If you have followed my blogs you may know that I like to walk at night. During the summer months I always have a small flashlight in my pocket or in my hand. Since I dress in black or dark colors and I am sometimes in the roadway, the flashlight allows me to alert drivers of my presence. It is also useful if my pathway is particularly dark or hazardous. I have previously made a boot light https://www.element14.com/community/people/jw0752/blog/2019/08/01/walking-in-the-dark which has greatly lessened the need of a handheld flashlight. None the less I like to have the handheld light available.
As the weather has turned colder and I have had to start using gloves the ability to manipulate and turn on a flashlight has become an issue. I am always looking for ways to solve situations like this with technology and this seemed to be a perfect time to build a wrist mounted voice activated flash light.
I had been gathering potential materials and making and discarding ideas for about a week before I started the actual build. The flashlight that I had decided to use was an LED type sold by Harbor Freight and cost $10.00.
This is a beautiful little flashlight with Zoom focus of the beam and three light settings, Bright, Dim, and Strobe. It does however have a dark side. It is powered by 4 AAA batteries (6 volts) and my tests show that when the flashlight in on the bright beam and powered by 6 volts it draws 1.5 Amps. Anyone familiar with AAA batteries knows that 1.5 amps is not a sustainable current for these small batteries. Since I did not want the flashlight to die during one of my walks and I certainly did not want to be buying AAA batteries frequently I would have to find an alternate power source.
The ideal power source would be a lithium ion battery that could handle the 1.5 amps for a reasonable time as well as being rechargeable. I decided to use a couple 18650 cells that I had salvaged from a laptop battery pack. The two Lithium batteries in series would give me a nominal 7.4 volts which would be too high for use on the flashlight. I would have to have a way to bring the voltage down using a DC to DC converter. In the meantime I had performed additional experiments on the flashlight and I found that by using 5 volts the light output of the flashlight was still excellent and the amperage had dropped to 1 Amp.
I experimented with various voltage regulators and circuits before I decided to use a nice adjustable circuit with a digital voltage readout. This was a circuit board that I bought off the Chinese market a while back. It has an offset of 1.2 volts and can handle 5 amps of output current.
The circuit has 2 key switches that allow me to turn the display on or off and I can choose to monitor the input or output voltage. In the picture above the circuit is monitoring the 8 volt input voltage of the 2 Lithium batteries.
I also decided to use a couple of super capacitors to stabilize the output voltage. Bench tests had shown that glitches caused by switching would interfere with the proper operation of the voice activation. I used two 40 Farad caps in series for a net 20 Farad 5.4 Volt capacitor bank. The capacitors were about the same size as the batteries so the fit nicely into the battery area of my device.
The voice control for the flashlight would be provided by a circuit that once again came from the Chinese market several years ago. This is a simple transistor bi-stable flip flop circuit with a microphone input. You have heard of the commercial variety of this circuit as a "Clap Switch".
The clap switch circuit would sense the noise of my voice and turn on or off. I would use this output voltage level to control a MOSFET which in turn would power the flashlight. I ran bench tests to verify and refine my plans.
Since the voice activated flashlight was starting to look very techy I decided it would not hurt to add one more feature, an indoor / outdoor thermometer. I could use the indoor side of the thermometer to read the outside temperature as I walk. Here in Wisconsin in the Winter this can range from 32 F (0 C) to -20 F (-29 C). It actually gets colder than this but even with good winter gear temperatures below -20 F are too dangerous to walk just for the sake of it.
All my life I have suffered with my feet getting too cold in the winter. As a kid I would often suffer from chilblains after coming in from play. Now I have some really good boots but still the potential is there for this painful condition or even worse the prospect of frost bite. If I thread the outdoor sensor of the Indoor / outdoor thermometer into the toe area of my boot I will be able to monitor just how cold my toes are getting and I will be able to take some remedial action (like calling the wife to come a rescue me) before things get too bad.
The next step was to put it all together and build the wrist mounted, voice activated flashlight, with thermometer. This is what the finished first prototype looks like:
I am using velcro straps to hold the unit to my right arm. When strapped into place it positions quite well and allows me nearly full use of my right hand. I can bring the unit within a foot of my mouth and turn the flashlight on or off with a voice command or more dependably, because of my weak voice, a click of my tongue. I have made a video of how the unit works and in the video you will see it ignore one of my voice commands to turn off. I would have redone the video but my videographer (wife) had to leave and so you will get to see an honest demo video. It appears in the video that I am telling the device to turn on the bright, dim, and strobe features of the flashlight but these features are cyclical and I am just telling it to do what it is automatically going to do anyway. Here is the demo video:
So now I have this wonderful voice activated flashlight with thermometer and I am eager to go out for a walk and try it out. However I can't.
Both my wife and my daughter were quick to point out that when it is strapped to my arm it looks like a gun. This perception will be even more pronounced as I walk through the darkened streets of my city. Someone will call the cops on me an when they pull up and surround me with their guns pointed I will stand there with my flashlight and my hands in the air. They will tell me to drop the weapon but since it is velcroed to my arm I will not be able to. My poor voice will not be loud enough for them to hear my screams of Flashlight! Flashlight! over the noise from their patrol cars. When I do not comply and drop my flashlight there will be a hail of gun fire and I won't be able to bore you with any more of my curious builds. It seems that I have designed myself into a corner.
When I have time I think I will down size the idea and use a smaller flashlight, get rid of the need for a DC to DC switching convertor, lithium batteries and the thermometer will also have to go. If I can get the Clap Switch to run on the flashlight batteries it is possible that I will be able to make a unit that is small enough to still be useful and not get me into trouble with the law.