astronomy5

The dome drives were controlled through large DC relays. I replaced these with a Polulu PWM motor controller which allowed for much smoother motion with far less building shaking (the dome is over 1000 lbs), speed control down to zero and far more accurate dome positioning. The Polulu 18v25 is a very affordable and superbly flexible controller that allows for control in many ways, one being by virtual comm port (VCP) over USB. You'll find here a sample bit of code. The four motors run off of 10 VDC and draw on average 15 amperes in total.

Hydreon has an excellent and very affordable rain sensor, the RG11 that is completely sealed, heated and has both a relay and a chatty RS232. I wrote code to pick up the data here. It uses infrared to detect water on its surface, and can detect individual drops, dew and frost. The method is the same as done for car windshield rain detectors.

The observatory's dome was tracked by a barcode reader that senses barcodes about the dome for absolute position, and an encoder for velocity and precise positioning in between barcodes. However, I always wanted to use a magnetometer and gyro instead but they were too expensive back when - in comes the Phidget spatial 1044. The dome's Phidget SBC handles the 1044 and uses two horizontal magnetometer axis, and the vertical rate gyro. The arc tangent of the normalized magnetometer readings provide the absolute portion, albeit noisy (and thus filtered) and the gyro rate is integrated into a position that is high pass filtered, the two summed provide clean absolute position. Although the 1044 is 140$, the barcode reader, USB serial and Phidget encoder it replaces are over 200$ and require more maintenance. Magnetometers are affected by metal in the vicinity, so it is best to place it such that it's *vicinity* mitigates this otherwise one is in for complex compensation. The magnetic compass can vary up to 1 degree over a few hours, although usually less, so the dome position can be off by as much, therefore an *at park* or home switch can serve to ensure the dome parks or homes for closure.

Nearly 30 years of working on imaging and automation, I yearned to return to visual astronomy. I realized that I had not used star maps and star hoping in so many decades. As my homemade 8" newtonian was stored in the barn, I dug into bins and found all the original parts and put Cassiopeia back together. I built an 8'x8' platform with pier and installed her, no GOTO, just motors to slew and follow the stars, and a motorized focuser to prevent the jiggles. While I'm checking the sky through her, the automated observatory 40 feet behind me chatters away! BIG SKY! note - this was the previous property near Dalkeith, Ont.

Domes with twin slit doors that do not use a single circuit of chain or cable to open and close them can jam if the upper or lower drive mechanism don't follow correctly. This could lead to disaster! Thus I've used over the years string pots, sonar and finally laser ranging. Here is shown the laser which provides readings about every 0.6 seconds over USB with virtual com port. String pot can sag, break, get iced up, blown by the wind, whereas sonar doesn't provide reliable and consistent readings due to improper reflections, often changing with temperature and humidity. BUT, the unit won't operate under -16C, so I switched to "time of flight" VL53L0X laser devices over I2C on an RPi zero using Python and sockets.

The in dome cameras I've had over the years always had infrared floods on them, which always worried me as they could spill into the optics. In late 2019, I purchased Raspberry Pi wireless Zero, NoIR cameras and IR floors, fetch free 3D print STLs, and put the lot together. I also wired up a GPIO of the RPi onto the CDS (light detector) of the IR floods so that I could shut them down when no image was being taken. Through Linux bash scripting, the cameras take a very short image every 5 minutes, or when the dome/scope software commands them to, usually during scope and dome slews, aperture opening/closing about every second, so I can watch the goings on in the domes. IR intrusion is virtually nil! 40$ for each camera kit.