Gina's Observatory Roll-Off-Roof Automation

[Gina]

I think I now have enough information and made sufficient decisions to design the electronic circuitry.  Below is a quote from a few days ago which contains most of the information but whilst the lock-down latches and window bolts will be retained there will be no sensing of this condition, I shall rely on my common sense to disengage the clutch when locking down and maybe set a switch to relay this condition to the indoor client system. 

I also plan to have LED indicators on the control panel to confirm that everything is working or if there's a problem.  These would be :-

1. Green - Roof closed - confirms limit switch state
2. White - Roof open- confirms limit switch state
3. Blue - Roof closed from rain detected
4. Yellow - Motor told to run
5. Red - Fault eg. excessive motor current

On 02/08/2019 at 16:49, Gina said:

These are the digital input lines for the Arduino :-

1. OPEN - Push button
2. CLOSE - Push button
3. ABORT - Push button
4. Rain Sensor (relay)
5. OPEN limit switch
6. CLOSED limit switch
7. RPi Open
8. RPi Close
9. RPi Abort

Digital output lines :-

1. M1INA - Motor control
2. M1INB - Motor control
3. CSD0 - Current Sense D0 to RPi
4. CSD1 - Current Sense D1 to RPi

Analog input :-

1. CS - Current Sense voltage

Total I/O lines = 14.  This is well within the capabilities of the Arduino Nano.

There is another input that might be advisable which I discovered whilst testing the motor drive and that's the ROR lock down latches.  There's also the tower bolts on the window.  I could just provide an OFF switch on the control unit but I couldn't trust myself to switch OFF when the roof is locked down.  "Locked down" is another signal that could be sent to the RPi for display indoors.

Edited August 5, 2019 by Gina

[DaveL59]

10 minutes ago, Gina said:

Distilled water will not trigger the rain detector - this is a known fact.  The water needs to contain salts to be conductive.

We will get rain eventually that is a fact.

so true, tis summertime in the UK after all 😉

Was kinda thinking a small amount of distilled in the watering can... should pick up a little contamination that might get detected, but the weather here will usually co-operate every few days lol

[JamesF]

1 hour ago, Gina said:

We will get rain eventually that is a fact.

Tomorrow looks quite promising in that respect at the moment.  Showers all morning, the weather forecast says...

James

[Gina]

I don't really want to use an Arduino Mega so I'm going to look at what I can do with a Nano.  The Nano has 12 digital I/O pins and 8 nominally Analog input pins, 6 of which can be reassigned as digital I/O. 

The LEDs that indicate the state of limit switches can be operated by the limit switches themselves.  This would save current from the Arduino.  The limit switches have independent NO and NC contacts so one pair of contacts can be used as input to the Arduino and the other to power the LED.

LEDs for "Roof Closed due to Rain Detected" and "Fault" will have to be controlled by the Arduino.  The Yellow "Motor Powered" could be run from the motor  power lines and would be useful to show that the motor was powered ie. there is voltage applied to the motor.  To allow for the reversible motor voltage, the LED could be run from a full-wave rectifier.  Alternatively, two LEDs could be used, each between one motor wire and Gnd (with series resistor, of course).

To be continued...  (Tomorrow)

[Gina]

In addition to the roof controller, I shall need another output from my main power distribution box.  I could just run the roof power from the mount output but I really want the supply to the mount and roof control separately fused.  So ideally I shall want to design and build a new power distribution box.  This is not difficult - just yet another thing to do.  I believe in doing things properly and not skimping - particularly on safety features.

[Gina]

Whilst redesigning my power distribution unit I might as well add a couple of extras I've thought of.  When not using the observatory for some time I disconnect the 13.8v PSU from the battery and turn it off.  I have several digital ammeters and voltmeters in stock and would like to check the battery voltage and also might as well have ammeters for each of mount, imaging rig and roof control unit.  If I have an ammeter for the roof controller, I shall not need an LED for the motor current on the control unit.  ATM I have one ammeter which shows total current to mount and imaging rig - makes more sense to separate them.

[Gina]

Had a shower of moderate rain for the last ten minutes and the rain detector has shown nothing!!  I guess our rain is too clean today.  Rain has stopped now.  More and heavier showers are forecast for this afternoon.

[Dr_Ju_ju]

Hmm, sounds like you may need to get a detector that will fire on pure\potable water as well as 'dirty'...

There are some that utilize detectors that can be fitted to a funnel and can detect the presence of ion's so are very sensitive.

[JOC]

On 05/08/2019 at 08:32, Gina said:

A watering can would contain polluted water but what I really need is real rain.

Could you not fill the watering can (clean, new?) with collected rain water from a water butt?

[Gina]

No need for imitation rain - I have the "Real McCoy"!!

[Davey-T]

Detecting rain when it's already raining seems a bit too late especially swift summer downpours when it can be blue sky one minute and chucking it down the next, would not using one of the many radar rain apps be better to see it approaching and close the roof before it starts raining.

