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  • Author Author: phoenixcomm
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NexGen: Fuel Load Meter: Revised Plan of attack

phoenixcomm

imageFlash, Food For Thought:
Ok, I have a Smart Display, driven by an MCP23017 16-bit I2C which requires a lot of glue, (quick count) 8 data lines, 5 address lines, and 8 control lines. If you count this on your fingers 8+5=13+8=21. Ouch. Oh yes and the 5 wires for the switches. Remember that there is about 6 feet between the Display in the panel and the Arduino Mega, and I2C has a max length of about 12 inches, or about 5 feet short!
Now, what would happen If I could remote the MCP23017?? Then the only thing left would be the Switches and the Control lines.

The Solution:
I think I am going to use two (2) CPUs

  • An Arduino Leonardo will run just the display
  • An Arduino Mega will run, the switch interrupts, and CANaerospace Interface.

I can use RS-232 communication between the CPUs via a TI MAX3232 RS232 to TTL Module complete with a DB-9F connector on the module. I will have to write a simple protocol, that is what the message format is. In other words, I have to create the description and the field in the message. I have done this before so rinse and repeat.
My switch debounce circuits are all pulled up by a resistor with the rest of the debounce circuitry on the remote side.
Maxim has come to the rescue with a family CMOS Switch Debouncer they come in Single/Dual/Octal packages MAX6817 which has two devices in a SOT23-6 package, but even from Newark, there is almost $6.00 each. I guess I will go back to the Schmitt trigger, SN74LS14N HEX Schmitt trigger, and an R/C network. This solution costs about 86 cents for the IC + a few resistors and a cap. Since I intend to use  5 interrupts, I will keep them on the Mega. Below is a diagram of the system.

image

Wiring Plan
Arduino Mega IO Modules Arduino Leonardo Instrument Head
mnemonic pin mnemonic pin mnemonic pin mnemonic pin
SLC 2 SLC
SDA 3 SDA
INT INT
DP 13 RST1
DP 12 RST2
DP 11 CE1
DP 10 CE2
DP 9 CLK1
DP 8 CLK2
DP 7 RD1
DP 6 RD2
INT2 18 wire one-to-one FILL
INT3 19 wire one-to-one TEST
INT4 20 wire one-to-one UP
INT5 21 wire one-to-one DOWN
VCC VCC VCC
GND GND GND
RS232
TX1 18 RX 0
RX1 19 TX 1
VCC VCC
GND GND
RS232
TX TX
RX RX
VCC VCC
GND GND
CAN Module
CAN-SDA 20 SDA
CAN-SCL 21 SCL
INT3 INT
VCC VCC
GND GND

Notes:

  • I will be adding and or changing pin numbers as I go along.
  • 12/23/22 - Added the following: In other words, I have to create the field's descriptions and length in the message.
  • 12/30/22 - Major Change. Stupid Error: CAN Module uses SPI, not I2C please see: Revised Plan of attack-UPDATE
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