A Redesign of the DRO-350/DPU-550 Case

Let me begin by stating that the comments and analysis contained herein are in noway a critism of the original design for the DRO-350 case. At the time that case was designed, the DPU-550 was not even a dream. But my experience with the DPU-550 has convinced be that a redesign of the DRO-350/DPU-550 case is in order.

The construction of the DRO-350/DPU-550 differs from a "Plain Jane" DRO-350 in several ways.

First, there can be up to four Aux/Tach/Edge inputs. The DRO-350 has only one. Next, although not a change, the DB-9 connector, although changing from a connector for the JDM programmer to a connector for a true RS-232 connection, still occupies "real estate" on the case.

We then add the capability to increase the number of possible scale (Mini-Din) inputs from 3 to 5. Then we have added the openings for the USB connector and the programming switch. And of course, we have to have the power jack.

The additional openings unto themselves would not be a particular problem if we still had all the room that is available inside the "Plain Jane" DRO-350 case. But the DPU-550 occupies space inside the case and restricts the potential locations for the additional openings. Plus, the position of the USB and Programming Switch openings are dictated by the location of these components on the DPU-550.

The instructions on the ShumaTech web site assume that a DPU-550 is being added to an existing DRO-350, and that the original DRO-350 case will be retained. If shows the locations for the USB and Programming Switch openings, but makes no suggestions for the expansion allowed by a DPU-550 Full daughter board.

I have taken the approach that rather than dealing with an upgrade to an existing DRO-350, we are building a DRO-350/DPU-550 from the ground up. Variations of my design can be used to expand the capabilities of the original DRO-350 case when upgrading to a DPU-550.

The primary driving force behind my belief that a redesign was in order, was the crowding of the scale input cables that occurs beneath the DPU-550 daughter board. Because of the location and orientation of the X, Y and Z input connectors on the DRO-350 processor board, coupled with the placement of the openings for the Mini-Din connectors along the bottom edge of the rear of the case, it is difficult to route the scale cables away from the area of the LED displays. Although there has been debate on whether moving the scale cables away from the LED displays and the associated circuitry, reduces jitter, there has been no evidence that routing the scale cables away from that area presents any problems in the operation of the DRO-350 or DRO-350/DPU-550. So my design errs on the side of caution.

The photo above shows the new design with three scale connector openings located over the keypad area of the DRO-350 processor board and two Aux/Tach/Edge connector openings along the top rear of the case. This design allows for easier routing of the scale cables away from display area of the DRO-350 processor board and the higher frequency (40 mhz) ARM7 MPU on the DPU-550 daughter board.  The power receptacle remains in approximately the same location.  Also seen are the openings for the USB connector and the programming switch.

 

The next photo shows the rear case cover from the inside. Visible in this photo are the pilot holes and reliefs milled for the purpose of expanding the number of scales and/or Aux/Tach/Edge connectors. These additional openings can be created with a simple drill and utility knife. Cases delivered without the RS-232 DB-9 opening also have this opening outlined and piloted.

(Please excuse the lack of clarity in these photos.)

The Aux/Tach/Edge connectors delivered with the Wildhorse Innovations kits are slightly different from those specified in the ShumaTech BOM. These connectors (both Wildhorse's and ShumaTech's) are merely 10mm Stereo Jacks.  Their jacks have the nut on the inside so the wires must be soldered with the assembly in the case.  Ours (Wildhorse) have the nuts on the outside so the soldering can be done before installing into the case.

The threaded "neck" of the Wildhorse jacks are slightly short for the thickness of the case.  They can be installed, but the number of threads engaged by the nut is insufficient.  The nut can be tightened down with pliers, compressing into the plastic.

Our cases have a relief milled into the inside of the cover for the stereo jacks, allowing more threads to be exposed.  These reliefs are also milled for the "piloted" areas provided for additional Aux/Edge/Tach openings.

An additional difference is that our jacks have a slightly smaller neck than the ones specified in the BOM.  Ours require a  0.250" opening.  The ones called for in the BOM require using an "O" letter size drill.

Some additional dimensions:
Bolt holes for Mini-Din connectors and RS-232 jack - 0.125".
Openings for Mini-Din connectors - 0.500"

If you are install the RS-232 (DB-9) receptacle, using the pilot hole in the center of the DB-9 outline, drill a #10 or 25/64 hole.  Then use an exacto knife, following the outline milled into the case, to create the final shape.

As usual, all coments are welcome.  We hope our new case design meets with your approval.

New Shipping Policies for Wildhorse Innovations

Since our inception in April of this year, Wildhorse Innovations has offered flat rate shipping on all orders.  However, as we expand our product offerings to include more and more items of general interest to the home machinist, flat rate shipping has become a money losing proposition.  (We can't ship a 50 lb. milling vise for $7.00.)

All of the shipping calculation programs available to us fail to take into account unusual circumstances.  As an example, to ship 40 lbs. of cutting tools will normally cost over $25.00.  But 40 lbs. of cutting tools will quite often fit into a Priority Mail Medium Flat Rate Box which can be shipped for under $10.00.

We wanted a system that will offer the lowest possible shipping cost to our customers.