No idea if they can be connected to automatically close the roof though ?

Dave

[Gina]

Just started again and detected it within a minute or two.  Can't be absolutely sure how long as I wasn't watching the PSU at the time - watching Bargain Hunt 😁

That first shower didn't wet the ground - just a few drops, so maybe wouldn't have done any harm.  This one is a lot heavier and the observatory roof is well and truly wet!

[tekkydave]

Ha ha - we were watching BH whilst having our lunch.

 

[Gina]

I think I shall put the electronics for my imaging rig in a waterproof casing.  The camera would not be affected much by a drop of rain though the connections will want protecting.  Filter wheel is virtually sealed and lenses/telescopes wouldn't suffer from just a little rain.  I can arrange that some things be covered to keep rain off.  All this means a light rain shower shouldn't be a serious problem and heavier rain seems to be detected.

[Gina]

Whether some sort of funnel would be a good idea for the rain detector, I'm not sure.  With a fairly strong wind the funnel would shield the rain detector from rain until some ran down the funnel.  A wide funnel would slow down raindrops running down the funnel surface.The rain has eased off to a very fine drizzle and the rain detector heater has dried off the sensor.  There is still a good breeze.  Seems that this rain detector will detect moderate or heavy rain quickly but a fine drizzle could last ten minutes or more before being detected.  Maybe two rain detectors could be used - one with a funnel and one without.  At least a sudden downpour should close the roof.

Edited August 6, 2019 by Gina

[Davey-T]

Will heavy dew trigger the detector ? I sometimes have a puddle from dew running down the mount / pier.

Dave

[Gina]

It has occurred to me that an indication of rain having caused the roof to close is not needed.  If the roof has closed and I haven't closed it then it must have been rain that caused it to close!

[Gina]

5 minutes ago, Davey-T said:

Will heavy dew trigger the detector ? I sometimes have a puddle from dew running down the mount / pier.

Dave

That I don't yet know.  If it does I may need to add a dew heater though not too much.  There is electronics inside the detector which will provide slight heating - 8mA at 12-14v = 100mW approx.

Edited August 6, 2019 by Gina

[Gina]

The difference between a very fine drizzle and a heavy dew...  Could be a difficult one!

[Gina]

One thing that would be possible with remote control is that I could schedule the roof to close when my scheduled imaging run has finished.  (As well as Parking the mount if using a large telescope.)

[Gina]

Had a search for those digital ammeters but no joy.  I thought to myself "oh well never mind I'll just buy some more as they're only a couple of pounds each" but I can only find combination voltmeter and ammeter units and a few voltmeters.  I may find the digital ammeters in time and can do without meantime.  I can get a combo V/A meter for the battery voltage and one of the current supplies.

[Gina]

Nothing done in the observatory today, mainly due to the weather but also because I needed a break from the physical effort.  Far from a wasted day though, apart from the rain sensor tests, a day of rest is needed now and then plus some electricals sorted out.

[Gina]

If I can arrange a digital ammeter for the roof controller I can dispense with LEDs to indicate motor current.  I can make use of these for showing the motor is connected to a power supply.  I don't need the LED to show that rain has been sensed as mentioned above.  Consequently, my plan for LED diagnostic indicators is as follows :-

1. Green - Roof closed - safe from rain etc.
2. White - Roof open to the sky
3. Blue - Motor supply set for closing
4. Yellow - Motor set for opening
5. (Red - not used)

Green and White LEDs can be connected to limit switches with series resistor whilst the Blue and Yellow LEDs can be connected from motor terminals to ground (again with series resistor).  No LEDs would be connected to the Arduino.  LEDs could be run at 10mA so with 12-14v and LED voltage drop of around 3v, a 1K resistor will be suitable.  With just 100mW dissipation, quarter Watt resistors will be fine.

The motor current will still be sensed to feed to the remote control and the indoor INDI display.

[whizzbang]

if your there to see the LEDs, isn't it better to just run out to close the roof? i love the idea but isn't it getting a bit complicated?

[Gina]

The LEDs just provide local diagnostics of any problem.  I agree that I will have remote indication of some things and that I can close the roof remotely assuming everything is working correctly but my imaging runs usually go through the night and I go to bed to leave everything operating automatically.  Rain detection means I can image even if there's a possibility of rain.  Many times in the past I have been unable to image because of a remote possibility of rain later in the night.

To make things clearer, there are two scenarios.  One is that everything is working and I can open and close the roof locally or remotely and automatically close if rain is detected.  The other is that the roof doesn't move when it's supposed to and something has failed.  This is when the diagnostic LEDs come into the picture.  To add these four LEDs takes very little effort when the unit is built but diagnosing faults later would require taking the lid off the unit and testing with a DMM while trying to operate the controls.  Too many times I have found I need three or four hands to fault-find.

Edited August 6, 2019 by Gina