New Accessories for the AirChrony S3

With the increasing abilities of AI it has become so much easier to take an idea to a finished, working item in a really short time.

I was thinking about the next teps for the AirChrony S3 and I had two ideas, an addon battery holder so that I didn't need to plug it into a USB powerbank and a remote monitor so that I could use it without my phone.

Addon Battery Carrier

I wanted to be able to have the option of using the USB powerbank or a dedicated supply that attached to the Chronograph, to this end I designed a sleeve that slid over the chronograph body and secured it using the the existing screw.  The battery slot was sized for an 620mAh LP602248 Li-Ion rechargeable pouch cell.

3D Render of the battery Sleeve

Actual assembled device

Sectional View from the Right Side

Due to the fact that the IR Detectors require a 5V supply to operate reliably I needed to supply 5V to the Xaio ESP32 rather that include a cell inside the device so I used a DC/DC step-up converter to increase the 3.7V cell voltage to 5V, the buck converter was very small and had the same connection pads as a USB C PCB connector I had and they soldered together perfectly, I soldered on a 2mm PH JST socket to the DC/DC conveter input to connect the batery to then slid the whole assembley into a 3D printed sleeve that fits into the USB connector entry of the Chronograph.

USB C Plug/DC/DC Buck Converter Assembly

 The above assembly in the 3D printed Sleeve

Remote Viewer Screen

The second accessory was a remote viewing screen that would connect to the Chronograph instead of the mobile phone and allow the viewing of the shot data and other functions.

I had an ESP32-S3 based display module that I'd bought from Aliexpress, this had a 2.8" capacitive touch screen, speaker output, battery charging circuit and SD card slot.  I designed an enclosure to house the display, speaker and an 1100mAh Pouch cell.

Whenever a shot is registered the display will beep (optional).

3D Rendering of the case

Actual Screen Layout

All the code for the display was written using Gemini Antigravity AI in a couple of hours, it's stil a work in progress with more functions to be added but so far it all seems to be working.

When I'm happy with the final version I'lI will post all the files/code on my github www.github.com/gadjet

Latest Version of Chronograph - AirChrony-S3

Update on the Latest version of the DIY Chronograph, the PCBs have arrived, I've populated them, assembled the chronograph and done some basic testing, so far so good.

All design files can be found on Github at www.github.com/gadjet 

Detector PCB

Emitter PCB

Top View with Xiao ESP32 S3

3D printed case parts

Also, to help assemble the detector and emitter PCBs with the detectors/LEDs I made a helper jig, this makes sure that the distance between the lenses on the detectors/LEDs are spaced exactly 50mm apart to match the tube.

Jig usage

DIY Chronograph Revisited

This project is still a work in progress as I am waiting for PCBs and parts to be delivered, so details like the 3D-printed enclosure and software will probably evolve. I will create a GitHub repository once I am happy with how everything is working.

It has been over 10 years since my first blog entry on my DIY chronograph (https://gadjetsblog.blogspot.com/2013/02/air-rifle-chronograph.html), which used an Arduino Nano and a Bluetooth transmitter. That setup connected to an app on my phone and transmitted the elapsed time between trigger 1 and trigger 2. The app then used that time, along with the entered pellet weight, to calculate the muzzle velocity and kinetic energy of the rifle/pistol.

I have built a few projects since then. Although I enjoy designing hardware, writing software is not my strong suit. Like many others, I have started using AI—specifically Google Gemini—to help write code not only for the microcontroller hardware, but also for the web-based user interface.

I realised that I could modernise the DIY Chronograph using an ESP32, my favourite being the Seeed Studio XIAO ESP32-S3. Running at 240 MHz, it is substantially faster than the older Arduino Nano. Because it features built-in Wi-Fi and web server capabilities, the entire user interface can now be hosted directly on the chronograph itself. You simply open a web browser on your phone, tablet, or laptop to interact with the device.

Hardware

The core concept remains similar to the original design: two optical IR emitter/detector pairs are spaced 50 mm apart, creating two infrared beams. When a pellet passes through and breaks each beam, high-speed hardware interrupts measure the travel time across that 50 mm distance to accurately calculate the projectile's velocity.

 

The outer casing is printed in two halves that slide over the electronics and aluminium barrel tube. They lock securely together using two 2 mm alignment dowels and an M3 screw.

One interesting challenge was "how to package the FPC antenna" this proved to be a bit tricky so in the end I went for a single wire antenna 31mm long.

This solution allowed me to feed the antenna back into a hole inside the casing and it works perfectly well in the 2 or 3m range needed to work with your phone.

