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A project log for MCM/70 Reproduction

I am making a full sized MCM/70 reproduction, a Canadian personal computer from 1974.

Michael GardiMichael Gardi 12/02/2022 at 15:130 Comments

As with my Sol-20 project, the keyboard encoder is expecting 5V while the Raspberry Pi 4 operates at 3.3V.  So to overcome this I purchase a Voltage-Level Shifter Module from Amazon. Here is what it looks like.

I am using the Sol-20 header on the encoder and the pinout looks like this.

So here is how I wired the keyboard. Note that for the exception of +5V and GND lines which are wired to the 3.3V side or the level shifter, all of the other connections are wired to the 5V side.

Keyboard EncoderRaspberry PiDescription
+5V5VPower
GNDGNDGround
D0GPIO5Key 0 bit (low)
D1GPIO6Key 1 bit
D2GPIO12Key 2 bit
D3GPIO13Key 3 bit
D4GPIO19Key 4 bit
D5GPIO16Key 5 bit
D6GPIO26Key 6 bit
D7GPIO20Key 7 bit (high)
STROBEGPIO4Key ready on falling edge.


The display has the following pinouts.

All of the following connections are wired to the 3.3V of the level shifter.

Display ModuleRaspberry PiDescription
3.3V3.3VPower
GNDGNDGround
dataGPIO21Data Pin
selectGPIO22Register Select  Pin
clockGPIO23Clock Pin
enableGPIO24Chip Enable Pin
resetGPIO25Reset Pin


Next step, mount everything into the case.

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