Copying OVMS developers in on this, as it is an
interesting question.
Free pins are very tight on the OVMS v3. We’ve added
so much as standard (extra flash, SD card, 3 CAN buses, etc,
etc) that there is not much free.
In the first draft design (shown on the attached
pictures), we had two general GPIO pins free - EXP_1 and EXP_2.
However, working with Espressif (the makers of the ESP-32 MCU)
it seems that the best and simplest way to use external flash is
to change the SPI bus chip select line and add an external flash
on that. If we do that, we need one more pin, and that means
goodbye EXP_2.
So, only one free GPIO pin - EXP_1.
We do have two internal expansion slots where
piggy-back boards can be plugged (one for the optional modem and
one free for general use). These use standard 0.1” SIP
connectors (two 1x10), so very easy to breadboard. For those, we
have EXP_1 on the attached diagram.
These pins are also available on a DA26 female
expansion connector on the side of the module (so you can use
them directly).
There is also a SW_12V switched 12volt supply on the
DA26 female expansion connector.
So, the short answer is if you just need a single
GPIO, that is available either internally of externally as
EXP_1. If you need a second, you could probably use the SW_12V
as well.
I/O expansion
If you need more than two, then you could use a
SPI bus I/O expander, probably on one of the internal
expansion slots, and use EXP_1 to drive that. The MAX7317 is
suitable.
In the first draft design for OVMS v3, we have
three relatively unused simple I/O pins
- MDM_EN - UART 2, modem enable (used to reset
the modem - very infrequent)
- SW_CTL - Switched 12V control signal (used to
turn on/off the external 12V - very infrequent)
- EXP_1 - expansion pin
What I’ve been considering is adding a MAX7317 as
standard, using EXP_1 to drive that (along with the normal SPI
bus used for two of the CAN buses), then moving MDM_EN and
SW_CTL to that. The MAX7317 has 10 I/O ports, so if we did
that, we’d get 8 free I/O ports from the MAX7317 as well as 2
direct off the ESP32 MCU.
I’m 99% decided to do that, but just trying to
work out cost impact and if there is enough room on the board
to actually fit it in.
Regards, Mark.
One question: The OVMS v3
module: is it going to have some digital inputs somehow?
thanks,
Wolfgang
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