MountOne | Electronics.

Don't Panic!

This guide is 99% images.

Index.

Electrical Components.

The MountOne Hardware Pack includes the following required electrical components.

    • 1 x Power Slip-Ring.
    • 1 x Signal Slip-Ring.
    • 2 x DC Female Sockets
    • 1 x DC Male Plugs.
    • 1 x DC Male Angled Plug with 2m cable.

Parts you will need to source yourself.

    • OnStep MaxPCB4.
    • Teensy 4.1.
    • 2-4 Stepper Drivers (I use TMC5160s).
    • ESP8266 Module.
    • 5v Power Module.
    • Heatshrink & Connectors.

If you have downloaded the MountOne CAD Pack, there is a full BOM inside. 

Power Ratings.

The Power Slip-Ring (RA) is rated for 10A. The Signal Slip-Ring (DEC) is rated at 2A.

The Lowest rated cable is 1.5A. This is the cable that comes with the DC Male Angled Plug with 2m cable. This cable is used through out the build and will be sufficient for the four astrographs I have developed.

During testing with the astrographs and the system connected to a desktop power supply, the power draw did not exceed 1A at 24V.

The system is designed around 24V, if you use a power supply with a lower voltage, 12V for example, you will need to recalculate and perhaps upgrade some of the components and cables.

Cable Configuration.

The information below pertains to the function of the coloured wires used in the Slip Rings included with the MountOne Hardware Kit.

  • Red / Black - Power.
  • Orange / White - UART (Tx/Rx) from the MaxPCB4.
  • Light Blue & Brown / Purple & Green - Stepper Motor Twisted Pairs.
  • Dark Blue & Yellow / Pink & Grey - Stepper Motor Twisted Pairs.

We will go into deeper detail the precise wiring during the MountOne Assembly Documentation.

Note : The MaxPCB4 is sensitive to bad wiring, and if you get the motor phases or other connections wrong, you will very likely destroy a Teensy and a Raspberry Pi.

I learnt this the hard way so you don't have to.

DC Slip Ring (RA).

The DC Slip Ring is easy to identify, it only has two (four?) wires, red & black, coming from it. You'll also need a DC Female Socket. Note for this first part we shall be using the wires protruding from the larger diameter end of the Slip Ring.

The washer and nut can be removed from the DC Socket and discarded.

Slide a larger diameter length of heatshrink onto each wire, followed by a slightly narrower length.

Solder the Red (Positive +) wire to the DC Socket, and the black (Negative -) wire to the longer outer connector.

Slide the smaller heatshrink over the soldered joint and heat shrink, then slide the larger tube over and heat shrink too.

The double layers of heatshrink will help reinforce and insulate the joints.

Next, we shall fit the DC Male Jack and DC Angled Male jack to the other two cables.

Remove the casing from the DC Jack.

Cut approximately 60mm from the length of the two wires. Strip and tin the end of the wires from the Slip Ring.

Cut the DC Male Angled Plug leaving approximately 110mm of cable behind it. Strip and tin the end of the wires.

From the 5m of cable that came with the angled DC plug, cut off approximately 140mm, strip and tin both ends.

Note that one of the two wires has a white stripe running down its length, this is to indicate it is for connection to Positive (+) connections.

Solder the positive cable to the centre pin, and the negative to the outer pin. Carefully crimp the cables.

Replace the casing.

We shall now connect the two DC Plugs to the Slip Ring.

Split the cables approximately 50mm from the end.

Install a single, larger diameter length of heatshrink over BOTH cables on the Slip Ring, followed by individual smaller diameter heatshrink on each cable.

Holding the two cables with white stripes down them, solder them to the red positive (+) cable from the Slip Ring.

Repeat this process with the three negative (-) cables.

Slide the small individual lengths of heatshrink over the joints and heat shrink.

Slide the larger diameter heatshrink over the two wires and heat shrink too.

The DC Slip Ring (RA) is now complete.

Signal Slip Ring (DEC).

