Comments on the DRO-350

For over a year, Scott Shumate has displayed the following doomsday comment regarding the DRO-350 on his web site (Shumatech.com).

"WARNING!!! The DRO-350 is an old design that uses obsolete parts. The DRO-350 has a number of problems including scale jitter, rounding errors, and axes that won't display. These problems will not be fixed and all future development activity will concentrate on the DPU-550 and DRO-550. The DRO-550 completely solves all of these problems and adds a huge list of new features."

With over 6 years to solve these problems (2003-2009) one might wonder why, with basically the same circuitry, the DRO-550 is providing a miraculous solution to this problems.

At Wildhorse Innovations we have had many inquiries regarding the dire warnings and extreme statements contained in that post. This blog post is an attempt to bring to light the true status and nature of the the DRO-350. Whenever opinions are expressed in this post, they will be clearly labeled as such. However, even the opinions are not lacking in facts. They are based upon over 40 years of experience in the field of electronics and an earnest effort has been made to exclude personal prejudices from the opinions stated.

"The DRO-350 is an old design": True. The DRO-350 was originally designed around 2003 and not much has changed in the meantime. It was, and is, a stable well designed DRO for use with what are commonly referred to as "Chinese" scales. The DRO-350 is so well designed that the most critical portions of the design are DIRECTLY imported into the DRO-550 (the scale interfaces and the AUX/TACH interfaces). A side by side comparison of the schematics of the DRO-350 and the DRO-550 will show that the primary differences occur in the power supply section (providing 3.3vdc for the MPU) and the various additional interfaces added. It might be noted that many of the "New" interfaces are non-functional because no software has been developed for them.


"WARNING!!! The DRO-350 is an old design that uses obsolete parts.": Partly True. To paraphrase the infamous words of President Bill Clinton, "It depends on the meaning of obselete.". Have you ever gone to an auto parts store with a part number only to discover that the part has been superseded by a new part? Is your old part "number" obselete? Yes. Is there a new part that bolts in place, performs the same function and allows you car to function in exactly the same manner as with the "old" part? Yes.

So it is with electronics. Manufacturers will change part numbers for a number of reasons. Over the past dozen or so years, EPA regulations and the ECM's ROHS standards have forced manufacturers to redesign parts to eliminate what have been deemed hazardous substances. Some manufacturers have merely made minor changes to parts to meet the new regulations and stuck an additional prefix or suffix on the part number. Others have taken the opportunity to increase the overall functionality of the part and relabeled the part with a totally new part number.

So what is the bottom line for the DRO-350. ALL PARTS FOR THE DRO-350 ARE CURRENTLY IN PRODUCTION. Have part numbers changed? Yes. But we at Wildhorse Innovations continue to provide our customers with all necessary cross-references so you can readily identify any parts on which the identifying numbers have changed.

"The DRO-350 has a number of problems including scale jitter": This issue has been a thorn in the side of "Chinese" scales since day one. Little, if any of the problem can be solved in the design of the DRO-350 (or the DRO-550) or the software. The problem lies in several areas.

First, the "Chinese" scales are not really designed to be used with a remote head (the DRO-350 or DRO-550). They are not designed to use an external power supply. They are designed to receive their power from the 1.5vdc "button" batteries that are inserted into them.

Second, the "Chinese" scales determine "position" by measuring the varying capacitance that is present between the scale readout and the rail as the readout moves along the scale.

These conditions make up the bulk of the jitter issue.

When we provide the power for the scale from an "outside" source (such as the DRO-350), we are sending this power through a rather lengthy cable which is subject to all manner of EMF influences. Couple that with the fact that the power transmitted through the cable is VERY low (1.5vdc at a few milliamps) and you have a perfect formula for disturbing influences from outside EMF. As mentioned above, the circuitry in the scale readout is "expecting" to receive rather stable power from a battery mounted just a fraction of an inch away. The circuitry is not designed to cope with the possibility of fluctuating supply voltages.

