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Contains:  Gear
How to safely shut down a 10Micron mount on power loss, 





    
        

            Tony Cook

How to safely shut down a 10Micron mount on power loss

Description

My solution was to use a OpenUPS2 uninterruptible power supply board with some interfacing circuits to link it with a 10Micron mount controller box. See here

Above is shown an OpenUPS2 board with three LiFePO4 batteries fitted along with diagrams of the circuits used to interface it to a 10Micron controller. This set up is designed to safely shutdown a 10Micron mount in the event of a main power loss. This avoids the possibility of an unexpected sudden shutdown that may result in corruption of stored data (such as pointing models) or even the mount firmware.

The top occupied socket on the OpenUPS2 board is the boot/shut down trigger output. This is normally intended to be connected to the boot/shutdown header socket found on PC motherboards. However for operating a 10Micron controller the top relay circuit allows the UPS shutdown output (effectively working as a voltage controlled low current resistor) to operate a "volts free" relay that shorts the two contacts of the 10Micron "Ext" jack socket to initiate shutdown. [ERRATA - the circuit diagram is missing the back EMF protection diode across the relay coil]

The lower occupied socket is the USB connector which serves two functions. First is data communications to set the UPS parameters such as output voltage and various time delays before the shutdown trigger is produced as well as for monitoring the UPS running state (via a Windows application). Second is to use the presence/absence of the USB 5v to monitor the on/off state of the controlled computer. This is important as the UPS uses this information to suppress the shutdown trigger if the computer is already off. Otherwise on power loss the UPS may accidentally boot the computer instead. As the 10Micron controller does not provide a USB output, the lower circuit uses a simple photo Darlington switch to monitor the 10Micron red power indicator LED and drive an "Arduino" relay board in response to the LED state. The relay switches on/off a 5 volt supply output using an off-the-shelf >5v to 5v DC/DC buck converter connected to the 24v UPS power output. The UPS power output is set at 24 volts via the UPS configuration app to power the 10Micron controller. The peak sensitivity of the selected photo transistor is in the near IR and gives a reliable response to red LED light.



Above is the OpenUPS2 board in its box with the cover removed and LiFePO4 batteries fitted.

The left front of the OpenUPS2 box has the boot/shutdown cable (yellow plug) that connects to the "Ext" socket on the 10Micron controller. The UPS uses this to initiate shut down of the mount 3 minutes after power loss. The time delay is to cater for a temporary power loss.

On the right, the red/black cable pair is the 24v output that is connected to the power input of the 10Micron controller.

A voltage and current display is fitted to the front panel of the UPS box. Finally on the front top left is the UPS status LED light. This is continuously on when external input power is consumed, slow blinking when using battery power and rapid flashes when the shutdown signal has been sent. Once the 10Micron controller is shut down, the photodetector turns off the 5v USB input to the UPS and the UPS immediately shuts itself down.

To the right side of the UPS box is is the black box containing the circuit that switches on/off a 5 volt supply to the OpenUPS2 USB input in response to a photo detector fitted over the 10Micron on/off indicator LED. The rear side of the black box has the 5v USB output that connects to the OpenUPS2 USB input, the front left is the 24v supply input from the UPS power output while the front right is the cable that connects to the photo detector .



The 10Micron controller with the 24v power cable (red/black pair), the shutdown cable (yellow jack plug) and the power LED indicator monitor probe (green sheathed cable)



The photo monitor probe (green sheathed cable) removed from its holder fitted over the LED power indicator.



A suitable DC/DC buck convertor used in the photo detector circuit



A typical "Arduino" relay circuit board used in the photo detector circuit to switch the USB 5v power on/off

Comments

Author

Tonk
Tony Cook
License: Attribution-NonCommercial-NoDerivs Creative Commons
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How to safely shut down a 10Micron mount on power loss, 





    
        

            Tony Cook

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