Project:
Nikon D800 for astrophotography ?

Contents:

1. Nikon D800 overview
2. Adapter Nikon to Pentax 645
3. Lid, Dove tail, Tube ring
4. Focuser mechanism, driver
5. Off-axis guide camera
6. Computer module and DC/DC converter
7. DC/DC general triple converters
8. Main bracket
9. Wiring & USB-HUB
10. Test with Windows and APT
11. First Light
12. Balance system
13. Nikon vs Canon, Pentax FA vs Pentax
14. Tilt adjuster
15. KStars/INDI setup for Nikon
16. To be continued

Note:
I take no responsibility or liability for what are written here, you use the information on your own risk!

9: Wiring & USB-HUB

All the devices need some power, a lot of wires will connect them to the power source. The control signal goes through USB cables. I try to hold the cables as short as possible.

Power focus driver:

The voltage reducer sit left to the focus driver. With this I can reduce the incoming voltage from 12 volt to optimize it for the focus driver. 8 volt is told to be a good voltage for low impedance stepper motors. An USB micro cable connect the driver to the computer, it runs under the lens which protect it from tangle.

Computer:

The computer, in this case a Raspberry, get its power from the DC/DC converter built into the bracket. Battery voltage of 13.7 volt is reduced to 5 volt. The black USB cable is from the guide camera, a bug force it to be connected to only a USB 2 standard port. The white USB cable come from the focus driver.

Dew heater power:

As a dew heater I lately have used are of the USB type. Made for camera lenses but has worked very well for me on my telescope. But one problem, too high power, 7 Watt. In my earlier setup I solved that problem by connecting two USB dew heaters in serial. Then the power on each was reduced to 1/4, about 2 Watt. At this new equipment I only need one dew heater so have to solve it in another way. I reduce the voltage from 5 volt to something like 3 volt or lower and I get about 2 Watt. Here is a USB female contact connected to my DC/DC converter.

USB-HUB:

I had a hope that I didn't have any need for an extra HUB. But after adding one device after one another I came up to 6 devices. The Raspberry only has 4 USB ports. I must have a HUB, a small 4 port HUB was what I choose. Even if the HUB is small the cables that connect to it take a lot of space. A special designed bracket let me have it on top of the lens.

The HUB is installed and some USB cables connected. Immediately I found that the space between the USB ports was very narrow. The GPS USB dongle are wide and block the port I need to attach other devices to.

There are two free USB ports on the Raspberry, one I will use to the mount, the other to the Nikon camera.

On the top is the USB-HUB, two ports are still free. The internal WIFI is weak because the cooler screen it off. Maybe I can solve that by solder a short wire as an antenna. Or as I do now, connect a WIFI dongle. But there is a problem, even this device has a very wide USB connector, it's not space enough for it. The upper white USB cable is for the focus driver.

Nikon camera cables:

Nikon doesn't use the USB mini connector, it use the USB3 micro connector. I bought a 90 degree angled cable to make it not protrude so much. I haven't used these connectors much, but I think they are compatible with the older USB 2 micro contact.

Connected to the camera, even if it's angled it protrude a bit too much. Maybe the USB2 micro variant is smaller, even USB2 should be fast enough, 36 Mpix raw images.

A 1/2 meter cable connect in the other end to the Raspberry's USB3 port.

Power splitter:

The power splitter I built earlier I'm very satisfied with. It has built in Volt and Ampere meter which is very useful when there is some problem. It also has three outputs with automatic polyfuses. Here I have made a bracket to mount the power splitter on the mount. With this I reduces the risk of getting problem with the cables when the RA axis moves.

The power splitter mounted in the bracket. Only two power cables to connect when set it up. One for power of the Raspberry and the other for focuser and other extra devices. The mount is always connected on a separate power port, this is the EQ6 mount.

Second power splitter:

I have two mounts, most practical if I have a power splitter on each.

I trashed my older version of the power splitter and built a new with the latest design. Later I can shorten the cables when I have test drive it for a period. The Voltage that feed the power splitter is battery voltage, 13.5 Volt. Main fuse an ordinary glass fuse of 6.3 Ampere, each output has a 2.5 Ampere Polyfuse (automatic).