Astronomy in Focus

Power to the Masses!

Sunday, 10 April 2011 20:51

So as a budding astro-imager, I have collected a fair bit of gear in the past couple of years.  And almost all of it requires power.  Worst of all, they all use different batteries and voltages.  And none of these batteries like the cold.  Especially my cameras.

After much hemming and hawing on this, I decided I needed a system that would permit me to run all of my gear from a relatively power source that was portable.  Specifically, my power distribution box, which I already cart with me anytime I do some observing or imaging.

Much of the inspiration for this project comes from two blogs.  The second one I can't find the bookmark for right now, but provided the basis for the use of a Texas Instruments switching regulator.  I'll try to find the blog, but no promises.

Regardless this second blog, provided some insight into the use and availability of a regulator which was a direct shoe-in for the one my friend Colin designed for me and just didn't seem to cut it.

Regardless, the project would not have been possible (or financially viable) without the help of The Roaming Drone.  Specifically, this post, where the specific Hirose connector used on the Pentax K10D and Pentax K20D cameras is identified for purchase from digikey.ca.

Further, this image was also extraordinarily helpful, as it describes the exact wiring of the afore-mentioned Hirose connector.

So, now that the temperatures are finally above zero, and I no longer truly need these adapters and connectors, I seized the opportunity presented by an extremely wet and rainy weekend to sit down with some wiring schematics, the parts I recently purchased and my soldering iron.  The pictures that follow, are a documentary of the weekend's efforts.

Do keep in mind, that I haven't actually powered up either my K10D or my K20D with these assembled products.  I've simply run out of time this weekend, and I'd really appreciate the help of my friend Colin in testing this before I potentially sacrifice a perfectly good camera.

 

This first picture shows the size of the Texas Instruments PTN78060WAH DC-DC power supply.  The entire bottom side of this assembly is riddled with surface mount devices.  In this package, the assembly is pretty easy to work with.

 

This pictures shows the front/top of the fully assembled power supply.  Keep the first picture above in mind to realize how small this entire circuit truly is.  Unfortunately, the holes of the breadboard were simply too small for the regulator and potentiometer, so some indiscriminate drilling was required.  GO Makita!

 

This pictures shows the back/bottom of the fully assembled power supply.  The red/black wires on the left are the 12VDC inputs, wheras the green/black wires on the right represent the regulated output.   You can see along the middle that beyond the regulator assembly requiring the holes in the breadboard to be bored out, that some of the pins, aren't even aligned "on-center" with the holes, requiring some interesting use of my drill to "oblong-out" some holes.

 

Here's the "enclosed" circuit board in all it's glory!  Using a 5.1Kohm resistor and a 500ohm potentiometer. This resistor and potentiometer are used to dial-in the resistance between pins 4 and 7 to exactly 5.34Kohms, which provides a perfect 8.3V output.  Being variable, I can still adjust this resistance to anywhere between 5.1Kohm and 5.6Kohm, should I need to accomodate for voltage drop across the "output" lines over the length of the cable to the cameras.

 

Now that the DC-DC power supply is done, time to start assembling the Hirose connector.  Here we see the connector (with positive/negative markers added by me) soldered together.

 

Here we see a little bit of insulation added to keep the connectors from shorting out against the metal shield.  Isn't electrical tape just awesome?

 

This photo is tough to see, but the integrated metal shield/harness/clip is attached to the black connector.

 

Here we can see the "jacket" partially slid over the connector assembly.  This was probably the toughest part, since this connector appears to be built with some very tight tolerances. Add to that the relatively thick cable I used, combined with the addition of the "insulator" I added, and you can only imagine the force needed to get this jacket over the main body of the cable/connector assembly.

 

Here we see the connector fully jacketed.  Looks just like the original Pentax Cable.  Or is it?

 

And here we get an extreme closeup.

 

One final test to make sure everything fits together on the K10D.

 

Finally, two K10D/K20D connector are assembled on pigtails.  The ends of the pigtails will be dramatically shortened once I get the proper 18ga SJOW (or possibly 20ga) cabe I'll be using to cable the cameras to the power distribution box.

 

And here we see both sets of finished assemblies! (2 sets of connectors and 2 sets power supplies).  One each for my K10D and K20D.

 

Sometime this week when the power-distribution box connectors come in, I'll hardwire the DC-DC powersupplies into my distribution box, and give the power suppiles their first end-to-end test.  When I (finally) pick up the 18ga SJOW wire (which is flexible at -25c), I'll be able to get this all wired from end-to-end, including the power modifications I've made to my Atlas EQ-G mount, which are all waiting for the same sub-zero-flexible cable.

 

Clear Skies!