Another influence on the jitter issue is that the "Chinese" scales determine position by measuring the capacitance between the readout (sliding portion of the scale) and the scale rail. Obviously anything that influences that capacitance will alter the scale reading and introduce jitter. These influences can include improper grounding of the scales (or creating ground loops), introducing vibration into the scale as the machine is running or ANY source of EMF acting upon the scale itself or the cables connecting the scale to the DRO head.

There have been many "solutions" to the jitter issue. (Any belief that the jitter issue was solved with the DRO-550 is quickly disspelled by a quick perusal of the ShumaTech forum.) Some have involved leaving the battery in the scale. Some involve installing capacitors in the battery compartment of the scale. At Wildhorse Innovations we have found the following steps solve 99% of the jitter problem.

1. Keep cable runs as short as possible.
2. Route the cables inside the DRO-350 case in areas away from the display section of the PCB.
3. If using shielded cable, ground the shield ONLY at the scale end of the cable.
4. Route cables so as to avoid EMF interference. NEVER run scale cables parallel to high voltage cables. Also, NEVER run scale cables parallel to stepper motor cables.
5. Most scale head bodies are connected to the negative side of the power supply. When mounting the scales, insulate the bodies from the machine. Failure to properly insulate the scale head bodies can result in ground loops.
6. Mount the scales to the machine so as to minimize the transmission of vibration from the machine to the scale.

"rounding errors": True. You carry your calculations past 5-6 decimal points, the DRO-350 has rounding problems. So you guys that are working with tolerances in the 0.00001" range probably need a different DRO.

"axes that won't display": To be honest, we at Wildhorse Innovations have never seen this problem in a standard DRO-350. We have seen it in DRO-350 with DPU-550 daughter boards, but it is rare and since the DPU-550 is no longer produced, it appears to be a non-issue for the new purchaser.

"These problems will not be fixed": Easy solution Scott. Release the source of for the DRO-350 as Open-Source. Let the market place find the solutions. There is a new drop in replacement for the PIC16F MPU used in the DRO-350 (the PIC18F) that has over 3-1/2 times the memory of the PIC16F and an improved, more powerful instruction set. It costs only about $1.00 more than the PIC16F, so any increase in cost of the DRO-350 would be minimal. Additionally, since it is a literal drop in replacement, every DRO-350 in existance could be upgraded for under $15.00.

"The DRO-550 completely solves all of these problems": Sorry, but to be blunt, this is a total falsehood. I'm not saying the DRO-550 does not have it's up side, but 10 minutes on the ShumaTech forum will show that the DRO-550 has its share of problems and solutions are sometimes slow in coming. Scott has a stranglehold on the software and it almost seems that if it is not Scott's idea, it doesn't make it into the code. And after over 2 years, we have yet to reach release 1.0.

"and adds a huge list of new features.": Absolutely true! And if they are features you need/want and are willing to pay for, then there is no reason to not purchase a DRO-550 (when you can find one). The ability to mix and match different protocols is a hugh advantage for those that need it. (Did we mention that this same feature could be an upgrade to the DRO-350 if Scott were to release the source code?) And the advertized features that don't yet work will be a real plus when they go live. I'm sure target dates will be announced soon.

Now for an opinion. The DRO-550 is a throw away board. By this I mean, when something goes wrong, (borrowing from "Ghost Busters") "Who ya gonna call?". The DRO-550 is a 4 layer, surface mount board. If you look at the repair services, only the most expensive multilayer SMT boards are repaired. It's time consuming, requires special equipment and expensive to repair these types of boards. Plus, with the small number of DRO-550 boards produced, no repair house can afford to set up the "line" and train personnel to repair the small number of repairs that would come in. But when it's your board that needs repair, one is not a "small" number.

We get emails virtually every week asking about repairs for the DRO-550. The only advise we can give is "buy a new board".

This is not Scott's fault. But he could set up an exchange program to ease the pain for the customer. Yes, he will most likely junk the old board, but at least he has acknowledged the value of the customer for having purchased the DRO-550 in the first place.

BOTTOM LINE:

The DRO-350 is alive and well. It's a workable, inexpensive solution for the home machinist on a budget. Wildhorse Innovations is dedicated to supporting it for as long as possible, which we expect to be years into the future.

