Thursday, 28 March 2013

Chronnograph - Part 3

A bit slow going but I've got a bit further with the Chronograph, I had to enlarge the hole at one end by about 1 mm so it would fit over the end of the barrel (thanks Les), then I actually fired some pellets through it and so far it looks to be making reasonably sensible measurements, of course until I can compare it to another chronograph then I can't be completely certain of the accuracy.

As usual, I end up thinking of all the different ways I could achieve my goal .... and then have a go at most of them at the same time: -

  1. Remote transmitter attached to the rifle, using a receiver with a graphical LCD to display the results.
  2. Remote transmitter with a normal 16x2 LCD receiver.
  3. Remote transmitter with a Jeelink/Jeenode connected to a PC running an VB application to display the data.
  4. As no. 2 but with a smaller 8x2 LCD.
  5. As no. 4 but with  no transmitter and the whole thing mounted on the sensor tube.
I've had a dabble at most of the above with some good results, the Jeelink connected to the PC and using a VB application worked quite well.

Images below showing the received data from the Jeelink.  I also receive the transmitter's battery voltage level.

To determine the energy generated by the rifle/pellet you need to know the weight of the pellet in Grains, this can be adjusted to cater for the .177 pistol or the .22 rifle or different types of pellets.

Results from my 34 year old Diana air rifle

Results from my CPS CO2 air pistol with fresh Cartridge
I saw a discount offer on Hobytronics for their display range, this gave me an idea for the Arduino Nano I had laying around in a drawer, I bought an 8x2 LCD and connected it the Nano, a bit of a mess but it worked OK for a prototype.
Arduino Nano connected to an 8x2 LCD
This was linked to the sensors and also two buttons to allow for the pellet weight to be adjusted up or down prior to the first shot being taken.

This package was quite neat and small so I got to thinking about mounting the whole thing on the aluminium tube using a step up converter so I could run the Nano Mini Pro (Smaller) at 5V (16MHz) from one, or two 1.5V cells or a small lithium ion cell.

To do this as neatly as possible I decide to dust off the Eagle PCB layout tools and do a PCB, after all it's only around £10 for 10 off 5cm x5cm PCBs.

Rendered view of the PCB with LCD

Rendered view of the back of the PCB showing the Mini Pro and RFM12B

It's a bit of a squeeze but I got the LCD on one side the Arduino Mini Pro on the other and even got an RFM12B 868MHz transceiver on there, I couldn't help myself, I also added a couple of spare switches at the bottom of the display and a space for a temp. sensor (DS18B20) this will give me some alternative uses, remote temp monitoring/display etc.

There is also the 5V step-up converter on there, it's one of these.

More to come ....

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