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Wecome To The New Home Of TheEPROM9
Photos Of The Guts
Photos Of The Guts
These RAM packs once again use the Humble HD61914 4-BIT 1KB RAM chips. Hence there are two of them on the board. The passive components are for the battery support hardware that keeps the RAM alive when disconnected by the machine. The RAM packs can hold the data for about two years when external the the computer. When internally mounted that time is longer. The capacitor on the board holds the power long enough to allow for changing the battery without losing your data or programs.
The schematic is an interesting one with this one due to the battery circuit. It is surprisingly simple just consisting of some diodes & resistors. I have yet to determine the diode type. I'll hook it up to a curve tracer to determine it for good, the part number H.M does not really give anything away.
Other than that the schematic is not all that different from the other RAM cards that use the HD61914 chips.
My projects notebook was very handy for noting down dimensions, pin outs & the board layout. Always have a notebook like this. It is a lot easier to be able to draw stuff in it than on the computer.
When it comes to designing the PCB, always be willing to print off a copy of the PCB in a one to one mode so you can test the dimensions against the real PCB. Saves sending it off only for the dimensions of holes & whatnot to be wrong.
Bottom of the PCB.
Top of the PCB.
Top of the populated PCB. With PCB art & connector to the compute.
Bottom of the populated PCB with all the operational components.
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