Complex Software Systems/Project Expansions Sound Expansion for the Acorn Electron

This is a small update to fix an error I found in the prototype build. I found during the assembly that I had made the footprint for the three larger capacitors too small and had to carefully solder small radial capacitors in their place.

I re-jigged the pcb layout to cater for the three larger SMD capacitors and ordered the new boards in black.

I looked out what components I had and ordered the few others I needed. The Bluetooth transmitter is a different version but is pin compatible.

Assembly starting..

Here is a comparision between the prototype and new board.

Time to program the three chips - simply copy the OS ROM and program the two PAL IC's from my previous jed files.

I found that my last 8K RAM was one recovered years ago and that the legs were tarnished and in two cases missing! I had no idea whether it was working but I was able to replace the missing legs.

The board is now ready to test.

Interestingly nothing worked! I say nothing, the bluetooth connection did work but the Expansion OS ROM and Sideways RAM didn't show up with the *ROM command.

I removed the two RAM chips to see if the Expansion OS ROM would show but it didn't so I then checked the ROM selection signals - all present and correct.

Then I remembered from years back that I had problems with some CMOS EPROMs not working correctly in Acorn computers and all my EPROMs are from that era. The EPROM I used was a National Semiconductor so I tried an Intel and finally an STmicroelectronics which worked perfectly. I reinstated the RAM to continue my testing.

I loaded VIEW and Advanced File Manager (AFM) into the battery backed RAM banks 2 & 3 which works ok then listened successfully to some music through the bluetooth speaker.

One of the items I had to order was the small speaker so I added that on.

and guess what? it didn't work! Checking all the signals and connections round the LM386 amplifier it should be sounding loud and clear but all I was getting was a very faint sound.

I removed the capacitor in series with the speaker which had a good solder connection and replaced it with radial version. That was it working.

Testing the capacitor it reads as 36uF (47uF) and it's impedance 6Mohms compared to the replacement, 50uF and 15Mohms. I don't really know what to conclude about this..

That's it debugged and working as expected.