When used with the "Chinese" scales, it's a bargain. When used with quadrature scales, including the Igaging scales, the DRO-550 is probably a better buy, until and unless, Scott will release the source code for the DRO-350. We can then produce a low cost upgrade. It won't be a DRO-550, but it will meet the needs of many customers.

As usual your comments are welcome. Visit us at http://www.wildhorse-innovations.com.

The EAGLE has landed (well, almost)

The ShumaTech DRO-550

I need to open this blog with a full disclosure. Wildhorse Innovations (and therefore myself) cannot be considered an impartial observer where the DRO-550 is concerned. We sell, among other things, the DRO-350. The potential for the DRO-550 to have an impact on our sales is undeniable.

We always encourage reader comments and feedback. But especially in this instance we welcome you to point out any bias you find in our writings. Any reader is free to express differing opinions, and most especially, correct any factual errors found herein.

With a speed that has surprised many, the DRO-550 has been announced and advance orders for a "Power-Buy" have been submitted in, what might be called, "record time". Once the magic 100 piece mark has been reached, delivery is estimated at 4 weeks. The last information we have indicates that well over 200 orders WITH DEPOSITS have been made. That would seem to indicate that the Power-Buy is moving forward and will be a greater success than anyone had predicted. (Perhaps I shouldn't include Scott in that statement. He may have had an idea how big it would be.)

Scott has announced a cutoff date of January 20th for the Power-Buy, so there is still time to submit your order. Missing this Power-Buy could either make it necessary to wait for a future Power-Buy, or put you at the mercy of speculators who have purchased extra boards to be sold at a premium price.

Inside the DRO-550

The DRO-550 is a device comprised primarily of surface mount components. This puts it outside the normal definition of a DIY project. But this technology was necessary to load all the technology found in the DRO-550 onto a board that is the same basic size as the DRO-350. My understanding is that the reason for wanting to match the DRO-350 form is to allow current DRO-350 owners to pull out the old board and plug in the new DRO-550.

Little compromise was needed to accomplish this goal. The LED displays have been changed from Common Cathode to Common Anode so the LED displays can't be transferred from one board to the other, but I'm not sure this is a realistic process anyway. Removing the LED displays without damage is not a trivial task. Besides, the $7.50 cost for new displays really is a small price to pay when all the other improvements are considered.

The switches have also be changed, however the switch caps remain the same.

Bottom line is, in my opinion, build the DRO-550 as a completely new unit. Move your DRO-350 to a different machine or sell it on eBay.

The DRO-550 has another major change. It is now a 4 layer board (the DRO-350 is a two layer board). So between being built with surface mount components and having a 4 layer board, the DRO-550 is not only not a DIY board when it comes to construction, but it is also not a DIY board when it comes to most repairs. Ideally the repair of this type of board requires specialized equipment which is usually accompanied by pretty high shop rates (in the neighborhood of $60.00/hr).

Warranty

According to the ShumaTech web site, this board is sold without a warranty of any kind. This policy has not been clarified as it relates to DOA product. As it reads now, if you get a DOA board you're just out of luck.

There is also no statement as to whether or not post production testing is performed.

This same disclaimer of warranty also applies to the software, OpenDRO, which makes sense since almost all Open Source software is offered without warranty.

I hope that Scott is ordering a few extra boards to handle the potential DOA issue. Unless thorough post production testing is being done, the chances are reasonably high that a least one board out of the several hundred that are going to be produced will have problems "out of the box".

Making it work

The DRO-550 board is just one component in a list of components needed to make a working DRO.

The board contains the surface mount components, but a collection of through hole components is also needed. These through hole components are available as an extra cost item (at a very good price) when you purchase your DRO-550 board. I would recommend that unless there is something you want that is not found in the standard through hole component kit (such as green LED displays) you take advantage of the Power-Buy pricing for these items also.

As an aside, the switches that are contained in the through hole kit, are not through hole devices. I suspect the cost of having them placed on the board using automated methods would have raised the cost of the board disproportionately, so Scott is offering them for manual mounting with the through hole components.

