Poorman's Space Program

The BalloonSat Extreme

Part 2. When "One Experiment-One BalloonSat" Just Isn't Enough

L. Paul Verhage

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I hope some of you were able to make the BalloonSat Extreme printed circuit board (PCB) described in last month's The Citizen Scientist. After making your PCB, you'll solder components to it in the following order (we're going from the lowest lying to the tallest components). Use the next image to help you locate the proper location for the components.

Figure 4. Parts placement diagram for the BalloonSat Extreme printed circuit board.

Six jumper wires (use cut resistor leads)

Four 1k-ohm resistors

Three 1N4001 diodes

For the first three sets of components, bend their leads to the proper spacing first and then insert them into the PCB. It's less stressful for the components if you do it this way rather than bending the leads as you solder them to the PCB.

Cut and strip 16 pieces of wire for the flight computer cabling. A length of 6-8 inches ought to be long enough unless you're making a BalloonSat of Unusual Size (BOUS).

The battery packs have their own leads, and you won't have to prep them--just solder them to the PCB. The positive lead (red) is soldered to the wire marked +V in the diagram above and the negative lead (black) is soldered to the wire marked G.

The wires in the cabling pass through the large holes at the edges of the PCB (from the underside) and are then soldered to the next set of holes. The large outer holes provide a strain relief for the cabling; this makes is much less likely they will break off from use. The following diagram should make this clear.

Figure 5. A side view of the PCB illustrating how the wires in the cabling are strain relieved. Only strip wires at their ends; do not pass stripped wire through the larger, outer holes.

Next, solder the switches, LEDs, and 1/8 inch mono receptacle to the ends of their respective wires.

Before soldering switches, the receptacle, and the LEDs, slide a length of heat shrink tubing over the wire. Then, after soldering the component, slide the heat shrink over the connection and shrink it to protect the bare lead from shorting against an exposed lead or contact.

Note: The orientation of the switches and the mono receptacle is irrelevant. However, the LEDs must be soldered in the proper orientation or they will not function (this doesn't prevent the rest of the flight computer from still working). The cathode connects to ground; its wire is labeled with a C. The anode of the LED connects to +5 volts in this flight computer; its wire is labeled with an A. The cathode lead is the one on the side of the LED lens that is flat. See the next illustration for more detail.

Figure 6. Normally, the short lead is the cathode and the long lead is the anode. However, don't bet your life on it. If the LEDs are surplus, they might be modified.

The proper terminations for the camera ports depend on how you cable your cameras. I recommend using Dean's micro plugs (available in many hobby stores).

Six capacitors are required. Some of these are polarized – look at the placement diagram above for their proper orientation.

Two IC sockets are used. These are not polarized, but they do indicate the proper orientation of the ICs, and that is critical. So solder them in the orientation shown in the illustration above.

Three relays

Two receptacles

One header

Testing

Don't plug the BS2pe in and flip the switch just yet. Although it should be difficult to damage the ICs, it is possible if something is not soldered properly. So perform these tests before going any further:

1. Shorts

Use a multimeter to check for continuity between power and ground in the battery packs (with the power switches in the closed position). There should be no continuity.

Check for continuity between the +5V and Ground holes in the receptacles. Again, there should be no continuity.

The previous two tests looks for shorts between power and ground before and after the voltage regulator.

2. Voltage

Now insert the batteries, flip the power switch, and measure voltage with the multimeter. There should be five volts (give or take 0.25 volts) between pins 4 and 21 of the BS2pe socket.

Do the same with the servo battery pack and measure the voltage between the power and ground pins of the servo header. There should be 4.5 volts or 6 volts, depending on your battery pack.

3. Communications

Switch off the power and then insert the BS2pe and the MAX186. Start the BASIC Stamp Editor and type this program:

DEBUG “Test”

Download the program and you will get a pop-up screen displaying this text: Test

Now connect a 10k resistor between the ground and signal of the Analog Port #1. Then type and download the following program in the BASIC Stamp Editor:

SHIFTOUT 2,0,1,[$8C ]

SHIFTIN 2,0,2,[W0\12]

DEBUG DEC W0

The debug screen will pop-up and display a value of about 0 if the BS2pe can communicate with the MAX186 properly.

Finishing Up

I recommend painting red and green dots on the PCB to indicate the power and ground columns in the Analog, Servo, and Digital Ports. You can see the ones I added to my BalloonSat Extreme in the close up photograph at the beginning of last month's column.

Figure 7. A complete BalloonSat Extreme in all its glory.

The Commit Pin is a 1/8 inch mono jack with a short loop of wire soldered between the tip and base. Look at my previous articles on making the Commit Pin for the other BalloonSat fight computers. For greater durability, be sure to squirt some hot glue around the soldered connections and into the jack housing after screwing it on. Then tie a strip of brightly colored cloth to the wire loop protruding from the back of the Commit Pin to remind you to remove it before the BalloonSat lifts off (or you can use the flag to remind you that you forgot to start your BalloonSat as you watch it rise out of your reach).

There are a lot of cables hanging off the BalloonSat Extreme. Follow the same procedure I outlined in early articles on BalloonSat flight computers to create a control panel from a sheet of 30 mil plastic. However, with the BalloonSat Extreme, the control panel must have holes for the following:

Two toggle switches

Two LEDs

One 1/8 inch mono receptacle

A good design, one where the controls are meaningful, places each LED next to its toggle switch. Position the mono receptacle where the flag hanging off the Commit Pin doesn't hang over the toggle switches or LEDs.

Add plastic (or even metal) spacers between the wings of the DB-9 connectors and the BalloonSat Extreme PCB before you bolt the connector to the PCB (don't rely solely on the soldered pins to hold the DB-9s to the PCB). The #2-56 hardware is the perfect diameter for this. You can't go much smaller than 3/16 inch for the diameter of the spacer tubes or they may slip through the mounting holes in the DB-9 connector's wings.

Conclusion

What can't you do with the BalloonSat Extreme? Well, for one thing, it doesn't do floating point math. That's all right since you'll do that in a spreadsheet after downloading the data. It also doesn't transmit its data to the ground. That actually makes using the BalloonSat Extreme easier for students, since they don't have to earn an amateur radio license to test and use it. However, the BalloonSat Extreme combined with an APRS tracker creates a complete near spacecraft for anyone wanting to go that route.

I'll post an example of flight code for the BalloonSat Extreme on my web page (nearsys.com) under Catalog. Right now, the BalloonSat Extreme is not available as a kit. If, however, you're interested in making your own but can't make the PCB, contact me, I can shoot a copy of the PCB for you to solder for yourself for around $10 to $12. If there appears to be a large enough interest, I'll develop the BalloonSat Extreme into a kit.

Onwards and Upwards,

Your Near Space Guide

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The Citizen Scientist (07 August 2009).