Step 1: Materials
1 36" length of 1" electrical conduit
4 3/8" quick links
2 3/8" S-hooks
2 3/8" x 4" eye bolts with nuts
2 3/8" x 4 1/2" eye bolts with screw threads
2 3/8" washers
3/8" and 5/16" drill bits
Make sure that the hardware you buy has a load rating appropriate for the amount of weight you'll be putting on the bar. The lowest rated part I used was the eye bolts, and they were rated for 160 lbs. With two of them, you should be covered under most reasonable use. All of the measurements and hardware sizes are adjustable - I just bought the heftiest looking parts I could find in the store. For the bar itself, I chose aluminum so that I could drill easily through it - at this length it was clearly strong enough to support weight without bending.
Step 2: Drill holes, add hardware
Drill a 3/8" hole all the way through the pipe at each end. It helps to drill one or more pilot holes to gradually get to the right size, especially if you don't have a drill press. With a hand drill, this was a little tricky because the bit would tend to catch on the hole edges just as it went through and get stuck - going very gradually with the drill running at a high speed helped that.
Insert the eye bolts into the holes and thread on a washer and a nut on each end. Tighten these down firmly with a wrench or pliers. Next, add a quick link to each eye bolt. Set the whole thing aside for now.
Step 3: Drill ceiling holes
Once you've figured out where the joists are, mark your holes about 34" apart. Lining them up so the bar is parallel with one joist will make it so you can mount whatever length bar you'd like, rather than using multiples of 16". Drill straight up with your 5/16" bit for both holes. It's a good idea to make a pilot hole here too, to verify that you've hit the joist and to make sure you're straight.
Screw the eyes into the holes - it should be fairly hard to get them in, that way you'll know they're really secure. You can stick a strong screwdriver through the eye and use that to get leverage to twist them in.
Step 4: Put it all together
The bar is free to move a little, but I didn't find that this affected the pull-ups very much. If anything, it would make it slightly harder, but we're not going to complain about a hard workout, are we? You can easily stick a band on for assisted pullups, or use the bar as a mounting point for gymnastics rings. (I wouldn't do any real gymnastics on them though with this mount- just strength training stuff.)
Have a good workout!