13 February 2010

BloodBowl Turn Counter Using 7-segment LEDs

BloodBowl Turn Counter Using 7-segment LEDs:

BloodBowl Turn Counter Using 7-segment LEDs
This project was for a BloodBowl game turn counter using six Charlieplexed 7-segment LEDs.


A friend of mine asked me about ideas for building Bloodbowl Turn counter for his boardgame. Not knowing what this was, and what he wanted, it took awhile to decide on if and how I was going to do this.

I first had to have an idea of what he wanted, so I started with concept art (picture). The basic idea is to have 3 push buttons, controlling 3 LED's each and it would be placed inside a custom built tower.

The only big request was to have the top 4 displays count up from 0 to 8 and reset, and have the lower 2 displays count down from 8 to 0 and cycle back.

I would complete the circuit, and he would complete the tower.

Design & Parts List:

Design & Parts List
Since the concept called for 6 7-segment LED's, and I had some 8-bit Microchip PICs handy, I researched ways of using the PICs to control LEDs.

" Up to 6 displays can be accessed like this without the brightness of each display being affected." I considered this a challenge and something to investigate as part of my project.

The First thing I did, was grab some incandescent 7-segment displays from my box and see how they would work. Bad news. The particular parts I selected were not behaving like I wanted. The segment would light when needed, on the breadboard, but leakage current was distributed to the other 6 segments. I realized incandescent displays may not be the way to go, or I needed to use them in a different way. So for simplicity I verified the 7-segment LEDs I had on hand would work for breadboarding, and ordered some common anode displays.

The Second thing I needed to do was layout my design and start work on the code. Pictured is my circuit. Not much to it, as the code in the PIC takes care of the multiplexing...errr Charlieplexing. Note: ALL 6 displays have the SAME lines from the driver IC. The selector IC enables each display, 1 at a time, and the 7-segment lines are updated by the PIC accordingly. Very simple idea.

After that, code and hardware completion is all that was needed.

Parts List
After 3 small orders from Digi-Key while deciding on specific components, I had everything I needed (with some stuff on hand);
1 ~3"x4" PCB
6 small push button switches (N.O.)
1 74LS47 , 7-segment display IC
1 PIC16F627
1 CD4028 , 1 of 10 selector IC
6 10KOhm resistors
1 470Ohm resistor
1 spool of wire. I used various colors and guages, but that was just me.
1 78L05 5V regulator
1 9V battery clip
1 9V battery
1 small switch (for power on/off)

I consider this a moderately complex project, due to;
1) Microprocessor code required
2) Soldering and breadboarding
3) Design optimization.

None of these issues by themselves are overly complicated, but taking them all on without any experience can be abit much for the beginner. A hardware programmer is required to burn the device, soldering station, etc...

The FIRST thng someone might notice is that the 7-segment LED's DO NOT have series (current limiting) resistors! Let me address that quickly, by stating my original design had them in...but read the next step for explanation!

PCB Soldering:

Everytime I get to this point in my project I delay abit. At first I was going to wire wrap this thing, but quickly dropped that idea.

At first I think "A few wires to solder, no big deal"...then, by the time my project is ready to be soldered I am thinking, " I should have either sent out to have a proto board made, or etched my own board".

I am not into PCB etching (yet), and didn't want to pay $$ to have a board made, so....

Yeah.....I spent about 3 hrs soldering this thing. It's about 150 wires, so that's 300 solder points, plus touch-ups for solder bridges.

Anyway, here's the back side of the board pictured....yeah...abit of a mess, but when it was all done I only had 1 solder short. Took 20 mins of thinking since the display showed the wrong #'s being displayed in a logical pattern that I had to decipher. After that, I located the short, and bam! It worked perfectly.
PCB Soldering



This project took about;
~2 weeks to think about and email fine points to requestor,
~3 hrs of code completion and debug,
~4 hrs of breadboarding and debug,
~3 hrs of soldering

Using just 3 IC's it is possible to Charlieplex 6 7-segment LEDs.
Power draw is at about 30mA with this design, which isn't bad if I do say so myself.

I suspect more 7-segment LED's could be used, but have not pushed the envelope.

This idea could be applied to almost ANY application using 7-segment LEDs; thermometer, clock, text display, etc. With some tricky code, you could have a moving display, or pictures...maybe even a base for a POV (persistence of vision) project.

The final implementation is left for my friend to build his Tower and place the board in, as he see's fit. If/When that is done, I will get a picture uploaded. But as for the circuit, this appears to be built to order!
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