Next you need some internal cables. These cables connect the headers on the board to the back of the plastic case. Which cables you need will vary with how you configure your DRO-550, but at the very least you will need a couple of internal scale cables and an internal power cable. Wildhorse offers these individually, or in kits for the most common configurations. Technically you can make your own internal cables, but I don't recommend it. Getting a reliable connection to the MTA connectors is a real pain without the proper tooling. You can buy a $10.00 or so "manual" tool, but I've used one and not only is it a pain, it's a real crap shot as to whether you will get a good connection.

Now it's time for the case. The case of choice is the Hammond 1599HBK. This is a black, fire resistant case that will stand the abuse heaped upon many components in machine shops. Again Wildhorse offers this item, either as a semi-custom case machined specifically for the DRO-550, or as on off the shelf item which you machine yourself.

Another quick side note. With the DRO-350 and the DRO-350/DPU-550 combination, the case could be machined with just two "operations", one operation to machine the front and one to machine the back. But the DRO-550 has the USB port on the end of the board and thus requires a third operation. This adds time to the machining process and thus adds to the cost of the machined case. This is reflected in the price of the case on our web site.

Next you will want a "faceplate" or "overlay". These are identical to those used on the DRO-350. As always, those offered by Wildhorse come with pre-applied adhesive eliminating the messy "spray adhesive" technique.

You can't operate all of this without a power source. Wildhorse offers the standard 9vdc 1.2amp power source that has been used for years on the DRO-350. This power supply is ample for all but the most demanding operation. If you're going to be running five glass scales, you might want to run the numbers using Scott's formulas as found in the DRO-550 hardware manual. Chances are you will require a higher amperage.

And the last two items are what the DRO is all about, the scales (and the cables that connect them to the DRO-550). The DRO-550 is a very flexible unit and will work with just about any scale on the market. The "Chinese" scales are generally the most economical for smaller installations. But when you start to look at equipping a BridgePort with a 42" table, the gap closes.

Each of these areas will be discussed in more detail in future blogs. Hopefully the information contained here-in will be enough to get you started with the planning for your personal installation of the DRO-550.

Visit http://www.wildhorse-innovations.com for the parts and accessories to complete your DRO-550.

As always, you comments are welcome.

Gary

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.

A Bold Fresh Method of Mounting the Display LEDs

OK, so I borrowed a bit of the title from Bill O'Reilly.  I think a bit of poetic license is allowed since I have a Grand-Daughter named after him.  (No they didn't name her Bill, her name is Reilly.)

If you've received a DRO-350 or DRO-350+ kit from Wildhorse Innovations lately, you may have noticed the scraps of plastic from the display LED windows (in the case) included in the kit.  This isn't just a way for us to get rid of some plastic scraps.  These scraps can be used as spacers to raise the display LEDs so that they are closer to the faceplate.

Above is a picture of one of these scraps.  Note the lines embossed into the plastic.  They will be mentioned later.

The first step in our process is to alter slightly the order in which the DRO-350 components are installed.  As you will see later, this is an optional step, but IMHO makes the job a bit easier.  The area outlined in red in the picture below shows the area where no components should be installed until after the display LEDs have been installed.  These components include Y1, DS15, D2, D4, D5, D6, D7, R1, R2, R28, C1, C2, JP2 and U1.  If you are building a board for a DPU-550 many of these components will be omitted from your kit already.  In the case of U1 (when building a board for a DPU-550), do not install the headers that will be positioned at U1 until the final assembly.

The following components may be installed prior to installing the display LEDs, however you may find it convenient to leave them out until after the LEDs are installed. D3, JP1, C7, R27 and Q1.

The following picture shows the relationship of the spacer material to the LED when the LED is mounted on the board.  Due to variations in manufacturing, the spacer may be slightly wider than the spacing between the LED legs.  In this case, brief sanding to narrow the spacer will solve the problem.

The installation procedure is as follows:

Fill a single corner hole for each display LED mounting point with solder. The hole should be filled so that it domes slightly.  Having too little solder will make it more difficult to melt the solder in the following step.

It makes no difference with which row of LEDs you begin, but remember to begin with the LED that is closest to where the switches will be.  If you begin at the opposite end of the row of LEDs, you will have no easy way to remove the spacer after the final LED in the row is installed.  There should be three spacers included with each kit, so the spacer could remain in position under the LEDs if necessary.  I tend to be a bit of a "neat-nick" and prefer to have the spacers removed once the LEDs are installed.

