting the data using a bluetooth radio link. It seems that the radio frequencies from the bluetooth antenna are contaminating the magnetometer readings, generating huge spikes whose maginitude depend on the proximity of the radio antenna.

I’ve tried all forms of sheilding - faraday cage works well, but I need a perfect shield, and the only perfect shield in tests is a completely sealed sensor (inside of antistatic 3M bag material). Unfortunately, this is not a good or convenient solution. Also unfortunately, the sensor module is so small that physical seperation of the magnetometer chips and the RFI source is not possible. Even an external duck antenna generates RFI in the shielded sensor module box.

I’ve become so frustrated that I’ve decided to move the transmitter to a seperate module.

Any ideas on this?

2

can you arrange things so that measurements are not made, or are discarded, during RF transmissions?

Of course, you’ll want to try to get the antenna a foot or two away

3

Thanks for the reply Steve - it’s a bit tricky with the Bluetooth protocol… The master sends out frequency hopping commands, and expects responses. Also, if packets are lost, they’re retransmitted. So sometimes there are transmissions even when I might not expect them.

It’s a good idea though. I’m still trying things out to see if I can get around the problem. Most likely, however, I’ll just go with the external antenna (like you said, foot or two away).

Ah, RF.