Balcony resurrection for the coming season

[perfrej]

Good morning, fellow DIYers!

The Swedish summer season is a total loss when it comes to astro things - no darkness between mid May and mid to late August. As the dark season is approaching I needed to resurrect my balcony observatory so I started with the electronics cabinet. The one I had last season has been changed for Provence and is now part of Jonas Grinde's rig down there. I needed something new and figured I should go at least part "industrial" and use DIN rails.

Parts description

1 Cabinet

This is a Rittal IP65 cabinet in steel with a good door seal.

2 Main power supply

DIN rail mounted switched power supply 13.8V 10A. This PS powers the entire cabinet and keeps the battery charged, and is powered from a mains connection.

3 DC/DC converter

DIN rail mounted 12V to 24V switched converter 4A. 10Micron mounts are run off of 24V DC (actually a little more is better so I have adjusted this to 28V). The converter is powered from the new "control device" (8).

4 Computer

A tiny Gigabyte computer with quad core i3 processor, 4GB of RAM (will increase this to 8GB if needed) and a 256GB Intel SSD. It runs a 64-bit version of Window 7. The only connections to the computer is power, LAN and one USB. Unfortunately, it requires 19V DC, so I had to add item 7.

5 10Micron control box

Mounts from 10Micron have a detached control box to which power, LAN (or serial), handbox and mount is connected. I have ordered and received a special box-to-mount cable that is 2.5m long instead of the standard 1m in order to be able to mount the box in the cabinet. This box is powered by item 3, the DC/DC converter. It also has a power switch that is controlled from item 8.

6 5-port gigabit switch

The computer and the mount are both LAN connected, so I modified a metal case Netgear 5-port switch to include a DIN rail holder.

7 DC/DC converter

19V 120W 12V to 19V converter. Unfortunately, the cost and trouble of obtaining a DIN rail mounted converter was prohibitive so I used my trusted "car adapter", first taken apart and fitted with a DIN rail holder.

8 Control Device

This is a new design of mine that I made for myself with a number of nice features (see below). It controls all things electrical in the cabinet (more or less)

9 Connections

DIN rail screw terminals connect the devices external to the cabinet, including the battery.

The new control device contains a 7-port USB HUB with 5 switchable, one always on and one internal ports. The internal port is connected on-board to an FTDI USB to serial device that is used for device control. Five 12V switchable outputs with software fuses that disconnect the device electronically if a settable current is exceeded. All can function as PWM outputs for dew heat and can also be logically linked to a USB port. A linked 12V output is switched on and off in parallel with its USB port.

All USB ports have proper 0.5A current limiting that will disconnect the port should the device connected to it fail. Switching a USB port off and back on the way this device does is equivalent to a physical unplug and re-plug. This is crucial to me as I will use my stuff remotely.

There is also a stepper motor driver for focusing on the board, and I have used very exact timing with interrupts in order to be able to drive the steppers at their full speed. My Lakeside motor on the Takahashi is set to step every 3 ms, so a 1000 step move is executed in 3 seconds. It can also micro-step 2, 4 and 8 times and has stepper motor hold capability. In essence, it drives every conceivable stepper that is not unipolar. On I side note; I took off the cover from a Lunatico unipolar stepper and found that cutting a shorting trace on the cable solder point converted it to a hybrid stepper. Cool, as I do not like unipolar steppers.

Board processor is an Atmega 328P and the "firmware" is written entirely in C++ with the Arduino development environment. I run the processor off 3.3V so I had to revert from 16MHz clock to 12MHz, but it is still blazingly fast. An ASCOM driver for Switch and Focus functionality is almost complete.

I will stress test this cabinet on the balcony for a month or two and then - time allowing - move it to my second remote location in the Stockholm Archipelago. At that point I need to rethink my balcony setup. Current plan calls for adding homing sensors to my belt-and-bearing modded NEQ6. A third 10Micron feels a bit over the top

So, as per now, my balcony setup contains the new cabinet, my GM1000HPS, my Takahashi FSQ-106 EDX III and the SBIG ST-8300M with an SX wheel with Baader unmounted filters. I'll run it with CCD Autopilot to begin with. This is so much fun!

All the best,

Per 

[Gina]

Excellent

[perfrej]

Thank you, DIY guru!

/p

[Singlin]

Per I could not find an electrician in the whole of my county (valle D'Aosta) that could produce something like that let alone design it.

Fantastic!

