Re: Crazy Question - What's The Difference Between the PMC8 and a Mini- Computer? #EXOS2 #TECHNICAL #OpenGOTO

Jerry Hubbell - Explore Scientific VP Engineering

On Sat, Jun 27, 2020 at 10:55 PM, Darryl Ellis wrote:
Help me understand.

HI Darryl,

The PMC-Eight Control System is a dedicated instrument designed to control a two-axis stepper motor system. There are actually 2 microcontroller chips in the PMC-Eight system. These are not general purpose processors like what is on a Single-Board Computer (SBC) system. The main microcontroller (processor) is a Parallax Propeller 8-core microcontroller. This processor does not run an operating system. There are 8 separate tasks that each run on a dedicated processor and has access to their own memory space and share information amongst processors through a global memory system. The firmware I created to command and run the motors is written in the proprietary Propeller spin language and also in Propeller assembly language. These languages allow me to control the hardware IO pins directly. You can think of a microcontroller as a signal generator that speaks directly to other hardware such as the stepper motor driver chips used in the PMC-Eight, the serial interface, and USB interface driver chips. I designed and create the output signals from the Propeller chip in firmware to run the other hardware on the PMC-Eight circuit board.

The other microcontroller used in the PMC-Eight control system is the dedicated WiFi processor (microcontroller). The Microchip RN-131 WiFi module is used in the large board Model 2A PMC-Eight system (G11, EXOS 2), and the Espressif ESP-WROOM-02 is used in the Model 1A PMC-Eight system (iEXOS 100). The WiFi processor also has firmware that we load and configure that provides the wireless network protocol stack and serial interface we use to transmit data in and out of the Propeller processor. 

What you are asking is why can't the PMC-Eight operate like an Arduino, or Raspberry Pi? The answer is that these processors are not general purpose computers that run an operating system the way we have them configured in the PMC-Eight system. Having said that, the ESP-WROOM-02 can be configured to run the RTOS operating system if one were to load that firmware into the processor. I did not choose this configuration as all we require is to run a wireless protocol stack and serial interface to the Propeller 8-core microcontroller. The Propeller chip has access to only 64 KB of memory space (EEPROM) with 32 KB of firmware loaded from the EEPROM into system RAM (32 KB) when booted. The ESP-WROOM-02 has 4 MB (32-Mbit) of memory space (EEPROM) to load programs and firmware and provides a file system to store data. This is a more sophisticated processor that can approach but not quite be a general purpose computer in operation. 

If you own an iEXOS 100 system, you could reprogram the ESP-WROOM-02 WiFi module to include the RTOS operating system and build applications install the network stacks and also run a webserver to provide an interface HMI on the network. We have not (as yet) worked on this type of control interface for the PMC-Eight control system. We are currently researching and developing these and other systems that use SBC's and the WiFi modules capabilities but we have not announced any plans for future products based on this technology. We are still ramping up our capabilities in these areas. 

Finally, we provide the documentation and links for our customers to pursue this work for themselves and share as they see fit with the OpenGOTO Community of PMC-Eight customers.

I know this is a bit long, but I wanted to explain to everyone what the system is actually capable of and how we provide "margin" for future capabilities and future improvements.

Jerry Hubbell
Vice President of Engineering

Explore Scientific, LLC.
jrh at
1010 S. 48th Street
Springdale, AR 72762

Author: Scientific Astrophotography: How Amateurs Can Generate and Use Professional Imaging Data
             Remote Observatories for Amateur Astronomers: Using High-Powered Telescopes From Home

Mark Slade Remote Observatory (MSRO) IAU MPC W54 Equipment
Wilderness, VA
: ES PMC-Eight G11 + Telescope Drive Master (TDM)
Scopes: ES 165 FPL-53 ED APO CF, ES 102 FCD100 ED APO CF
Cameras:  QHY174M-GPS + FW, QHY163C
Misc: 3-inch 0.7x Focal Reducer Field Flattener, Filters: Luminance,
Red, V-band Photometric, Diffuser, 200 lpmm Spectral Grating

Software: MaxIm DL 6, Cartes du Ciel, Astrometrica, AstroImageJ, AutoStakkert!

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