Power is currently supplied via a USB-C cable from a 5V power bank, with the option to add an internal LiPo battery later. *(Note: The USB-C connector head must be slim enough to fit into the 11.5 mm × 6.5 mm housing recess).*

Unlike the original design, where raw timing data was sent over Bluetooth for the phone app to process, all calculations are now performed locally on the ESP32. 

To view the live dashboard, simply connect your phone or PC to the **"AirChrony-S3"** Wi-Fi access point and navigate to **`http://192.168.4.1`** (or `http://chronograph.local`) in your browser.

User interface

When opened, the dashboard immediately displays the **"Live Chrono"** tab showing the latest shot's speed, muzzle energy, rolling averages, and a velocity progression graph. 

Additional tabs include:

• Pellet Profiles:** Save custom pellet profiles with brand names, calibers, and weights (in grains or grams) to automatically calculate muzzle energy (Joules or ft-lbs).
• Saved Strings:** Store, recall, and export previous shooting sessions directly to CSV or JSON from the ESP32's onboard flash memory.
• Settings & Diagnostics:** Customise speed units (FPS / m/s), toggle between dark and light themes, configure sensor spacing, test beam alignment, and enable spoken voice callouts (e.g. shot count and velocity spoken aloud through your phone or Bluetooth ear defenders).

The project is constantly evolving as new ideas arise, and you are welcome to use AI to tailor the firmware and interface to your own setup!

DIY Chrono Mark II

Latest project update for 2026 here

Well it's been a long time since I started off this project and I've made a few changes along the way and a few people have had a go at making their own Chronos based on the entries in this blog, some followed the design and some incorporated elements of their own into the design to improve it.

Chrono Mark II Assembled

There were a couple of the things I wasn't keen on with my design: -

• The fact that it was not a round tube but a teardrop and therefore may not always line up with the rifle and look a bit odd.
• An external charger circuit was required to charge the internal battery.
• The switch was mounted at the other end of the tube from the electronics and was a bit of a pain to wire up and assemble.

So along came the Mark II with the intention of improving on those issues.

The main reason for the teardrop design was to fit in the electronic modules with the central tube so I needed to come up with a design where I could place the modules and battery around the perimeter of the tube whilst keeping the overall diameter as small as possible.

I also wanted to add a charging circuit inside the tube so there was only one part to worry about so you could just plug it into a phone charger to charge it.  If I could get all this inside the tube, along with a switch located at the same end as the electronics then it would be a big improvement IMO.

First test was putting the modules around the tube .... using Tinkercad I messed around with all the modules trying to fit them in.

 

Having got them to all fit in a round base I set about figuring out the charging the battery and powering the Nano from the 3.6V battery as the IR receivers were specified to use 5V.

After a good Googling around for some modules I finally found some modules that fit the bill, one to convert 3.6V to 5V and another to charge a single lithium cell from 5V.  These module need to be pretty small and I wanted them to be on a single PCB to make wiring up the modules easy so I designed a PCB to mount them on and had the idea to attach the PCB to the switch which would be securely screwed in to the base.

Power PCB Circuit

Design layout

Final PCB

The outcome for this design means that when switched on the 3.6V battery is connected to the DC/DC converter supplying 5V to the Nano, BT module and the IR beams, when switched off the battery changes to the output of the single cell charger module, which gets it's 5V supply from the nano USB connector therefore charging the battery.  Also all the supply connections for the modules are also on the PCB making it easier to wire up when assembling.

Some More Images

 

Things you'll need

Item	Link	Cost
Pololu 5V Step-Up Voltage Regulator U3V12F5	Link	£3.32
DD08CRMA Mini 5V 1A Lithium LiPo Charger Module	eBay Link	£1.97
Mini Miniature On/On 6 Pin Slide Switch DPDT	eBay Search Link	~£0.40 ea.
Power PCB gerber files	Link	£0.00
3D Print files for carrier and tube	Link	£0.00

New Android app for the Chrony F1

I recently bought a damaged Chrony F1 from a chap that had accidentally shot it, it never ceases to amaze me how companies can design and sell things that by design you shoot at and not put adequate protection in front of the delicate electronics.

The front casing had been hit and had a large dent in it that cracked the LCD and dented the crystal body, after a suggestion from John on the Facebook group "SHOOTING CHRONOGRAPHS U.K." I looked at Radio spares for a replacement and bought this screen 184-7715, it worked like a charm and after a bit of panel beating and a lick of Hammerite Dark Green paint it looked as good as new.

