A connector that fits into the parallel port on the back of your computer
220 ohm resistor
4 or even 2 might be sufficient, but eight provide more power
electrolytic capacitor >= 47uF 25v
Might work fine even without it, it just smooths the supplied power
28 pin IC socket,
small width (7.54mm)
I usually prefer precision sockets, but of course it works fine with the cheap ones too
ATmega8-16, DIP version
The actual chip
Not essential, but generally recommended for ICs
(Optional) status LED
Building the programmer
We will now build a programmer called SP12. The advantage of this programmer is that you don't need any external power supply because it's powered by the parallel port.
This is the schematic of the programmer
X is the D-SUB 25 connector; X-5 for example means pin 5 of the connector
ICS1 is one of the IC sockets - mind the notch!
R1-R7 are the 220 ohm resistors
C1 is the electrolytic capacitor; mind the polarity - there will probably be one side marked with a "-", this side must connect to the GND line on pin 25 or the D-SUB 25 connector
For your help, this is the pin numbering of the D-SUB 25 connector, looking at the backside where you have to solder to.
I built my programmer right into a standard D-SUB 25 case. This step is mainly to improve the appearance of the programmer, and is a bit fiddly too, but if you want to do the same this is how I did it:
I used a Dremel to cut two large parallel holes into the case, 7.54 mm apart
I placed the IC socket on the case so the pins go through the holes. Then I fixed the IC socket with some glue
I cut off all pins I didn't need
I soldered all wires to the correct pin; this is the programmer right before I closed the case
And this is how it looks like once the case is closed
Building the chip
(This part is just about adding the optional status LED and a capacitor to the modchip. It's no essential step, so if you want to know if the programmer you just built works, you can do the next chapter first)
Now we're going to build the actual modchip. The chip will work without any other components, but you may want to have a status LED for just a few cents more. And even if it seems to work fine without it, you're generally told to add a 100nF capacitor between VCC and GND. And this is what we'll do now.
IC1 is the ATmega8 - mind the notch!
LED is the status LED (mind the polarity - the long leg of the LED is the one you need to solder to pin 26)
R8 is the series resistor for the LED
C2 is the 100nF capacitor
I soldered all parts directly to the IC, this is what I did:
I put the chip in the remaining IC socket because you can only solder to the upper part of the pins, otherwise the chip will not fit into the socket anymore
I soldered the 100nF capacitor directly to the VCC and GND lines. BE CAREFUL IF YOU DO THIS - If you don't do the soldering fast, the heat might kill the chip!
I soldered the LED to pin 26 and connected it to the GND pin through a series resistor. Again, BE CAREFUL, you could easily overheat the chip.