System Modification Techniques

[channelmaniac]

Since I'm branching out into doing modifications for old game consoles and non-PC type computers, I thought it would be a good idea to start a thread about modding systems.

Enjoy!

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Subject: Adding LEDs to systems

It's a simple task to add LEDs to various game systems, both wall and battery powered. They use little power and if properly used generate little heat. However, they are a diode and will appear to be almost a short circuit and draw massive amounts of current when powered. This high amount of current can cause the LED to explode, get finger blistering hot, or simply burn out. To properly use the LED, a resistor must be added to limit the current. The size depends on the operating voltage and current of the LED as well as the voltage supply being used. A mathematical formula can be used to determine the size of the resistor needed.

The formula is:

R_ohm = (V_power-V_led) / I_led

In other words, if it's a 5v power source and the LED operates from 2.1v at 20ma then it would be: (5v - 2.1)/.020

Wait a minute! What's this .020? It's 20ma stated in amps. 20ma = .020 amps.

So subtract those voltages and you end up with 2.9/.020

Divide that out and you get R of 145 ohms. The closest standard value would be 150 ohms so use that instead. If the LED is too bright then simply increase the resistance which will lower the current draw.

Using this formula is an easy way to understand how to properly size the resistor to use for an LED in any application.

[channelmaniac]

Now that you've dreamed, designed, built, and tested your mod, how do you make it look professional? Also, how do you get it mass produced if you want to sell it?

Make your own PC boards!

Now, it's much easier than spending time drawing on boards or using photoetch techniques to design the board in some CAD software then ship it off to have it custom made.

First, download and install the EAGLE Light software from http://www.cadsoftusa.com/download.htm. It's a free program for hobby use, or cheap to register for business use. It's not something that will break the bank and will do Schematics, Layout, and Autorouting functions. It's $49 to purchase and will do board sizes up to 100 x 80mm, perfect for most game mods.

Second, read up on the tutorials on SparkFun:

Getting started with Eagle PCB and schematic capture
The basics of laying out a PCB with Eagle
How to create a custom footprint and part in Eagle PCB

Once the schematic is drawn and the board layout is made upload it to the PC Board manufacturer of your choice. I used http://www.batchpcb.com with good results. They charge $2.50 a square inch plus shipping and a per order processing fee of $10 (Check their website for current rates) In 2 to 4 weeks you'll have your PC boards back via FedEx.

Here's a picture of a 1" square board I designed for a composite video modification for the Colecovision game console. The assembled kit will be up for sale soon on my website.

[channelmaniac]

Removing NiCd batteries from systems and converting them to coin cells:

It's easy to remove a nickle-cadmium rechargeable battery from a board. The trick is to do it before it leaks and causes damage. But, what about getting rid of it altogether and using a simple non-rechargeable coin cell? This CAN be done but it requires looking at the schematic and neutering the charging circuit.

For Neo Geo boards this is very simple. Every model that uses the NiCd batteries are done the same way - by trickle charging the battery through a 470 ohm resistor that is located within an inch of the battery when the power is on. Removing this resistor neuters the charging circuit and allows for the installation of a coin cell battery and holder.

It's also simple on the Neo Geo boards in that the spacing for the solder holes is just right for fitting a coin cell battery holder to the board. For other games you may have to drill holes and fasten the battery holder either by drilling where there are good (and correct) solder points or by using some simple hot glue to fix it to the board and attach jumper wires to connect the battery into the circuit at the right point.

Be careful! If you connect the battery wrong you may end up with +5v connected straight to it. If this happens the battery could leak or explode spewing caustic lithium and other chemicals. These chemicals will burn skin and eat through traces so proper caution MUST be taken.

Enjoy!