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.
> On 28 Apr 2017, at 3:04 AM, Wolfgang Jenne <wolfi(a)spider.li> wrote:
>
> One question: The OVMS v3 module: is it going to have some digital inputs somehow?
>
> thanks,
> Wolfgang