Before and after

One other thing I did before shooting at it was to buy some 10mm Acrylic sheet from eBay to make some clear shields to protect the display and the rear sensor block.

So when I started to use it I realised that I'd have to write down the readings and calculate the power myself later ..... s*d that! surely there's an app for that, if not I'll write one.

So I created an app to record the readings after each shot with the option to speak the value if you prefer and automatically calculate the power using the pellet weight you entered.

I also learned of a secondary Android market called Aptoide, to which I added some of my apps so they can be downloaded from one place.

The link to my store is http://gadjetware.store.aptoide.com/ there are other apps there as well, if you think it's worth it buy me a beer using the beer icon :-) and I might add more features.

I found the serial communication protocol for the Chrony F1 and when I get a chance I'm going to look into adding the Chrony remote functionality to my PC software and maybe make a Bluetooth interface so your phone can talk to it.

Updated PC software for the DIY Chrono (and Combro)

Just a quick update for anyone that has tried the PC software application for my DIY Chrono before, I've re-worked it a bit and changed the layout and moved the settings to a separate screen.

Also now I've fixed the Combro option not working so it should now report the correct values, if not please let me know as I don't own a Combro ..... the whole point in making my own.

Some Screen shots ...

Main screen interface

The main screen shows all the shot details in FPS and M/S along with a min FPS, max FPS and a Delta FPS.

On the right there is a list that adds each shot's data to a row so you can see the history.

At the bottom is a chart section that, if the checkbox is checked, shows the data graphically, there is a tab for FPS and one for energy.

You can also select the option to store the shot data to a file on the PC, the path is set automatically but you can type in your own.  The data is stored as a CSV file and can be opened by excel and used to create a graph.

Settings screen

The settings screen is self explanatory, I hope, change the settings and they are stored for next time, the pellet data etc. is stored in the CSV file as well.  If you have a Combro then tick the checkbox and the software should work for you as well

Here you can set the PC to make a noise

You can set the PC to give you an audible warning every 'n' shots, this is good for knowing when you fired your last shot and you're not looking at the screen, the other check box resets the shot count after the beep.

You can download the file from here unpack the rar file and run the setup to install.

Comments and feedback always welcome and if you like buy me a pint with the donate button.

Chronograph completed - Finally

Latest project update for 2026 here

As anyone who's read this blog before will know, there's a common theme throughout, the DIY Chronograph I made for measuring the speed of an airgun pellet.

Well since getting a 3D printer I've finally managed to finish off the project and put it in a case, it's not often I actually put things in a nice case.

The first case with the Nokia display, it was a bit clunky and easy to break, when I dropped it that is!

Second attempt, this is the one I've been using.  This one uses the Bluetooth module to talk to an app on the phone here

Collection of bits held together with heatshrink

The final one, this one contains all the gubbins from the shot above inside the cover.

The end that screws on with the USB connector below and the front
view with the on/off switch and battery charge connector

Side View

This one uses the Bluetooth adapter and connects to an app on the phone and has an internal lithium Ion battery than can be recharged using an external supply and charging module, you can leave out the battery and use the USB connector of the Nano to power the chronograph from your laptop or a battery pack with a USB power output. (if you do this then the switch doesn't do anything)

The enclosure is essentially two parts, a carrier, that holds all the electronics and a slide on cover.

Both parts are a push fit onto the aluminium tube (16mm Dia. x approx 100m long)

Parts list: -

Item	Source	Approx. cost
3D printed enclosure - Thingiverse	www.3dhubs.com www.shapeways.com	£10 - £20
Arduino Nano (could be mini pro etc.)	Ebay	£2
Slide switch	Ebay	£2
Battery (Turnigy Nano-Tech 600mah 1S 3.7v 35-70C Lipo E-Flite)	Ebay	£5
Aluminium Tube - 16mm OD	Ebay	£5
Bluetooth Module	Ebay	£4
3V to 5V converter (NCP1402-3.3V STEP-UP BREAKOUT)	Proto Pic	£4
JST wired plug connector	Ebay	£3 for 10 off
IR Emitter x 2	Ebay Farnell RS Components	RS= £2.25, 5 off
IR Detector x 2	Ebay Farnell RS components	RS=£5, 5 off
Arduino Sketch	Here	Free
Android App apk file (from Aptoide store)	Here	Free

So around £44 to put together, £24 'ish if you can 3D print your own enclosure.
You could also do away with the battery and 3 to 5V converter if you powered it from you laptop USB or battery with a USB socket on it.

