NexGen: Hacking the Fuel Load Indicator III - Hardware Design

26 Aug 2018

I have talked about the Fuel load Indicator twice before, first here and then here. So here is the hardware design and its analysis.

Analysis: In my last blog I noted that between the display and the switches I am using about 25 pins + ground and power. So to recap here are the pins: I have added a second table which shows the I/O connections. The reason that I chose the STM32 was for its size. It can easily fit inside the enclosure (approximately 7cm square).

The Plan:

The Hardware: Since the original back will be of no use to me I will have to print a new one. I will have two connectors on the rear. 1) a DB-7 for my CANbus Data and 2) a DIN 5 for my 5 volts. I will have to use UTA, the University of Texas at Arlington, Maker Space Laser Cutter to cut my vector board (FR4 PCB) to shape. In this way, I can put my connect the STM32xx and the two (2) TI PCF8574 I/O expanders.

The Software Overview: The software design is rather simple as the STM32 is just being used as a dumb terminal but without the keyboard This will only need 4 keys And instead of a UART and RS-232RS-232 I will be using a CANbus transceiver

Display Info
Mnemonic	J1 pins	IO Exp	STM32
D6	1	IC1-11
D4	2	IC1-9
GND display	3
GND logic	4
D0	5	IC1-4
D5	6	IC1-10
D3	7	IC1-7
D1	8	IC1-5
A1	9	IC2-5
D2	10	IC1-6
A0	11	IC2-4
A2	12	IC2-6
FL - Not Used	13
CLS.1	14		10
CLS.2	15		11
WR	16		12
CE.2	17		13
RD.2 - Not Used	18
RD.1 - Not Used	19
CE.1	20		14
D7.2	22
CLK.2	21		15
CLK.1	23		16
D7.1	24	IC1-12
RST.1	25		17
RST.2	26		29
A3 & A4	27	IC2-9
Vcc	28
A3 & A4	29	IC2-7
Vcc	30