So i ride motocross and it sucks balls timing your buddy and writing his times on a pit board for him to see so thats where this idea came from. Automation and electronics is your friend:)
So the First thing was to build a big ass Seven Segment Display. i used 5mm LED's and 360 of them haha. the Display is about 10 inches high by about 32 inches wide. It has 4 digits and decimals as well. The next thing was to drive the Display. What a learning curve.
I am using an atmega328 to do all the thinking. And obviously there are not enough pins to control all 31 segments so what did i do? At first i panicked and though i wasted my money buying the arduino uno R3 but i did research and came across multiplexing:) it Took me a very long time to understand what multiplexing is cause this is my first electronics project ever!!!!!!!!!!!!!! i started about 2 months ago reading on electronics and read up on the raspberry pi and i was like wow thats kewl. I have a background in programming as i got into it a few years ago but i learnt python and basically just wrote useless command line programs and one nice GUI, like a data base for names numbers bla bla. Anyways so i researched further on this Raspberry pi because i thought "Hey now i can actually do something useful with my programming knowledge like interact with lights and switches and the real world!!!" so i carried on reading and came across the arduino and microcontrollers and then i was like that one!!!!!!!!!!! So i bought the arduino uno R3 and started learning C programing.
Sorry im talking so much im just giving a whole background to my project. Ok but thats enough. back to the LAp timer.
So i figured out that multiplexing is basically just switching between the displays very fast and your feeble human brain is fooled and it thinks all the digits are on at the same time. So this was like so interesting for me, i could not believe how clever this was, it is unbelievably clever!!!!!! So i was like i AM DOING MULTIPLEXING AND THATS THAT!!!!!!!!!!!! i bought shift registers and a whole bunch of stuff and read up on that but i still wanted to do the multiplexing because i wanted to learn about it.
So the display i built is wired up as a Common Anode and i switch between grounds to multiplex the different digits.
The next brick wall i hit was that the microcontroller can only put out so much current and i panicked again!!!!!!!!!!!1 but then i hit google and discovered the world of transistors and mosfets!!!!!!!!! YAY!
So then i found out that i need to do high side switching and i need to use n channel mosfets or npn transistors to drive p channel mosfets or pnp transistors!!!!!!!! i was like HUH!!!!!!????????
I asked for help on this forum and many people helped me understand this concept so thanx alot to everyone that helped me.
So the way the timer works is i have a laser shining on a photodiode which is connected to the analog pin and ground. When a bike comes past the analog value drops and the program triggers the timing mechanism and displays a lap time. Its hard to explain but i will post the code i wrote.
Here are some pictures of my project
The Display frame
The Control Box with all the electronics
High side switching
Low side switching
Stand alone atmega328
Display with LED's in displaying 15 seconds
viewing display headon (the LED's have a 20 degree viewing angel and are very bright if you within the angle. The photo is a complete blur but the human eye can read it perfectly. very bright.
I still need to sort the laser out as it gets hot and dims after about a minute or so but i have a heat sink and will be fitting it shortly. Anyways ya this post might be a mess but thanx to all the people that helped me out especially MR CrossRoads
So let me know what you guys think:)