This project is an implementation of a simple Digital Setting Circles, that evolves from my previous DSC project, but now using an inexpensive optical encoder (and GT2 timing belt+gear) instead of the magnetometer.
This DSC achieves the following:
- Easy and inexpensive to build, for a DIY maker or Arduino enthusiast.
- Can be attached to dobsonian mounts, included tabletops.
- High resolution: 10.200 counts per revolution (compare to the 11.748 counts per revolution of the SkyWatcher Goto Dobs)
- Instead of a wired handheld control, it communicates with Android/iOS apps like Skysafary 5 (plus or pro), DSC-Browser and others via WiFi.
My prototype is a removable version installed on a Zhumell Z114 tabletop:
You can see I'm using a woodworking clamp to affix the encoder in the position required to have proper tension in the timing belt. This way, the DSC is very easy to remove from the scope without leaving any permanent marks.
$3.05 NodeMCU ESP8266 development board (version 12E) (link)
$4.20 LSM303DLHC sensor module (link)
$17.99 Signswise 600p/r Incremental Rotary Encoder DC5-24v 6mm shaft (link)
$9.99 85 teeth GT2 timing pulley 10mm shaft (link)
$0.82 20 teeth Gt2 timing pulley 6.35mm shaft (link)
$1.05 GT2 timing belt (size depends on your telescope size), I used 400mm for the Z114 (link)
Subtotal parts cost: $37.1
Add some solder, cables, a 5V power source, a couple resistors, and screws for attaching the encoder to the base whichever way you want. A maker can build this DIY DSC for much less than the cost of two high resolution optical encoders and a NexusDSC.
The key to this new version of my DSC is the use of an inexpensive optical encoder for azimuth. The $17.99 encoder I used has 600ppr, which using quadrature produces 2400 counts per revolution, which would not be engough for a DSC, but using GT2 timing pulleys of 85 and 20 teeth (for a ratio of 4.25 to 1) we can now get 10200 counts per revolution on azimuth, for just a fraction of the price of a 10k encoder.
This is how the GT2 pulleys and belt look in the base of my Z114:
For simplicity and cost savings, altitude is driven by the same high-res accelerometer I used in my previous DSC, the LSM303DLHC which has more than enough resolution to match the azimuth encoder.
The microcontroller is a very inexpensive ESP8266, I used the nodeMCU variant which seems to be tolerant of the 5V inputs from the encoder. You can use any 5V power source you want, I'm using a power bank:
The large box is the power bank, the smaller box is housing the main circuit with the ESP8266.
To use it you just connect your tablet to the WiFi access point created by the device, configure SkySafari 5 Plus (or Deep Sky Browser, or other program) to connecto the IP address of the device (by default: 126.96.36.199 port 4030), select "Basic Encoders" for Telescope Type, and voilà! SkySafari is now connected to your scope.
I've published the schematics for the circuit (which is really very simple) and the source code for the microcontroller on GitHub.
Edited by Adun, 26 August 2017 - 08:01 PM.