A recent addition to our online catalog is a variation of "Per Item Shipping".  Each  item has two shipping costs assigned to it, a "1st Item" cost and an "Additional Items" cost.  These costs are listed on the item description page.

Here's where we differ from most other companies.

When computing the shipping charges we take the "1st Item" shipping cost for the heaviest (most expensive to ship) item.  This "1st Item" cost becomes the base for shipping charges.

For every other item in your order we add the "Additional Items" cost for that item, even if you are ordering only one of that item.  To that total we add a $2.50 "Handling Charge".  However, as you will soon see, this is a handling charge in name only.

We use the $2.50 handling charge to compensate for orders that contain only very small items and may be shipped by First Class Mail.  These small items will list very low shipping costs (sometimes under $1.00).  Shipping for these small items will normally never exceed $5.00.

Now for the good news.  You will always be charged the lower of the actual shipping costs, or the computed shipping costs.  So if you are charged $8.00 shipping on your online order and we can ship your items in a Small Flat Rate Priority Mail Box for $4.80, you will receive a refund of $3.20.

Likewise, if you are charged $8.00 shipping in your online order and we need to use a Medium Flat Rate Priority Mail Box (which ships for $9.80), you will be charged only the $8.00 shown on your order.

To repeat; You will never be charged more than is shown on your online order.  And if the actual shipping charges are less than the amount shown on your order, you will receive a refund of the difference.

Please email us at info@wildhorse-innovations dot com with questions or comments.

Hemostats - The Third Hand You Always Need When Assembling Electronics

I've used hemostats for years for a variety of tasks. One of the most common uses has been to hold components in place for soldering when assembling an electronic kit.

When I found these compact, well made and inexpensive hemostats, I decided to add them to our Wildhorse Innovations store and write this blog about their use.

For those of you not familiar with hemostats, they were first invented for use as a surgical tool.  They are the pliers like surgical tool that doctors use to, among other things, clamp off blood vessels during surgery.  They are made in many sizes with a variety of jaw shapes.

The handles of the hemostat have a set of interlocking fingers designed so that the hemostat automatically locks in a ratchet like manner as they are closed.  The fingers have several ratchet grooves that allow the hemostat to apply varying amounts of grip as they are closed.  To release the hemostat, apply pressure to the handles (as if you were closing them) and move the handles slightly apart so as to release the ratcheting fingers.

When assembling electronic kits I find the hemostat most useful for holding components with stiff legs (such as a voltage regulator in a TO-220 package).  They are especially useful for holding pin headers that not only have stiff legs but also very short legs.  Depending upon the circumstances I may use them to hold DIP ICs in place for soldering.  I almost never use them to hold components with long, flexible legs such as resistors.  It is much easier and quicker to just spread the legs after inserting the component through the holes.

Hemostats are not a "must have" for the electronic enthusiast. Some people advocate using the "heat and plunge" method of inserting items such as headers. Using this method, you cover one of the holes with solder, then while holding your soldering iron in place to maintain the solder in a molten state, you quickly insert the header into place. I've used that method at times, but after many burned finger tips, I decided that hemostats were the way to go, no matter what the cost. The low price of these hemostats take cost out of the picture.

Speaking of pictures, I have inserted some below to show the use of hemostats. They are of my usual non-professional quality, but they get the point across.

The first two pictures show hemostats being used to hold a TO-220 voltage regulator in place for soldering. Pin headers and ICs are shown later in this blog, but the procedure is about the same for all devices.

The top picture shows a side view of the voltage regulator held in place by the hemostats.  The voltage regulator is a little slanted but we will correct that later. The  bottom picture shows the view from the bottom of the board.

From here on, the procedure is quite simple.  Solder ONE leg of the voltage regulator.  While the solder is still molten you can use the hemostats to adjust the placement of the component.  As an alternative, you can remove the hemostats and reheat the joint while adjusting the placement with your free hand.  Now solder the 2nd and 3rd pins.  After you have finished with the last two pins, go back and reflow the original pin.  Since you were adjusting the position of the component while this joint was molten, there is always the chance of getting a cold solder joint.  Reflowing after the component is solidly in place eliminates this possibility.

The next two pictures show the same procedure, this time used on a pin header.  One big advantage the hemostats have in this situation is that the bottom if the pin header is designed to seat flush against the surface of the board.  Letting the hemostat hang off the side of the board pulls the pin header toward the surface of the board.  With a little practice you can hve the pin header seated properly the first tme, everytime.

But don't forget to reflow the first joint soldered.  Even with the pin header securely seated, there is always the chance of a slight bit of movement causing a cold solder joint.

The next two pictures show hemostats used to secure an IC for soldering.   The procedure is slightly different for this type of component.  With the hemostat holding the IC in place, solder two diagonal corner pins.  The remove the hemostat and while pressing the IC towards the surface of the board with one hand, reheat the two solder joints and allow the IC to seat firmly against the surface of the board.  Solder the balance of the pins and reflow the first two.

 

 

OK, that's the end of today's lecture.  I hope you've paid attention.  You never know when there might be a pop quiz.

One last thing.  Hemostats make great heat sinks when you need to isolate a component from the heat of soldering.  Today's components are pretty tough when it comes to soldering, but there once were components that were very sensitive to heat and could easily be ruined during the process of soldering.

As always, you comments and opinions are welcome.