This is an excellent alternative to pricey brand name racks. I don't have some of the original stuff that I recycled to make the item, so I'll do my best. (I've only just discoverd Instructables, my projects are all old, and go as far back as 2000.)
My 'dashboard' includes (From Left to right) GPS, speed/ odometer, and bell (required by law)
Step 1: View of the Rack and Ingredients
I recycled the Fastex quick release buckle and bracket from an old Blackburn seatbag; the zipper had blown, so after a lot of thought, I dissected it.
From it I kept the quick release buckle and the square of plastic it was rivetted to. I hope these pictures help.
Quick release buckle (Maybe sold as a unit somewhere...)
inner tube shims
allen key set
small nuts and bolts
Step 2: Attach Plastic Tray to Female Portion of Quick Release Buckle.
I used 4 small bolts to secure the plastc tray to the female portion of the buckle. In the photo, you can see the original plastic bottom of the bike bag attached to the buckle; also the 4 nuts and bolts are visible, as well as the inner tube retaining bands. Ensure the nuts are on the exterior, so the GPS doesn't get scratched. Note that the bottom left nut is a plastic lined lock nut. These are preferable, as once on, they will not loosen off.
Step 3: The Top 1/2
Here's a pic of the tray; I found it in a scrap pile at work a couple of years ago, and it fits the Garmin GPS76 family like a glove. Hooray for scrap!! Note the positioning of bolt heads; locknuts, the nuts with a plastic liner, are best; when you thread them on, a lockwasher isn't required, because the plastic sleeve in the nut grips the bolt tightly. They are awesome.
Step 4: Securing Male Half of Quick Release Buckle to Handlebars
This is the piece that was originally attached to my seat post; the bag would lock onto it quickly and easily; I'm glad I recycled it.
I first put 2 hoseclamps on, with inner tube shims, and tightened them until they stopped wobbling all over. I then took the male portion, and inserted it into the hoseclamps. As can be seen, the hoseclamps hold the two-piece unit on the handle bars; the allen nuts were originally used to hold the male buckle to the rails under the bicycle seat, and now are secured to the hoseclamps. Copious inner tube shim was used beneathe the hoseclamps, both between handlebar and hoselamp, as well as between hoseclamp and male buckle.
Step 5: Final View
A last glimpse of the hoseclamp / buckle attachment. Now, the female portion attache to the tray slides and locks on to the male portion of the Fastex buckle. Muy bueno, eh?
I wish I could have documented this procedure prior to discovering Instructables. As mentioned, maybe the quick release buckle can be found as a unit? I hope this helps and inspires creation!!