First take bog-standard used PCs, no longer wanted by westerners and adapt it for rough terrain and rough environmental conditions.
Remove all drives-they just won't survive. No floppy drive, no hard drive, no optical drive. Sand, dust, heat, moisture, and bugs will do for them. Now develop a simple solid state replacement for the floppy drive that looks to the system like a floppy drive, and works like a floppy drive, but isn't. Burn your entire bootable OS and a multi-purpose works package on to this in a ROM, with space for data and eeprom for new software (replaceable cartridges would work well here). Now glue all the internal connectors and cards into place. Remove the prcoessor fan and any other fans internal to the unit, and seal it up so it is water, bug, and dust proof. Make sure your software automatically reduces the processor speed to keep the CPU temperature down. Then measure the power consumption of the unit. Replace the bog-standard PSU with a lowest-power-requirement PSU, with no fan but a very large heatsink. Add a trickle-recharge storage cell-based UPS to cut in whenever the power flickers. Your new PSU needs to cope with any supply voltage/plug. I/O ports need to be isolated from the internal circuitry so solder on facing adaptors. Use clear symbols to indicate which device goes where. Multi-standard TV output is a good additional option for the developing world. Include basic networking/syncing, with the option of a TCP/IP stack and e-mail software, customised for noisy lines.
Alternatively, a much lower power device can be custom-constructed, and mass-produced to get the cost down. Either use an 8-bit CPU or a microcontroller, solid-state memory chips, and OS/software on ROM and EEPROM in a cartridge. SRAM for data. 4-line LCD screen on the unit, with external multi-standard TV/monitor output. Water/dust/bug-proof with a touch-sensitive keyboard on the front of the unit, though with a port for an external keyboard and mouse. Serial/parallel, possibly USB for (isolated) I/O. Sound I/O. Battery powered with trickle recharge from the mains. The internal battery would act as a UPS on a dodgy mains supply. Clockwork, solar, and dynamo recharging would all be options. Include basic networking/syncing, with the option of a TCP/IP stack and e-mail software, customised for noisy lines.
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