Chronograph completed - Finally

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: -



Approx. cost

3D printed enclosure - Thingiverse
£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

RS Components

RS= £2.25, 5 off
IR Detector x 2 Ebay
RS components
RS=£5, 5 off
Arduino SketchHere 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.


Csokáv said…
Hey, now I can comment. Cool. I'm copying my comment from thingiverse, it's not about the 3d printed part.

The reading of the sensor is an analogue-digital conversion and that takes a lot of time and the time the pellet passes one sensor is very short. The polling of the sensor must be happening when the pellet is in front of it to be registered.
I don't know how an interrupt works on these sensors, but I assume that also includes an AD conversion, or not? Or the interrupt happens on an analogue signal change? I have no idea really.
Gadjet said…
Glad to get your comment.
I didn't use standard IR detectors because of the overhead, I used detectors with a digital output and a response time measured in nS, the detectors feed into D2 and 3 which are both interrupt enabled. when the beam is broken the detector pull down the input to ground.

The original sketch just sat in a loop checking the first detector and then started counting uSeconds until the second detector is triggered. In the latest version I've used the interrupt function so that I can do some other stuff in the main loop.
Csokáv said…
Great, I didn't know detectors like that exist. Thanks.
Gadjet said…
No problem, Follow the link in the post :-)

Stuart Smith said…
Would you be willing to make one for sale as I have no aptitude to understand a lot of this blog,but your ability amazes me. Would love one with its own battery.
Gadjet said…
I don't really have the time to go into production with these, it's aimed more at a DIY project, having said that I've agreed to build a batch of 5 for some guys on an airgun forum.

Would you be interested in a kit of parts to assemble? just a bit of soldering?

The other problem with selling them is they are not production quality I consider them to be prototypes and as such I could not offer the guarantees that most people would expect when buying things.

Unknown said…
Where can I find arduino code and schematics for this project? Thanx
Gadjet said…
There is a link in the post to the sketch and the schematic is in another post somewhere, search for chronograph.
Gadjet said…
I've updated the post with a representative Circuit of the Chrono, the only thin missing is the charging lead and power switch but this should be obvious, if not let me know
Rich McManners said…
I'm going to be having a go with a NodeMCU... bluetooth and wifi on board for less than a fiver, I'll let you know how I get one. :)
Anonymous said…
Chrono_with_interrupts.ino also missing from dropbox
Unknown said…
Hey, the Arduino Sketch dropbox link is still dead.
Gadjet said…
Sorry, I will fix it but I have a problem accessing my blog, I changed the template a while ago and now I don't get the "sign in" option
Gadjet said…
Links now fixed .... I hope
Unknown said…
Well, the link isn't dead now, but it's the very barebones Serial communication version. I was curious about the interrupt version, and the bluetooth code so I could use it with your Android App.
Gadjet said…
Ah OK! I can add a link to the interrupt based version but when I did the accuracy testing with an oscilloscope

I actually found that the interrupt driven version was less accurate ..... Go Figure!

I don't know why, do you still want it it's here

As for Bluetooth, there's no Bluetooth code, the BT interface just takes in the serial data and sends it via BT to the phone, the sketch you have will already work with the BT module and Android app.
henkie tenkie said…

I am now making something like this, but wondering... What would be the maximum nozzle speed, using a 6 cm space between the two sensors? I mean, will it work with an airgun (not airsoft)?
henkie tenkie said…
Hi again! Another question; in your wire diagram you use resistors. What is the value of the two resistors?
Gadjet said…
I've never tried them at any distance apart greater than 15mm, the problem is being able to ensure that the pellet obscures enough IR light from the emitter to trigger a detection.

It may work OK if your detector is down at the bottom of a hole so it's directional in the IR it receives and ignores the scattered IR from around the pellet.

The usual method to detect pellets over a distance is to use several IR diodes in series/parallel (Analogue) to detect the shadow of a pellet passing over them like the Chrony F1 etc.

Sorry, I should have added the value, the resistors have the colour code brown, grey, brown = 180 ohms :-)

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