This project started of as an idea of [Anna Dedova], who is a succesful rimfire pistol shooter. The initial question was whether a force sensor thin as tinfoil exists - a quick google answered affirmatively. So far we decided to use AVR (which I have some experience with), a flexible force sensor with the apropriate force range and the CC2540 BT 4.0 module from TI (well, the dx.com copy of it, we are high school students, not millionaires). We might as well add an IMU to monitor the caused movement. At best we will develop a script for logging the force (and delta movement) and displaying a graph, possibly an algorithm for finding peaks to cut the graph into small pieces for each pew and computing the deviation from the ideal linear function. Triggerwiggle, try saying that ten times really fast. Heh.
So the piece of scrap copper clad board I drew traces on didn't turn out good at all - when I started scrubbing it with the chloride, the traces smudged away! I relally didn't know that scrubbing it off makes it easier only for toner transfer made PCBs. Nevermind, grabbed myself a protoboard and soldered a few wires to the module I sticked to the border with some tape. Also I made a basic voltage regulator with three 10k resistors so the CC2540 does not get fried from the RX again. Heh. Fried T-Rex.
Yay for that! It's CC2540 based as well, but the unpopulated board pins are so tiny! I tried making an adapter board for it with the classic - laser printer, magazine paper, iron it on, peel off, dissolve excess copper. Since the spaces between individual pins are only 0,47 mm wide so that was quite unsuccesful - they sort of merged. Laser toner is just plastic you melt on the copper so no wonder. Order a good prototyping PCB? Not my thing. I have drawn the traces to pins we need (GND, VCC, TX, RX, RST) by hand with aan alcohol based pen. Aw yeah, old school. I shall etch and solder and be back with an update with pictures , hopefully we finally get to actually test it all with the arduino mini and the briliant code to build on from this series:
Thanks [WaiHoYan]! In the future I'm thinking once we have a proper working board to parse data to android, we could design a holder under the pistol barrel and 3d-print it in the nearest hackerspace brmlab.cz. Balance is vital. Give this a skull or follow for more updates!
I'm going to tell you a story of procrastination and bad timing. When [Anna Dedova] had the idea of building this device, I was on a German language course. Then I was with my family in Switzerland. Then for a week at my ouncle's house, doing DIY stuff, learning C and whatnot. Then is now - I had about four days to start writing stuff up and, being a procrastinator, am writing this just a few hours before the deadline. Also, the under 18 form is a bit stupid - you have to scan it again? It has the same legal potential as having people write down their names in an online form and would have the same probability of someone faking it. Supplyframe's lawyers kill trees. But the trees are slowly getting vengefull... just saying.
So according to the official rules, you must have at least four project logs. Huh. Okay: we have the sensor! I'm going to be having fun with it to test out how the area of finger affects the resistance and stuff. I order a Arduino Nano clone and an 9DOF IMU so in a few days we should be able to have some results!
In the beginning, we thought that sticking a USB cable in a notebook and having an Arduino on the other end would be enough. Well, nope! The cable would be freaking annoying when trying to get the ultimate shot. Bluetooth slipped into mind almost immediately as a pretty universal solution. BLE was chosen for the low energy consumption - we want to keep the weigh including the batteries low so the feel of the gun isn't heavily affected. After a while of googling a 0,25" force sensor was chosen due to the size of the trigger. The real challenge is mounting the sensor on the trigger, we might need to modify the trigger itself - or even opt out for a different solution. We'll see about that later, when we actually have the necessary supplies to get the thing going.