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.

Monitor Temperatures on your phone with an Arduino

After using the Bluetooth link to connect to the Chronograph I thought I'd use it to remotely monitor some temperatures, mainly because my fridge was acting up.

I connected the BT interface to the Arduino (my own version), this is quite easy because you just connect the TX from the Arduino to the RX of the BT interface and the sketch just uses the serial.print command.  This means you can test it out on your PC using the serial console in the Arduino IDE.

For testing I just make a small sketch to continuously output two random temperatures.

long randNumber;
long randNumber1;
long randNumber2;
long randNumber3;

void setup() {
Serial.begin(57600);
randomSeed(analogRead(0));
}

void loop() {
randNumber = random(5, 20);
randNumber1 = random(1, 10);
randNumber2 = random(5, 20);
randNumber3 = random(1, 10);
Serial.print(randNumber);
Serial.print(".");
Serial.print(randNumber1);
Serial.print("A");
Serial.print(randNumber2);
Serial.print(".");
Serial.print(randNumber3);
//Serial.print("A");
delay(10000);

}
The sketch outputs two decimal values delimited by the 'A' character, you can use any I suppose.

Within the App there is a settings screen where you can set Farenheit, enable the raw data to be seen on the main screen and edit the two temperature labels to something more meaningful.

I think I'll need to add the ability to alter the rate at which the app checks for data, currently it is 5 seconds, half of the 10 second rate from the arduino

My real world transmitter uses low power and only transmits once every minute and sleeps in-between.

If the transmitter used mains power and was permanently awake then I could request a reading when the app connects

App can be downloaded here or QR code  

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

Chronograph update

Latest project update for 2026 here

When I made the smaller screw on sensor that connected to the PC and fed the timing into a PC application, it got me thinking about different types of display that could be used and after a a good look around the net I came across a couple of options.

The first was a 7 segment LED display, these come in different shapes and sizes and could still be quite portable when added to the sensor.

The only problem with these displays is the amount of IO needed to drive them as each of the segments require driving. I then came across the Adafruit 7 display backpack, which takes all the hard work out of controlling the 7 segment displays.

The backpack details can be found here

The device is based on an Holtek HT16K33 chip that controls the LED segments and connects to the Arduino via the I2C bus and has a library that makes sending data to the display easy.

I bought one of the displays from Ebay and stuck it on the side of the sensor tube then added the code to the sketch to send the value for feet/second to the display after sending the uSecond value to the PC.

This would allow the chronograph to be used in conjunction with the PC via the USB lead or remotely with a battery pack, just reading the Feet/Second value.

Showing the feet/Second would require a lookup table to get the power from the velocity and the weight of the pellet, I suppose with a couple of small buttons added you could enter the pellet weight after power-up but before the first shot it could then alternate between the FPS and the power reading every 10 seconds?.

I then tried it out using my CP Sport Co2 pistol and it looks good.

I then used some of that PVC heatshrink, normally used for battery packs, it's really good as it shrinks using a hair drier and is quite hard when cool but can easily be removed with a pair of scissors or a knife.

Ideally I would have liked to use some clear but I only have red or white but surprisingly the LED shows through the PVC quite well.

Things to think about: -

• Writing the shot data to EEPROM for later retrieval
• Adding buttons to allow pellet weight to entered
• put together a battery pack for remote usage
• Think about power saving schemes
• Display battery power on power-up?
• Who knows?

Nano Sketch can be downloaded here you can use it with or without a PC, if you want the PC application let me know in the comments, it's still very BETA.

Fritzing file here.

More about the second option I found later.....

Chronograph - Part 6

Latest project update for 2026 here

Working on this project has really got me thinking and now I have my air rifle I needed to get something finished and usable ASAP before I started to tune the rifle, I don't want to go over the legal limit.

Whilst thinking about the total cost of the parts to make a usable chronograph, the one most people buy is £50, I had the idea of removing the LCD and just using the serial link to the PC.

So I thought about strapping an Arduino Nano to an aluminium tube with a 1/2" UNF thread so that it would fit on the standard silencer adapter, this would make it very stable.
I decided to use the Nano because there wouldn't be the need for a battery to power it, the USB lead would carry power and data back to the PC, people would also be able to programme them without having to buy the serial/USB interface.

Marking out the sensor distance

Tube screwed into the silencer adapter for my rifle

Fully assembled prototype with a foam spacer

Finished part attached to the Air Rifle

I used some thin but very tough heat shrink sleeving the same as that used to hold battery packs together on remote control cars

Below is a screen grab of the PC software (Ignore the FPS value, I'd forgot to change the calculation to 60mm spacing instead of 100mm)

Now for some more testing.