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.

5V from 3V with Energizer

Some time ago I saw some Energizer emergency phone chargers for sale in a local cheap store, these were £1.99 each (usually £12.99, I think) anyway I bought several of them because the batteries that came with them would cost more than £2 for two. (not the ones shown in the picture)
Some time later it dawned on me that these were basically step up converters, 3V to 5V!

So I turned this

As it comes ..

Into this

Emergency charger with USB cable added

A portable 5V supply for anything with a USB power plug, I've also seen single AA emergency phone chargers and I suppose these will do just the same.

You can prise apart the body of the charger (there are clips inside that will release, with some teasing) and remove the 3.5mm socket from the circuit board inside the top silver part then the hole left was just the right size for the USB socket and lead I had lying around from another project or you could use a power tip for the other supply connecter for the Arduino.

Remove 3.5mm Socket (right) and add cable (left)

You could also remove the small circuit board and use it with another battery holder or even inside your final design.

Due to the higher mAH rating of the AA batteires I think they will last a lot longer than a PP3 9V battery.