The Jamsoft SI-1 is a recreation of the never-released AMSTRAD SI-1 for the ZX Spectrum +2A/B. It effectively turns a +2A/B into a +3.
It was designed using the excellent schamtics from Guesser and was a great first retro project for me.
Its designed to use a regular HD 3.5" PC Floppy drive and has a READY signal simulation built in. The READY signal simulation is implemented as several of the drive manufacturers metion - counts 2 INDEX signals after MOTOR ON. I also added a debounce of the INDEX pulses as my TEAC drive showed some bounching of the first few pulses, meaning it was only counting 1 rotation.
Never tried it with an AMSTRAD FD-1 and might not work even with a special cable due to the READY signal simulation. Would probably work with a Gotek but not tried.
I've also implemented a switch to change sides of the disk or support the uPD765 head
It doesn't feature a power supply for the floppy drive as I was very worried about overloading the +2A Power Supply as I'd read that the +3 had a beefed up supply to deal handle the floppy drive, but I think I was probably being over-cautios and it would work fine with a 'modern' (90s-00s) 3.5" PC Floppy drive.
This was my first ever PCB design and as such there are some howlers in it that I haven't had time to correct, issues are:
- Missing decoupling capacitors for the READY signal simulation logic ICs
- Decoupling capacitors that are there are not next to the ICs and just randomly scattered across the board
- It's a milimeter or too too wide and getting a bit in the way of the PSU socket. I can just get it to fit with a bit of wiggling.
- VCC traces are same width as signals... However saying all that, I haven't had any issues with it up till now...
This has worked for me for most games I try, but I've had problems with one or two (ie, Double Bubble didn't work for me):
- Load the .tap/.tzx file in an emulator (like, FUSE) set to +3 mode
- Pause the eumulator once loading is complete and save a z80 snapshot
- Repeat 1-2 for another 4-5 games (I can get about 5 games on 1 side of a disk)
- Use the amazing Z80onDSK from Tom Dalby to create a .dsk image of the snapshot files, using a command like:
z80ondsk -l thewitch.z80 -o witch snowed128.z80 -o snowed mikie.z80 -o mikie Feud.z80 -o feud games1.dsk
- Use HxCFloppyEmulator to convert to .dsk to .hfe disk image
- Use Greaseweazle to write to a floppy disk. If using a HD disk, make sure to cover the HD hold to make it a DD one. Also tell Greaseweazle to only write to first side (head 0), using a command like this:
gw write --tracks="c=0-81:h=0" games1_dsk_d.hfe
- Pop disk into the speccy and hit loader, select the game you want to play from the menu and enjoy!