A positioner to accompany the Pace MSS-series
( and, probably, older series as well)

Once upon a time I bought a satellite receiver. At first just for viewing the Sky-channels.Since Sky decided at one point to improve the security on their viewing cards and it was no longer possible to view their channels, I had to look for an alternative. I found this alternative in the Scandinavian channels, located on Thor and some other satellites on 1.0 and .8 degrees west.

So I bought a D2Mac decoder and turned my dish onto 1 degree west instead of Astra. Lots of fun. But after a while the desire came up to look at some channels on the Astra as well, so it turned out that I had to turn my dish every now and than by hand. Since positioners are quite expansive, (compared to their task), I decided to build my own.

At first I figured out a mount on which my dish could be motorized. Mounts aren`t that expansive, but I felt that I easily could build this myself as well. The result worked out very (VERY) good. I will publish this later on, every body that knows how to switch on a welding-machine (believe me, that`s all I know of welding), should be able to build one him/herself. The total amount of money spend on the mount is less than Fl50,- (approx $25).
Now a had to think of a way to motorize the thing. I`ve thought  long and hard on this but, finally I went to a satellite shop an bought me an actuator. Maybe someone has a good design of building your own actuator, I haven`t.
 

The design

After building the mount and fitting it, I quickly build a supply to control the actuator. Two switches and a transformer with a greatz did the job.
But this was not my goal. I wanted to make a real positioner. One that figured out the position of the current satellite and was able to store positions. If Pace could do that, why couldn`t I ?
Since every modern actuator is fitted with a reed-switch that is operated by a magnet on the axe of the actuator, determing position was not the problem. I use a I2C-EEPROM to store positions. The whole positioner is based on a 89C2051 microcontroller.
The (Pace) receiver sends serial data throughout the decoder-scart, on which a positioner can be connected. The real problem here was to determine the protocol used by the receiver. Here the powers of the Internet gave me a hand. Many thanks to Antonio Cunei, he provided me with the right information on the protocol.

The results:
 

The schematic:

(shift-click to download)
 
 

The 89C2051-program:

Both source and hexfile, version 1.5 are in a zip-file. You need to program this into a 89C2051 in order to get the thing work.
Source and hex file are free for non-commercial use.
 
 

The PCB

Not ready for publication yet.
 
 
 

Final thoughts

This design is based on an Atmel 89C2051 because I have much expirience with this type of microcontroller. But (big but) if I had chosen for a different popular microcontroller, the Microchip 16C/F84, the number of parts would be dramaticly decreased. The 16C/F84 has EEPROM on-board, causing the external EEPROM to be obsolete. The 16C/F84 has active-high outputs (instead of open-collector), making it possible to exchange the buffers-chip by two transistors.
Above these things, the 16C/F84 is cheaper, and more easy to program, programmers all around.
Of course the 89C2051 is a very nice chip, its more advanced than the 16C/F84, but that is just not what we need here.

Further on, I`m not really happy with the relay-configuration, this can be made simpler, using simpler relays.

For questions, suggestions and comments, please mail me at gradtje@geocities.com 1