2N7000 + MCP23017 troubleshooting notes

Now I am using the RPi #1's MCP23017#1 keypad/lcd/stepping motor module to test RPi #2 and MCP23017#2.  I disconnected MCP23107#1 from RPi#1 and instead connected it to RPi#2.  I executed the LCD program and found that it worked OK.  This makes sure that RPi#2 and the I2C1 connecting wires are OK.

Then I tested LCD#2 and LCD#3 on MCP23017#1 and found them both OK.

This locates or confines that the problem is on the side of MCP23017#2 and the 2N7000 level shifting circuit.

Since MCP23017#2' Port A and Port B have been individually tested by hand OK, and also that the keypad program using PortA0~A3, and PortB0~B4 are OK.  This confirms that the 2N7000 leve shifter and MCP23017 conbination are working more or less OK, at least for individual LED and buttons, and also for the keypad.

Since I only have one set of 2N7000 3V3 to 5V0 level shifter and 5V based MCP23017, there is not other similar hardware to do swap testing, I think I would leave this 2N7000 + MCP23017 combination for a while and perhaps build another 3V3 based MCP23017 to do the testing.

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