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I thought it would be useful to summarise my experiences in trying to track down and cure communications problems with my EQ6 Pro mount when used under ASCOM/EQMOD control. It might help other users who have similar issues, and point to areas for investigation. The help from the EQMOD, ASCOM and EQ6 Yahoo forums was also invaluable.
The equipment setup is a Nettop ZBOX HD-1D11 (Atom D510 @ 1.66GHz, 2GB ram, 64GB SSD) running XP, Ascom v5.5.1, EQMOD v1.23e, connected via USB to a Hitec EQDIR module, which connects direct to the EQ6 input. All other equipment was disconnected during the tests.
The typical fault in EQDIR mode was the occasional comms loss just after connection, and an almost guaranteed comms loss during a slew. This reduced to an occasional single event comms loss when using the handset in PC direct mode (USB-Serial adapter – Handset port), which didn’t provoke a stop command. The communication status can be seen if you click on the ‘display +’ button (top left) on the EQMOD panel, and/or the Ascom symbol which opens a comms terminal window. The mount worked perfectly normally if you just used the handset.
The first suspect was the prolific chipset used in the Hitec EQDIR adapter. Prolific chipsets are not noted as the most reliable by the EQMOD designers, and XP did not allow access to the latest drivers (3.3.11.152, which are for Vista onwards). I upgraded to W7 on the nettop and downloaded the latest drivers from prolific, but it made no difference. I then tried a Shoestring Serial EQDIR module with an Astronomiser USB-Serial adapter, but this also used prolific and had the same problems. Next up was a FTDI based USB- 5V TTL cable, same problem. Finally, the gold standard, a Keyspan USB-Serial adapter, which unfortunately also gave the same communication issues.
So the problem was probably not associated with the computer – EQDIR link, so I started to look elsewhere. I had noticed that the red LED on the mount flashed occasionally during slew. In my case I was using a free ‘12V 6A’ PSU supplied with the mount, through an extension cable to the mount. The handset said I was getting 11.7V, dropping to 10.4V during a RA+DEC fast slew. This gave the flashing LED during the slew. When I removed the extension cable I got 12.2V static and 11.7V during a slew, and a solid LED. However, I still got the communication failures. I removed the power connector at the mount and measured the voltage with a multimeter held directly against the jack plug. This showed the voltage varying from 12.1 – 11.3V over a period of about a second or so, even with nothing connected.
Many people use this mount and EQDIR/EQMOD with no issues, and many people use a power tank to power it. Lots of people also use laptop style power ‘bricks’ to power the mount. Power tanks/batteries run at about 13.8V, so I wondered if the low voltage, or the cyclic nature of it, was contributing to the comms error. I replaced the PSU with a stabilized supply set at 13V and the comms errors have gone away! If I were to guess I would say the cyclic power fluctuation triggered a comms error during the voltage ‘dip’. This would be aggravated during a slew since the overall voltage dropped when the motors ran. So finally I believe the problems were caused by a faulty power supply, and cured with a good regulated supply.
The supplied power brick ran the mount perfectly with just the handset, so you would never notice a problem under these conditions. Also, if the mounts were not tested with EQMOD/EQDIR prior to delivery, the supplier would never notice it either. The problem only appeared during direct EQMOD/EQDIR control. The problem would also not occur if you used a power tank or battery, since they tend to run at about 13.8V. Of the USB-Serial adapters, they all subsequently proved to work. The Keyspan is probably best, and it comes with lots of useful diagnostic software. However, I now used the FTDI based USB- 5V TTL cable as my EQDIR interface, very cheap and reliable.
So if you get comms issues with EQMOD, check your power supply first, then move on to the various bits of hardware/software. Post queries in the various forums. The cable based USB- 5V TTL EQDIR solutions are a good method for linking your computer to the mount. To have a reliable EQMOD setup allows you to realise just how good this software is for mount control.
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