[Gina]

I like the idea of a built-in tiny computer   I'm setting up a tiny remote controlled imaging station myself though remote in my case is just a few metres

[perfrej]

Thanks, Singlin - it is an Italian mount after all and it deserves the best

Gina, having the PC in the actual control point of the observatory is key. It generates just the right amount of heat for winter conditions (I have run down to -30°C at times without glitches) and moves the "remotenessness" to a single RDP connection. If the net dies on you the thing keeps doing its thing and you get the images when it comes back online. I use Goodsync Pro, a very competent enterprise class syncing software, for the actual image transfer to my home systems.

Even though you are only a couple of meters away from your setup it makes sense to treat it as a fully remote system.

/per

[NickMorris]

Very, very nice indeed Per,

You mentioned a battery in the write up but I couldn't see one inside.  Presumably you are going to use a large 12V battery externally just in case the mains power falls over?  If so, will it just be wired in parallel to the 12V output from the mains 230v > 12V supply?  Also there is a DB9 serial connector lurking at the bottom right, is this for a weather station hook up?

Have you got any copyright on this design as I feel an RS order coming on.......

all the best

Nick

[perfrej]

Thanks, Nick!

The battery is a Sonnenshein 40AH professional battery. It is a battery of choice for important installations such as metro and railway control systems. In fact, the battery I use comes from the Stockholm Metro; they change batteries every four years regardless of shape and I managed to get hold of a couple in very good shape. They take deep discharge really well.

It is placed in the cabinet vicinity, connected in parallel with the 12V (actually 13.80V calibrated) output of the main power supply. As you can see on the spec sheet on the battery, it is designed for float charge at 13.80V so that is how they are normally used.

The DB9 is for the AAG Cloudwatcher unit. It takes power from the screw terminals and serial comm via the DB9, which in turn is the business end of an Aten USB to serial converter that connects to the HUB.

I will not let go of the design at present, and I will not manufacture it. Consider it an internal breadboard, albeit on a real PCB

All the best,

Per

[Gina]

Thanks, Singlin - it is an Italian mount after all and it deserves the best

Gina, having the PC in the actual control point of the observatory is key. It generates just the right amount of heat for winter conditions (I have run down to -30°C at times without glitches) and moves the "remotenessness" to a single RDP connection. If the net dies on you the thing keeps doing its thing and you get the images when it comes back online. I use Goodsync Pro, a very competent enterprise class syncing software, for the actual image transfer to my home systems.

Even though you are only a couple of meters away from your setup it makes sense to treat it as a fully remote system.

/per

Thank you Per   Interesting   I have been thinking of making my WF imaging station (aka "Gina's Mini Widefield Imaging Observatory") fully remote even to the point of using a roll off roof but I do wonder if this amount of complication is warranted even if it does make it more fun

[NickMorris]

Nice one Per,

So it's ok to keep the battery with 13.8V tricking into it (not use a special charger) ?  The design copyright joke was referring to the whole IP cabinet layout not your Astrobox Mk2!  I have a ton of din rail stuff in my toolbox from the lighting dimming racks we build at work, so may attempt something similar albeit without the Astrobox.  I have a separate starlight focus hub, Kendrick dew heater controller and din rail USB3 hub - not as neat or controllable as your astrobox but will get an ethernet switch to control 10 micron box on/off, CCD, focus hub and dew heater power switching.  As for adjusting the dew heater level and plug/unplug usb, I guess I'll just go out onto the flat roof.....

Now I just need to figure how to do temp and pressure sensing, without stretching to a Davis weather station.  Was also wondering how Meinberg NTP would work over a 3G connection when I take my gear to a dark site?  Maybe a precision handheld GPS?

All the best

Nick

[perfrej]

Yep, float charge, per definition, is the voltage at which the battery compensates for self discharge and other losses; hence stays full. It is a dead slow and not so good method of charging a discharged battery, but that will not happen often. Unfortunately, float charge voltage varies with temperature, but I am willing to take a small chance on that. Lower temperature means more voltage is needed, so ideally this should be temperature compensated...

Meinberg should work fine over cellular networks but I do not think that you have to compensate live. Just get a good sync initially and then disconnect. The only "precision" you can get out of a GPS is a 1PPS signal (one pulse per second). It should be time-aligned properly to a few hundred nanoseconds, but how would you use it? You would need special hardware.

I use a temp and pressure device from Bosch. It communicates via I2C and can be directly connected to all my toy devices as I have that bus everywhere. It is called a BMP-085. Attached.

/per

BMP085_DataSheet_Rev.1.0_01July2008.pdf