Gina's Observatory Roll-Off-Roof Automation

[Gina]

I was originally thinking of connecting the limit switches via Schottky diodes to the RPi, then I did some lateral thinking and realised that if I used analog inputs for the limit switches on the Arduino I could use RPi GPIO lines directly if they were ones with an internal pull-up to 3.3v.  The other RPi input from an Arduino digital output will have to use a Schottky diode as logic 1 is +5v on the Arduino.

[Rusted]

That's easy for you to say.. 

You know this is an English language forum, don't you?

[Gina]

It's English Electronics Language - province of us Geeks only 🤣

[johninderby]

Should I be worried that that’s just plain English to me???  🤔

[Gina]

Initial assignment of Arduino Nano pins.  Digital inputs from the 3 push buttons and rain detector, analogue input from Current Sense from motor driver and 2 digital control lines for motor power control.

Edited August 13, 2019 by Gina

[Gina]

I think this could be the final connection diagram though pins on the Nano may be swapped around to make sensible connection runs.

[Gina]

Been checking the RPi GPIO lines and have found 7 that can (or do) have pull-up resistors.   Since I want 6 that is fine.  I shall have to check that any of these have predefined functions that are run on power-up before the code is applied.  The 3 remote control lines don't actually need to be pulled up which may be helpful as there are many more GPIO lines that are pull-down.

I think the Nano can go on the RPi HAT which would save using a separate stripboard and make connecting easier.  It is also safer as it would virtually guarantee that the same Gnd is used for both (as long as I wire up the HAT correctly).

[Alan White]

Bit late for the comment,

but it’s all Geek to me! 😂

 

[Gina]

The lathe spares have arrived so I shall probably get the lathe working today.

LATER...  Replacement layshaft timing pulley and key installed, motor drive timing belt on and lathe working.

Edited August 14, 2019 by Gina

[Gina]

Redrawn main circuit diagram.

Edited August 14, 2019 by Gina

[Gina]

Photo of Arduino Nano on RPi HAT plus diagram of GPIO pins.  The # designations are GPIO numbers.

Edited August 14, 2019 by Gina

[Gina]

This table shows the GPIO pin PullUp or PullDown state on Power-on.

Quote

GPIO#	Power-on Pull	Alternate Functions	Header Pin
2	PullUp	I2C1 SDA	3
3	PullUp	I2C1 SCL	5
4	PullUp		7
5	PullUp		29
6	PullUp		31
7	PullUp	SPI0 CS1	26
8	PullUp	SPI0 CS0	24
9	PullDown	SPI0 MISO	21
10	PullDown	SPI0 MOSI	19
11	PullDown	SPI0 SCLK	23
12	PullDown		32
13	PullDown		33
16	PullDown	SPI1 CS0	36
17	PullDown		11
18	PullDown		12
19	PullDown	SPI1 MISO	35
20	PullDown	SPI1 MOSI	38
21	PullDown	SPI1 SCLK	40
22	PullDown		15
23	PullDown		16
24	PullDown		18
25	PullDown		22
26	PullDown		37
27	PullDown		13

 

[Gina]

Here are my thoughts on the RPi to Nano connections :-

1. SDA and SCL (GPIO 2 & 3) have 1K8 pull-up resistors I've read.  The relatively low value should help reduce interference on the lines to the limit switches.  These could connect to A7 and A6 on the Nano.
2. The control lines from RPi to Nano can be GPIO 22, 23, 24 and be wired straight across to A5, A4, A3.
3. The Schottky barrier diode can go to GPIO5 and D13.

That keeps the connections as short as possible and all on the near side of the Nano.

[Gina]

That now give this as the latest update to the main diagram.

Edited August 14, 2019 by Gina

[Gina]

Been turning the outer groove in the new small pulley.  There's quite a lot of material to remove.

[Gina]

More lathe work on the pulley today.

[Gina]

That pulley has been putting up a pretty good fight.  My lathe is too small really.

[Gina]

According to my earlier posts on 31/01/15 in this thread, I turned the chain groove in the large pulley on my lathe but ATM I can't work out how.  The pulley will fit in the lathe but there's a problem getting any tools far enough out to cut the groove.

Edited August 15, 2019 by Gina

[Rusted]

While I do have a larger lathe the ridiculous cost of international postage would make a complete mockery of any savings from DIY.
Besides, the very low price of plastic pulleys online means you rarely need to get involved in any lathe work.

I usually make such things from three flat disks and simply bolt then together into a sandwich. Birch ply is a favourite material and lasts well.
A jig saw or router set no limits on disk diameter. Sand the disk's circumferences smooth if you like them to look a bit posh.

Scrap metal aluminium is another possibility if you have the tools to work it. Power woodworking tools will cut aluminium with the correct metal cutting blades.
A messy job but leaves your mark for alien archaeologists to ponder such strange human activities after THE RESET.

[Gina]

Turning is proceeding...  Time for a cuppa break...

Edited August 16, 2019 by Gina

[Gina]

I think I'm wasting my time with the lathe.  This pulley is too big for this lathe!

I'm going for a 3D printed pulley.  This is 130mm OD with bore to take a pair of 8mm x 24mm x 8mm ball bearings

[Dr_Ju_ju]

If you have any, print it in PetG….  should make it strong & durable.

[Gina]

Yes, I have PETG - my favourite type of filament for this type of application.

[Gina]

Now printing in white PETG.

[Gina]

With the improved weather I've been able to take the pulley out to the observatory and check it.  Fine for diameter but a bit too wide a groove so have adjusted the design and about to print another.