More images

Battery and PCB modules in place with the tube

Barrel end showing the USB connector

Front end showing on/off switch fitted

Inside the cover

The Bluetooth module wired to the Nano

Nano and BT module in the carrier

Everything wired up... nearly. 3 to 5V converter top left under the battery

Tried and tested and working OK, the app works fine and I'm looking to add a graphing function so you can see the performance over a string of shots.

Fritzing schematic

As usual feel free to ask questions and comment below.

DIY Chronograph - Nokia display

Latest project update for 2026 here

The Acrylic case arrived on Saturday for the Chrono using the Nokia 5110 display.

I just wired up the display to an Arduino Mini Pro and put the case together to make sure it all fit together.

The Nokia display is on top, the battery on the bottom with the Arduino Mini Pro in the middle.

No I have to fashion a joystick extension, sort out a power switch, build up the sensor tube and figure out to re-charge the battery with out taking it all apart.

Sketch can be downloaded here.

Sketchup and EPS files for the case are here.

DIY Chrono Shopping list

Latest project update for 2026 here

A few people have expressed interest in making a DIY chronograph so I said I'd put together a shopping list.

There are quite a few options for the display type so I try to give the pros and cons at each step.

Firstly, the processing power.
All my projects are done using the Arduino family, including the many clones out there, I've used original Arduinos and Clones from China all without any problems. (A PIC Micro will do just as well with the same hardware)

Arduino Mini Pro	Arduino Nano
These are available in 5V 16MHz and 3.3V 8MHz versions, I used the 5V versions @ 16MHz to get the best uSecond resolution, I believe that the 5V versions can be run at 3.7V and still run at 16MHz. This device needs an external USB to serial adapter to allow programming but, once progr ammed, can be fed from a 7V source via the on-board regulator (RAW input) or a regulated 3.3 to 5V supply on the VCC pin. I bought mine on Ebay from here for less than £3 but it took 27 days to arrive. Others on Ebay search	These are the boards I've been using, mainly due to the USB connector for both programming and supplying 5V.  I use an Eveready unit that uses 2x AA batteries and steps up the voltage to 5V, I connect this with a standard micro USB lead. Apart from the on-board USB and the in-circuit programming connector (far right) the specs are the same as the Mini Pro. These can be bought on Ebay for around £4 from China and around £10 from the UK, they're a little more expensive due to the on-board USB. Ebay search.
Display Options
This is the top of the range display £7 from China but has the advantages of being colour and also touch screen. I didn't go very far with this display but I think it would be good in a larger Chronograph that has a large detection curtain.
	This is an I2C connected display and can come in yellow, blue, white and red. This is my choice for my portable sensor. It's very easy to program and is a similar size the the sensor tube so is a good fit, see this post. You can only really display one value, I chose FPS because that doesn't require you to input the pellet weight, you can generate a little look up chart for you pellets.
I dug out an old Nolia 5110 phone display that was set into an Arduino UNO shield and added it to the DIY Chronograph family, it works pretty well and has a very good contrast for outside readability and the 5 way switch at the bottom centre allows for a menu system to enter the pellet weight. I can't get the shields any more but the screen can be bought off Ebay for a couple of quid from China and around £7 from the UK, these displays not on the shield work on 3.3V only so require some level shifting when used with a 5V arduino.
	A cheap and cheerful display that can be bought in many webstores an Ebay, they're nearly all the same connection standards and have Arduino Libraries readily available and can come with or without backlighting.
Similar to the 2 line 16 character display just a bit smaller, easier to package and can come with and without backlight, the non backlight versions tend to use an LCD technology that means they're a good contrast  and can be good in sunlight.
	Fancy using your Android smartphone as the display then this is what you need, available from £5 in China to £15 in the UK. Be careful, this board comes with and without the back PCB, without it is a bit fiddly to use and works of 3.3V only. Ebay search
Other parts
	I chose Aluminium tube because I wanted to thread it to fit my 1/2" UNF silencer adapters on my rifle and pistol but you could use any tubing you liked, depending on how you want to fix it. I bought mine on Ebay from here. You will need to get it cut to length and threaded if you want to do as I did. Maybe you have an old silencer that you could modify.  See this post for assy. details
The sensor LEDs were bought from RS components, they are available on Ebay but at a huge markup Photo sensor - OPL-550a Ebay Farnell RS components IR Emitter LED OP240A Ebay Farnell RS Components
Software
Arduino	Android
I have quite a few version of the various sketches so if you would like a particular version just request it in the comments and I sort out a link. Nokia 5110 shield sketch Nano with 7 segment display Chrono with 8x2 LCD	Here Aptoide store download