Posted about it on the INDI forum and had a reply from the author of INDI   Just asking for details - I've replied.

As a bit of an aside I'm wondering about possibly combining my ASC with my weather station wind instruments - putting both on the same mast.  Problem might be the windage of the ASC. 

Back to INDI drivers :-  I've sorted out why the labels on the buttons were wrong   Also, if more than 4 switches are set up the control transforms into a drop down list.  I've been thinking about the whole control system too.  I think the Astroberry Focuser is overkill for this application - I don't really need auto-focus and I've found it's usually ineffective for such a wide FOV anyway (it works fine with standard lenses and telescopes).  Also, I can take better control of the limits if I control the motors rather than using the standard INDI focuser.

Here's an image with the camera just pointed out of the window - it shows that with gain at zero and exposure at the minimum of 32µs the ASC will work in daytime   (I know it's out of focus.)

Regarding focussing, I think buttons for coarse and fine, in and out would suffice.  So 4 buttons - Coarse IN - Fine IN - Fine OUT - Coarse OUT.  Each click of the button moves the focus by a certain amount (to be determined by trial).  Then, the 4 motor enable buttons - ALL - A - B - C.  I could also have an overall control of ON/OFF - a "safety catch".

Here's the way it looks - still have function to add.  Actually, there's still a lot there that I don't want

A bit less clutter

Moved the focus motor controls to the Options tab.

Think I would prefer the buttons in a different order. ie.  CLOSE, OPEN - OFF, ON and IN Coarse, IN Fine, OUT Fine, OUT Coarse.  That's easy

Here are the GPIO pin assignments :-

#define IN1 RPI_BPLUS_GPIO_J8_29	// GPIOO5  Lens Cover
#define IN2 RPI_BPLUS_GPIO_J8_31	// GPIO06  Dew Heater
#define IN3 RPI_BPLUS_GPIO_J8_33	// GPIO13  Camera Cooler

#define M0 RPI_BPLUS_GPIO_J8_15		// GPIO22  Motor A
#define M1 RPI_BPLUS_GPIO_J8_13		// GPIO27  Motor B
#define M2 RPI_BPLUS_GPIO_J8_37    	// GPIO26  Motor C

#define DIR RPI_BPLUS_GPIO_J8_07	// GPIO4
#define STEP RPI_BPLUS_GPIO_J8_11	// GPIO17
#define SLEEP RPI_BPLUS_GPIO_J8_16	// GPIO23

From trying to get focus manually by turning the gears, it seems one tooth of the 12 tooth gear makes quite a significant change in focus - in fact from way out one side of focus to way out the other side.  So 30° rotation of the motor shaft is actually quite coarse and I could allocate this as the size of the coarse step.  The stride angle of the motor is 5.625°/64 approx (64:1 is the approximate gearbox ratio).  So 30° corresponds to 30x64/5.625 = 341.3r steps.  So we could make coarse movements say 400 steps and fine movements 40 steps as a first try.

The basic code for controlling the motors is :-

    for ( int i = 0; i < ticks; i++ )
    {
        // step on
        bcm2835_gpio_write(STEP, HIGH);
        // wait
        bcm2835_delay(STEP_DELAY/2);
        // step off
        bcm2835_gpio_write(STEP, LOW);
        // wait 
        bcm2835_delay(STEP_DELAY/2);

        // INWARD - count down
        if ( bcm2835_gpio_lev(DIR) == HIGH )
            FocusAbsPosN[0].value -= 1;

        // OUTWARD - count up
        if ( bcm2835_gpio_lev(DIR) == LOW )
            FocusAbsPosN[0].value += 1;
    }

This counts steps but to make the numbers smaller and more suitable for a meaningful display it would be better to work in units of 40 steps per tick and using an inner loop with a count of 40.

With the clear nights we're getting currently I feel the need to get on with the hardware then I can make a first stab at the software to get something working and tidy up later.

I shall be controlling all the motors directly from the RPi and not use the Arduino Nano.  That's the three focus motors and the lens cover.  So all 5v versions of the 28BYJ-48 modified for bipolar connection and A4988 driver modules.  The diagram below show a basic circuit for the A4988 module but I shall be using ENABLE, SLEEP, STEP and DIR with the RESET and VDD connected to the +3.3v rail.

