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.

Chronograph - Part 4

Latest project update for 2026 here

The PCBs arrived, at last!

They look good and after assembling the parts, the design works, well I've not tested the 868MHz transceiver yet but the LCD display connected to the Arduino Mini Pro clone works fine and when connected to the sensor fitted to the gun all seems to be OK.

I used a scope to check the calibration of the value sent from the Arduino and it looks pretty good.

Front View - LCD and switches

Back View - the Mini Pro plugged in

Various part plugged in

The PCB is essentially a carrier board for the processor and the display and the 5V step-up converter.

Using an oscilloscope I fired some pellets with my pistol through the sensor tube and compared the timing reported by the Arduino, via serial to the PC, with the measurements taken with the scope.

Scope display showing time between pulses

As you will see from the picture the timings are not exactly the same but this could be due to rounding or the fact that the Arduino only has a 4uS resolution for the micros() function.  I will do some calculations to see what the effect on the final FPS or FPE values would be.

Air rifle chronograph

Latest project update for 2026 here

For some time now I've had an old Diana air rifle in the garage gathering dust and it's been a long time since I used it but I recently got interested again and even bought myself an air pistol.

As usual I like to have a tinker with anything I can, including my air guns.

One important tool you need when tinkering with airguns is a chronograph, this lets you check the power of the gun to make sure you don't go over the legal limit allowed for the maximum energy.

To buy a small clip on chronograph was going to cost me £49..... "hang on" I thought, I've got all the parts I need to make my own chronograph using the Jeenode.

So, the basic idea is to put two IR beams about 100mm apart in a tube and use the jeenode to time the duration between the first and second beams being broken by the pellet.

If you know the weight of the pellet, the speed and distance travelled then you can calculate the energy used to fire the pellet.

Some googling had come across a few projects form other people and given me a few good tips and even some basic code to start with.

Where my chronograph would be different was that I was going to use the RFM12B to transmit the timing information to a remote receiving station using my "alternate jeenode" and displaying the information on the GLCD.

I chose IR sensors that had a buffered logic output, this would give a clean square trigger signal.  They're also quite fast at 25nS rise/fall times.

OPTEK TECHNOLOGY - OPL550A - PHOTO SENSOR

I Chose the matching IR LED to go with the sensor, OPTEK TECHNOLOGY - OP240A. - IR EMITTING DIODE

So, I started the prototyping whilst waiting for the IR sensors to arrive, to test the code I used a couple of switches to simulate the trigger sensors.

And used an oscilloscope to get an idea of what the real timing was and sorted out the code until it matched the oscilloscope measurements.

Cursors placed on the leading edges on channels A (trigger 1) and B (trigger 2)

When the sensors arrived I used some plastic waste tube I found in the garage to mock up the triggers at 4 inches apart.

I tried out the sensors by dropping some objects down the tube and reading the results via the serial link to my PC, all seemed well and the times were in the ball park when compared to some calculations I'd done earlier.

..... Next steps, write the receiver code for a 4x20 LCD and also the GLCD and maybe look at a VB programme to receive the data on a PC and display the results.

Multi purpose ATtiny84 PCB

Thanks to stumbling across a couple of ATtiny84 blogs here nathan.chantrell.net and here http://harizanov.com  I was inspired to create my own PCBs for an ATtiny84 chip.

The biggest inspiration was the link to an extremely cheap site for the production of PCBs, in fact 10 off 5cm x 5cm only cost $13 inc. postage.  Ten PCBs for a tenner, Fantastic. Link

I used the Eagle files from Nathans site and modified them to suit my requirements by adding the connections for an SD card, a CR2032 battery holder, 2 extra DS18B20 probes and an LDR, both the DS1820s and LDR have switched power supply using an output pin. (idea from Martin's corner of the web)

The finished PCBs arrived today and they look pretty good.

I'll build one up later next week and get programming.

My next PCB is an add on board for my USBtiny ISP programmer so I can program a 328P, ATtiny84 or ATtiny85.

If anyone wants the eagle files for the PCB below then just let me know in the comments.

Schematic

PCB

OOPS! noticed that the labels for the VCC, VCC1 and GND, GND1 are swapped over, the top pair are actually VCC and the lower pair are actually Grounds

3D rendering in Google Sketch up

Actual finished PCBs

Here is a link to the files.

Really Really small Oscilloscope

I came across this post on the Jeelabs website and thought it was worth posting.

Dual Channel Oscilloscope and waveform generator

This thing is about the size of a 9V PP3 battery, based on an ATXMEGA32A4 processor with a 0.96" white OLED display it includes the functionality of a dual channel oscilloscope, multimeter, protocol sniffer and waveform generator.

It can be found here and there are some videos of it in operation here.

Multimeter mode

The firmware can be updated but it needs a special USB/programming cable and it will, in the future, be connectable to the PC and use PC based interface.

The waveform generator operates independently from the scope function so you can apply the signal to a filter circuit and watch the results on the scope.

It's also possible to write your own software and use it for other projects, there is one picture on the site showing it displaying temperature from a DS18B20.  I think this requires a special programmer though.

All for a price of $49, a bargain!

I don't know about availability in the UK but If anyone sees it for sale in the UK please make a comment.