There are some developments with this project since the last log. With these, the RAM Disk for the PX-4 is more or less complete. The base board works, there is a compact battery solution and a case. 

For the PX-8 a new board will be produced. The existing board works OK, but when installed with the case, it blocks some other useful ports. The new board will be less wide.

Backup battery

The backup battery is based on a CR2032 3V Lithium cell. It uses a custom board and a clip purchased in China. It is very compact, cheap and easy to assemble.

backupBatteryClipParts.jpg:

Extension board

The Extension board is assembled and the plan is to fill it with data mimicking an 1 M Byte ROM, which should be recognized as drive K: on the PX-4. The other memory ranges are not supported by the Operating System, but can be used as extra non-volatile memory. One option is to keep backups for the active RAM Disk. 

px-4RAMDiskExtensionBoard.jpg:

Board correction

When designing the new PX-8 board, it was found /OE line is not connected. That is what you get if you use more than one name for the same signal. The wire is from J2-26 to U11-24 (the /OE pin).

px-4RD_OEbodgeWire.jpg:

Show case

The current case is large enough to contain the base RAM Disk board, Extension board and backup battery. For just the base board a lower case could be designed, but this is left to the user :-).

PX-4RAMdiskShowCase.jpg:

New board for the PX-8

The planned new PX-8 board uses the same circuit ast the original, but the PX-4 connector is omitted. Instead the PX-8 connector is moved to the edge, allowing it to be used next to the PX-8 case, without the need for a cable. Designing a case like the original wedge is possible, but more complicated.