Adding some communications coverage
The PIC32 has 6 UART’s, and I am using them all in this project. I was using one of them for a bluetooth module, but could’nt really find a way to utilize this capability for anything smart. Originally, I had planned to allow a user to configure the system through a smartphone app when connected to the bluetooth, but I have already implemented configuration through SMS messaging. With the new WiFi stack, I could also create a simple configuration portal that is served by the unit itself.
So – out with the bluetooth and in with an Iridium satellite modem. Now we’re talking coverage! The Iridium SBC9602 is an amazing little device that supports the so-called Short Burst Data service. It will let me send and receive data through an e-mail gateway to any point on the planet. What is really cool about this is that I now have Geiger tubes from 1973 on the same board as a hyper-advanced satellite modem. Also notice that the satellite patch-antenna is mounted on a ground plane. Transmitting to the satellite network actually posed a new challenge with regards to power – the modem draws 1.5 amps for 10 mS when communicating with the network. I solved this problem by using a 0.22F super-capacitor to be able to supply that much power in a burst.
One additional note since I am getting this questions fairly often: The reason for using ‘old’ geiger tubes instead of more modern semiconductor detectors is to be able to cover as much radiation flux as possible. This is also the reason why I upgraded the project to use two tubes instead of a single tube. Semiconductor detectors have a very small area compared to the tubes, which gives the detector low resolution and sensitivity. If I were to upgrade the detector in any way, I would use more modern tubes. The semiconductor detectors are too small, too difficult to buy, and too expensive. Actually, they don’t seem very available at all. Ebay is full of new-old-stock (NOS) tubes that are both sensitive and cheap.