Nuts and Volts - January 2018

I ended up ordering a micro USB microphone from Amazon which didn’t work too well. The PocketSphinx Python API (application program interface) didn’t recognize the mic, which was due to system misconfiguration. Therefore, I ended up moving the voice recognition to an old laptop I never use that has an awesome built-in mic.

The voice recognition consists of a Python program that uses the PocketSphinx API, which is supposed to send a POST request to the rails server and synchronize the phones, as well as send a signal to the wireless switch. It instead sends a signal directly to the wireless breakout board attached directly to the light for now, and does not work with the central brain of the framework.

As you can see, the voice recognition portion of the project is a work in progress. Getting the speech recognition to be accurate is a bit tricky, too. It works well at the moment, but will need some fine-tuning before it’s fully deployable and ready. I would like to eventually get the speech recognition working on the RaspPi 3, but using my laptop to interface with the lights via voice will have to do for now.

The Switch Schematic and Disambiguation

The schematic of my wireless switch is shown in Figure 7. The wireless breakout board grounds out the BJT (bipolar junction transistor) in this common-emitter circuit and provides a 3. 3 base voltage from one of its GPIO pins (which are the only dynamic and changeable factor on this board and/or circuit). The GPIO pin is either on or off, and this solely depends on the signal coming in from the phone that is controlled by the state of the toggle button.

The board also powers the relay coil with a five volt constant GPIO pin. This board even has a small server written in the C programming language that handles the incoming signals with general C compare functions that have bounds checking.

The BJT is probably my favorite component in this build and by far the most fascinating! Applying the right amount of current to the base and collector of the BJT will allow you to switch high current devices. The breakout board’s 3. 3 volt GPIO pin is what’s used to saturate this small signal transistor.

The 520 ohm resistor at the base brings the current to the required 5 mA, as well as the 30 ohm resistor at the collector that brings the current to the required 50 mA needed to saturate the BJT. All of these factors can easily be calculated by using Ohm’s Law, of course.

The relay is almost an equally impressive device that has a coil that is magnetized once the coil is powered. Once this happens, it closes the armature on this normally-open SPST relay. It surprisingly only takes five volts to power the 70 ohm coil, which again is provided by the wireless breakout board. The other two contacts allow high current to flow through the relay (which is 110 VAC, in this case), but the relay is rated to handle much higher current if necessary.

Once the armature closes on the relay, it completes the extension cord’s circuit and allows power to flow.

Conclusion

Though it was a lot of work, I learned a lot by building this DIY home automation project. Though similar systems are available commercially, I wanted to re-create this particular device mainly because I have a fascination with