Mobile Texting Safety Device

Mrs rog and I were walking our dogs recently and were standing, waiting for them to sniff whatever it was that needed a good sniffing and a young lady walking up behind us, engrossed in her phone, would have bumped into me had I not noticed her and stepped aside. As we walked on I said to Mrs rog that there should be some sort of anti collision device that could warn a mobile texter that there was something in front of them.

A day later I had breadboarded a possible solution. I decided to use an Arduino nano, a HC-SR04 ultrasonic module and a small piezo sounder (which I later dropped).

The arduino sketch is pretty simple, I have uploaded the final version where I have set pins to supply the ultrasonic module directly as described later in this build.

The distance for object detection is settable as is the length of time the motor runs on detection.

Arduino Nano without headers

HC-SR04 ultrasonic module

3.7v lipo drone battery(this one comes with a charger)

DC to DC boost converter 3.7v to 5v

Vibrating motor 3.7v

Small slide switch

NPN transistor

IN4001 Diode

1K resistor

3D filament printer

M2 cap screws and nuts

After breadboarding my thoughts I went on to tinkercad a casing that could hold a credit card sized usb power pack that I had knocking around. A piezo buzzer, a small vibromotor unit and a slide switch to swap between them were all tinkered in as was a USB connector to plug in the power pack.

A good space saving idea came out of this, by making pin D4 always Low and pin D7 always High I was able to solder the ultrasonic unit directly through the pin holes on the nano stacking it on top.

I don't propose to go too deeply into this model as it revealed the following problems that would be addressed with the more fully detailed build below.

Problem 1 My battery pack would not stay switched on as the current draw in standby was insuficient to keep it on.

Problem 2 The vibromotor was too gentle, and would be difficult to feel.

Problem 3 The size of the finished unit was way too big to be worn on a hat or a headband....

Before I designed the case for the above I went into tinkercad and blocked in all of the components I want to use in the build, I added 0.2mm to every dimension on each of them to ensure a good fit when they were turned into holes in the design. This became invaluable when I did my redesigns as most of the parts were already detailed.

The battery first time around was way too big so I decided to look at camera batteries, I already had a spare pack and charger for a fuji NP-45 so I decided that would be the one to use!

It made sense to copy the housing in the charger to fit the battery but it leaves me needing a pair of contacts to get the power out, I had one of the very cheap twin cr2032 battery holders with LED string, I sacrificed it for one of the contacts it contains.

I found a 3.7v vibrating motor that is far more vibratey, it draws more current than the arduino can provide so I needed to make a small circuit with a 3.7v to 5v converter driving a PNP transistor and a flyback protection diode across the motor. I should have tested the motor more thoroughly........

That went well, as it turns out it still looked big and ugly on the hat and the vibrations would have rattled out the teeth of anyone wearing it!

I tried again with yet another motor this turned out to be a goldilocks motor being "just right".

The only bit I got right first time around was the 3D printed base for the device which I attached to the cap peak with a pair of M2 x 20mm long cap screws.

Having found a smaller battery, a smaller motor and a smaller NPN transister, it allowed me to make a much lower profile two piece housing.

The two pieces are held together with M2 x 16mm screws and nuts, as the nuts are deeply recessed I printed a tool to aid assembly which holds a nut in place to get it in position to be pulled into the housing where it is trapped.

There is a recess for a magnet in the removable piece and I slipped a thin piece of steel strip inside the caps headband in the correct position to be grabbed by the magnet which keeps everything in place on the cap.

Once the new housing was printed I was able to cut the piece of vero board to fit the recess. The slide switch is soldered directly to the veroboard and locates the circuit in the housing.The little DC-DC converter gets soldered on after all the wires are attched as access is limited once it is mounted.

The whole of the electronics can be assembled outside the housing making it simpler to work with, it is a tight squeeze but it all fits....but does it work?

The assembly fits quite well to the shape of the cap, it sits tilted up so it detects things above normal eye level when walking looking ahead but when looking down at your phone it will give you between 1m and 1.5m warning that there is an obstacle ahead. I tried walking with the camera held beside my head in the hope it would pick up the sound of the vibramotor, it couldn't as I live near a very noisy road. The best I could come up with is a short video of it on a wig stand in my kitchen! You can just about hear the motor above the traffic noise, wearing it is very different, no matter how noisy the environment the vibration is easy to feel.

I started this on a whim, as my bio states I build things where "the idea popped into my head". I cannot see anyone using something like this to enable safer "walking whilst texting".

I had three goes at it to get it as small as I could, what would I do differently?

I would cover the electronics rather than them being exposed when the assembly is removed from the cap.

It occurs to me that the design could be made to look like a pair of sunglasses perched on the cap.

It has also occured to me that it could be useful for someone with limited vision.

That is for someone else to do, I have my next project to work on :)