Vorticon's Blog - Wireless weather station managed by the TI 99/4A

RSS Bot · December 30, 2016

So it's time for a new hardware interfacing project for the TI 99/4A, namely a wireless weather station managed by that venerable computer. I think it will be a fun project but likely with a steep learning curve. The goal is to have a functional prototype in time to demo at the 2017 Chicago Fair.

So where does one start? The most obvious would be finding a cost efficient and relatively easy way to achieve wireless communication between the various sensors and the computer. I believe the Xbee series 1 modules fit the bill quite nicely because they have a range of about 90 meters (300 feet) which is more than enough for the average user and they come pre-configured for serial communication. I chose the version that has a connector for an external antenna in order to maximize the transmission range.

These modules have integrated ADC as well as digital inputs and transmit data serially which can be captured by a sister Xbee module connected to the computer. Unfortunately, they would not be enough by themselves because there are few sensors that can interface directly with them without some sort of processing first, and so a microcontroller is going to be needed for support and data packaging within the sensor array. With so much community support and experience available for the Arduino, I decided to go with the Arduino Uno using the Sparkfun Redboard.

It comes with installed headers and connectors, making it easier to access and interface.

Now for the sensors:

While I could design and build my own mechanical components for wind speed, direction and rain level, it would be a pretty laborious process. So I opted to go with a ready made solution that is super easy to interface, again from Sparkfun:

This is a purely mechanical device with no embedded electronics, and the data interpretation is via checking the state of various switches. What is even better is that it has a direct interface with the Sparkfun weather shield for the Arduino Uno which also includes pressure, humidity and luminosity sensors.

All we need now is a temperature sensor, and the one below is inexpensive and pretty easy to use. It is analog, so it will be earmarked for one of the Xbee ADC inputs.

This should round up the sensors for our weather station. The last thing we need is the Xbee serial explorer board to connect a receiver Xbee module to the TI 99/4A via the serial port.

So far, this is going to cost around $215, and will likely need another $25 for various connectors and support items. So no, it's not exactly cheap, but the fun factors of putting all this together will be priceless!

Now what? Well, first of all I'm going to have to get familiar with the Arduino since I have had zero previous exposure to it. I have always used the Raspberry Pi for my other projects, but it would not have been suitable for this one. That is going to take a little time. But even before that, I'm going to have to dig deep into the Xbee documentation and come up with some communication tests, likely using only the temperature sensor for starters since it can connect directly to it, and see if I can transmit data wirelessly to the TI.

Stay tuned