Background



As a result of the effectiveness of the Star Trekking Activity the Heritage Society was asked by the Manager of Goonhilly Earth Station Ltd. responsible for Education Liaison whether we could create a smaller, more portable version which could be used for Schools visits, and the on-site educational events which are occasionally hosted at Goonhilly. Some of the work could be done by GES Ltd. people if we could implement the activity electronics, so we agreed to help. It was needed for a large schools event early the following year, so the target was possible.





The Display



A person in the Graphics Department working with GES Ltd. was assigned the task of creating the backdrop scene to fit a portable frame which was to be ordered. The night sky was chosen and orbital positions and tracks for some of the better known historical Communications Satellites were obtained from the Heritage Society and passed to him for inclusion on the backdrop. Amazingly, the early Telstar and Relay Satellites are still orbiting the Earth in low orbit, although they are now inoperable, so the actual path against the chosen sky area was found and a plot of the tracks for January 2019 obtained against their sky maps using the German Space Agency's web-site at heavensabove.com. These were translated into the different projection of the sky used for the display and the information passed to the Graphics Department for inclusion in the final artwork which was then returned to us for checking. On agreement, the backdrop and the screen frame order was placed with the production company.



Proposed Backdrop From Graphics Dept.



Satellite Tracks and Orbits Added



Artwork & Frame After Production, Ready For Electronics



The Control Board Electronics



The aim of this activity is to light up the “Satellite” positions by pointing a Laser Pointer beam at sensors in location spots as with the "Star Trekking" Activity, so the control electronics could be used as before. The circuit chosen is a simple Set / Reset Latch logic circuit, four of which are in each package (CD4044BE), whilst interfacing to and from the backdrop targets is made using small high gain buffer amplifier circuits (known as Darlington Drivers) in another integrated circuit (ULN2804A) where 8 of these could provide input buffering to the four Set inputs and outputs buffering for the four Latches. A simple external common button circuit was added to the control boards which connects to all the Latch Reset inputs so that the display can be cleared of any previous activity attempts for someone else to try. However, constructing more control boards was time consuming so it was decided to reduce the channel count per board from 16 to 8 and make the control boards into printed circuits for quick assembly in the future. A suggestion to use a new service, "Fritzing", a free application software intended to help amateur constructors produce reasonably priced low volume p.c.b's, was explored. Notes on our experience with "Fritzing" are appended at the bottom of this page. To easily check the Control Board function, a small simple tester was wired up which could plug into the backdrop connector sockets, and simulated each circuit detector and LED output. When the Board is reset, all four LEDs were extinguished, and they could be activated by a momentary short between the sensor terminals adjacent to them in each of 4 circuits to check the Board operation.



Basic Outline Of One Channel



8-channel Control Board Schematic



8-channel Control Board PCB Traces



Contro;l Board Populated Ready For Testing



Plug In Control Board Circuit Operation Tester



Control Board Tester Circuit



Track Animation Electronics



There are four Low Orbit Satellites which Goonhilly originally worked to, Telstar 1&2, and Relay 1&2, all of which are shown on the backdrop. After these, Geostationary Satellites were used, all of which are placed along the blue Equatorial Plane on the backdrop. To differentiate them, it was decided to make the low orbit track activate when the appropriate satellite was selected, so a small Track Activation circuit was added behind the satellite to initiate a marching pattern along the track once the circuit was activated by the main Control Board. The basis for this circuit was two cycling 8-bit shift registers rotating a pattern which is loaded into it serially at startup, and all the parallel outputs drive directly to a string of LEDs along the track. A prototype circuit proved the concept, so again we used "Fritzing" to get PCB's made for ease in final construction. Additionally, a simple Tester for the PCB's was also made for quickly checking the Track Activation boards. This consisted of 16 small LEDs and their series resistors placed on a small bit of PCB and connected to a Plug for the Track Activation Board socket.


Two other small boards were also made to each represent the main longitudinal positions of a range of Intelsat Satellites positioned there through the years of operation. It was decided that clusters of three LEDs at each position of the Indian Ocean Region (IOR) and the Atlantic Ocean Region (AOR) as the two regions worked by Goonhilly, connecting to 79 countries over 2/3rds of the Earth's surface, would be enough of a representation.



Track Animation Circuit Schematic



Final Track Animation PCB Layout



Track Animation Board Completed



Track Animation Tester



INTELSAT IOR Satellite Cluster Card



INTELSAT AOR Satellite Cluster Card



The Team



Because of delays in getting some of the PCB's back from the manufacturer caused by a production problem, it became necessary to get additional members of the Society to help with making up the electronics on the boards and test them, and also to create the LED track chains and other connections to fit into the backdrop, as it was, by then, very close to the Schools event it was needed for. Tony, Robin, Simon, and Des had to attend an unplanned day before the event to complete and test the final production as a result, and the laboratory became a hive of activity. Fortunately we had decided to create simple Testers that could be plugged in to the boards to quickly check their functions, so time was better used for the installation and it was ready for transfer to the Event area by the end of the day



Tony Assembling A Control Board



Simon Assembling An Animation Board



Des Assembling An Animation Board



Robin Fitting A LED Chain To A Satellite Track



No Comments About The Wiring Yet, Please!



Testing The Front Display



Notes About "Fritzing" Software



This application contains large add-to component libraries, with the capability of creating a circuit diagram, which can test for, and indicate, connection errors as you work. When you are happy with the circuit and there are no errors reported, you can select an automatic translation into a normally double-sided p.c.b. layout. This doesn't always work, though, and in complex circuits can leave many traces as "don't know" dotted connections between where you need to connect, which must then be routed manually. Auto-placement of the components can be haphazard, so we found it best to lay out the components ourselves to make circuit tracing on the final p.c.b. easier once assembled. A great tool in "Fritzing" is the fact in both circuit and p.c.b. modes, if a trace is selected, then it is highlighted along its length so you can check if all intended component connections are made, and there are no breaks in the trace which could otherwise be taken by the automatic checkers as two perfectly OK traces. Once all the checks are satisfied, the completed coding can be directly sent via the Internet from the Application to a company in Germany by filling out an integral order form and authorising payment in advance, and the produced p.c.b's will be delivered in a week for assembly and testing. It is possible to send the code to a local company if so desired, although it is hardly worth it.


One note of caution in "Fritzing" is that not all components are available in their, and available user's, libraries, so you may have to create the relevant parts yourselves. This can be very complex. So while I concentrated on getting the rest of the circuits entered, I recruited another GHS member, Antony, to have a look at some new connectors we had decided on, and he successfully followed through the instructions and produced the Connector 1,2,& 3 objects on the Control Board as needed. All looked OK, but when the boards finally arrived back, consternation as there were no through-plated holes for the connector pins. Apparently, and not very clear in the instruction, through-plated holes must be defined a certain way, but the editing software recommended, "Inkscape" does not use a circular tool to draw circles, only ellipses. Even though the option actually makes a circle, this is not the acceptable object for the routing software in "Fritzing". Assembly of the production boards this time had to be by drilling all the holes out and ensuring the traces each side were properly soldered to the through pins of the connectors. Apparently, the best way to do this is to copy an existing component's through-hole to get the correct coding.