This diagram shows the connections for the three focus motor drivers.

ATM I have just one GPIO pin allocated to the lens cover but I'm now planning to use a stepper motor driver connected directly to the RPi so will need more.  I don't see this as being a problem.  I could piggy back the lens cover motor onto the focus motors but I'm not sure I want to do that, I'd rather keep them separate.  I need at least one pin with pull-up for the Hall switch.  Then three pins for DIR, STEP and SLEEP.  Best to have pull-down on the SLEEP to ensure the motor is off when the power is applied.  DIR and STEP don't matter.

Been studying the arrangement of pins and easiest way to wire the HAT and also the RPi interfacing book.  Here is the result.  The Lens Cover motor driver will be on the HAT and the Focus Motor drivers on a separate piece of stripboard (Veroboard).  One little change for the latter is that I shall separate the data and motor power Gnd lines.  They will be commoned at the power input only.

// Lens Cover Motor
#define DIR RPI_BPLUS_GPIO_J8_07	// GPIO4   DIR
#define STEP RPI_BPLUS_GPIO_J8_11	// GPIO17  STEP
#define STEP RPI_BPLUS_GPIO_J8_12	// GPIO18  SLEEP
#define IN1 RPI_BPLUS_GPIO_J8_29	// GPIOO5  Lens Cover Hall Switch

// Power lines
#define IN2 RPI_BPLUS_GPIO_J8_31	// GPIO06  Dew Heater
#define IN3 RPI_BPLUS_GPIO_J8_33	// GPIO13  Camera Cooler

// Focus Motors
#define IN1 RPI_BPLUS_GPIO_J8_13	// GPIO27  DIR
#define IN1 RPI_BPLUS_GPIO_J8_15	// GPIO22  STEP
#define SLEEP RPI_BPLUS_GPIO_J8_16	// GPIO23  SLEEP

#define M0 RPI_BPLUS_GPIO_J8_35		// GPIO19  Motor A
#define M1 RPI_BPLUS_GPIO_J8_37		// GPIO20  Motor B
#define M2 RPI_BPLUS_GPIO_J8_40    	// GPIO21  Motor C

Been looking into the arrangement of parts in the ASC and concluded that the focus motors stick up too high making a lens cover and the casing, difficult.  I'm therefore thinking of mounting the motors underneath the plate.  The casing will have to be a couple of mm larger but that hardly matters.  Might need to be a bit higher too but not sure yet.  As can be seen in the photo below, the motors will fit below the plate.  This will mean there will be more room for the lens cover and the casing could have a conical top for better draining and less windage.

Thought I had some stripboard but can't find any so ordered some more.  Means I can't construct the focus motor driver board though I have be progressing on the lens cover motor driver connections on the HAT.

Unfortunately, turning the motors up the other way is not just a case of mounting them underneath in the same holes because the camera tube gets in the way so the plate needs redesigning and re-printing so that the motors can be moved further out.  The diagram below shows the problem the motors need moving outwards.  If I keep the same size gears it's simply a matter of pivoting the motors about their axles, or the motor gear can be rotated around the centre of the adjuster screw gear as well.

This diagram shows one of the motors, complete with gear and mounting holes moved outwards centred on the other gear.

Here is the new design for the focus motor plate.  Larger diameter to accommodate the outer motor mounting holes and larger cut-outs to save filament .

Stripboards have arrived   Bit tight for three driver modules as there are just 24 strips - can be done though.

This shows a better layout with connectors.

Waiting for connectors now - maybe they'll arrive tomorrow...

No particular hurry, the moon is going to spoil any night sky imaging for the next several days or more even if the clouds stay away.

Connectors arrived today and I've wired up the focus motor drivers board.

Modified 4 28BYJ-48 5v stepper motors for bipolar connection and attached 4way connectors to plug into the focussing board and HAT.  Gradually getting there   I'm only "running in bottom gear" ATM!

Taking a short break from this project and looking at my weather station instead though I suspect the two will merge at some point.