The Idea for this project came from my building of a Spitfire500 accelerator .

The Spitfire500 is a 14MHz accelerator for the AMIGA 500 computer and has 8MB of fast ram on board , and an IDE interface . It is a good board , but lacks any indication that the IDE is working when accessing the on board IDE interface .

So , what can we do about this ? The best option is probably to use the Floppy drive access LED , so that it will show IDE or Floppy accesses .

On the schematic diagram for the AMIGA it uses Q503 ( 2N3906 PNP transistor ) to drive the floppy access LED . The signal comes through a 4K7 resistor to drive the base of the transistor , and light the LED . The most important thing is that this is an active-low signal , and on the IDE interface there is a pin marked /ACT . It is also an active-low signal , so I could use the same circuit as on the AMIGA to do the job .

A quick search on line showed that there was a surfscemount equivalent of the 2N3906 and that was the MMBT3906 in a SOT23 package . If I could make a pcb with two of these transistor’s and drive the base on the second one from the /ACT signal it could replace the Q503 on the AMIGA and drive the LED from either signal .

So order some MMBT3906’s and some small smd resistors ( 0603 ) size , lets keep the board as small as we can , so that it won’t be obtrusive and looks almost like it should be there . Ok I know what I am using so I designed the board while I was waiting for the parts to arrive .

It takes a long time to get things from china ( actualy it is about 10 days at the moment ) , but when you are anticipating there arrival it seems like months .

Finally arrived , and bodged a prototype . The floppy LED worked , but the IDE signal was holding it on all the time . Why ??? Then it struck me , I was using a compact flash to IDE adapter as a Hard drive , they run on 3.3v not 5v . the highest the signal could go was 3.3v and I was using 5v . I needed to lose 2v somewhere , an LED has 2v forward drop , and a friend had asked if i could put an LED on the board . There we go , an LED .

Here is the result .

Full details and build instructions on my website .

https://levosretrocomputerprojects.co.uk/a500-ide-flop