The Signal Slip Ring is a little more involved as it has to pass power and data between the OnStep PCB and the Astrograph.

You will require connector housings and connector crimps. The wire-to-board connectors are standard 0.1" style connectors for the headers on the MaxPCB4. The wire-to-wire connector, which connects to the Astrographs, can be anything you'd like. However, for this guide I have chosen to use standard 0.1" connectors throughout.

Molex MicroFit 3 would be a nice alternative.

Starting with the smaller diameter set of wires from the Slip Ring, solder the DC Female Socket to the red (+) and black (-) wires. Be sure to use heatshrink.

Cut the ends of the wires to length, approximately 4mm is fine.

Crimp female connectors to the remaining 10 wires.

Firstly, begin by inserting the white and orange wires into a two-pin housing.

Next, the light blue and brown wires go into a 4-pin housing. The position of the wires in the housing is important. I have also twisted the wires together.

Add the green and purple wires to the same 4-pin housing. Note again their position. They too have been twisted together.

To another 4-pin housing add pink and grey wires, similarly twisted and correctly positioned.

Complete the set with the yellow and blue wires.

This will end the assembly of this side of the Slip Ring.

Next, the larger diameter cable group.

Affix female crimps to all 12 wires.

To the top of a 2x6-pin housing, add the red (+) and black (-) wires as shown.

Below those wires, add the orange and white wires as shown.

To the side with the red and orange wires, add a twisted pair of blue and yellow, as shown.

Followed by the pink and grey to match the set on the other side of the Slip Ring.

Flip the housing over and install the remaining four wires as two sets of twisted pairs, matching the other housing.

This completes the assembly of the Signal Slip Ring (DEC).

While the exact wires and their position in the connector housing is not strictly important, it is important that they are wired to the correct I/O on the MaxPCB and attached astrographs.

Getting these connections wrong will break things.

OnStep MaxPCB4.

MountOne uses the OnStep MaxPCB4. These can be purchased from https://graydigitalarts.com/ who are an authorised OnStep Dealer. We have worked with GrayDigitalArts for many years and they have put together a kit for The MountOne.

Head over to their site | https://graydigitalarts.com/product/hexaxes-mountone-pcb/

Please read the MountOne Software Documentation before completing this section.

When assembling the MaxPCB4, please follow the guidance and instructions on the OnStep Wiki.

I have chosen to do the minimalist of installs and left off the buzzer, RTC battery, LEDs, wire terminals, and 15-pin D Sub-Miniature. I have chosen to go with 0.1" pin-headers for all I/O. 

I have added an ST4 terminal too, this is not technically necessary.

Note the 2-Pin header on the D Sub-Miniature (JP1), this is important as it provides I/O for the UART communication between the MaxPCB4 and astrographs. It is a required connection.

Raspberry Pi Options.

The MountOne Astrographs are all designed around the Raspberry Pi 5, the Raspberry Pi 5 Official Active Cooler, and the Raspberry Pi Official M.2 HAT.

If you are in a bad Wi-Fi area, the combination of the Raspberry Pi Compute Module 5 and Waveshare's CM5 IO Base B allows for an almost identical setup, but with the added bonus of an external Wi-Fi antenna. This setup is slightly more expensive, but well worth the extra money if you have connectivity issues.

I have created additional CAD for the PineFeat Lens Controller Astrograph which integrates the Wi-Fi antenna into the astrograph's housing. If there is sufficient demand, I can make similar modifications to the other astrographs.

Alternative Parts List.

  • Raspberry Pi Compute Module 5 (Lite).
  • Raspberry Pi 256GB SSD.
  • Raspberry Pi Compute Module 4/5 Antenna Kit.
  • Waveshare Mini base Board B (CM5-IO-BASE-B).
  • Waveshare Cooling Fan For Raspberry Pi Compute Module 5 (CM5-FAN-3007-B-5V).

These should be available from multiple sources.

Continue to the MountOne Assembly Documentation.

Back to the MountOne Documentation.