Holding the spacer and the LED such that the spacer is between the board the the LED, engage as many of the remaining holes as possible.  While holding the spacer and the LED in this position, heat the solder in the corner hole.  As the solder becomes molten the LED should slip into position.  If it does not move into position easily, do not force it.  One of two things is occurring.  Either the solder is not yet molten, or the LED is not in the proper position.

BE SURE THAT THE LED IS PROPERLY ORIENTED!!!  I hate to admit that more than once I have soldered an LED into position, only to find that I have installed it upside down.

When the solder has become molten and the LED has slipped into place, carefully examine the relationship of the spacer, LED and board surface.  Be sure that the LED is level in all directions.  If adjustment is necessary, heat the solder just long enough to move the LED into position.

NOTE:  Raising the LEDs by this amount does not allow the legs of the LED to protrude completely through the PCB.  However, the end of the legs is typically at, or slightly below, the surface of the PCB.  Be sure to use sufficient solder that the solder wicks through the hole and "climbs" up the LED leg on the opposite side of the PCB.  In addition, there should be a slight "dome" on the side of the PCB from which you are soldering.

Now solder the leg if the LED that is diagonal from the leg just soldered.  Again examine the position of the LED and adjust as necessary. DO NOT solder any additional legs at this time.  By leaving the LED with only two legs soldered, further adjustments to position are easily made.

A NOTE AT THIS POINT:

As mentioned at the beginning of this article, one side of the spacer has a pattern of lines embossed into it while the other side, though somewhat textured, is basically level.  When installing the LEDs, having the side with the embossed lines up, or in other words, against the bottom of the LED makes installation easier.  If the embossed side is positioned against the surface of the PCB, the lines will have a tendency to catch on the slightly raised surfaces surrounding the holes in the PCB.  While moving the spacer with the lines against the PCB is not impossible, it is my preference that any "abuse" that might occur, occur against the bottom of the LED as opposed to the surface of the PCB.

You are now ready to install the next LED.  Slide the spacer in the direction of the next LED position so that only a quarter inch or so remains under the LED just installed.  The next picture shows the position of the spacer as the final LED in a row is being installed.  Note the generous amount of scrap with which to grab in order to remove the scrap.  Depending upon how tightly you hold the LEDs as you solder the initial two corners, the spacer may have a bit of resistance to being removed.  This is especially true if you have the embossed lines on the scrap against the PCB.

After installing all of the LEDs, make one last detailed examination of the installation.  Are the LEDs properly oriented?  Are they level with each other and reasonably well positioned in relationship to each other?  Once you are satisfied that all is correct, solder the remaining pins on all the LEDs.

You are now ready to complete the assembly of your DRO processor board.

One last task.  When the display LEDs are positioned flush against the surface of the PCB (no spacer used in the installation), the five indicator LEDs should be positioned so that they extened about 1/8" above the face of the display LEDs.  With the display LEDs raised as in this procedure, that rule of thumb no longer applies.  Again we can use our scraps of plastic.  Referencing the following picture, place the scrap on the surface of the display LEDs.  The top of the indicator LEDs should extend above the surface of the display LEDs a distance equal to about 1/2 the thickness of the plastic scrap.

Well, as Porky Pig use to say "Th, th, th, that's all foks".  I hope this article has been helpful and results in better display viability for your ShumaTech DRO.  Feel free to offer comments or suggestions, and as always, thanks for visiting us here at Wildhorse Innovations.

Gary

SO IS THE DRO-350 AND THE 16F876 PIC REALLY A DEAD-END STREET?

Several reasons for the DRO-350 being at a dead-end are given. I discuss some of them below.

A compiler for the PIC series of processors is too expensive.

While the “Official” compiler from MicroChip, the compiler with which the original code for the DRO-350 was developed (Scott had access to it at one of his employers/clients/friends), is very expensive, there are several high quality C compilers available for as little as several hundred dollars. These compilers utilize the same libraries as the MicroChip compiler (the libraries are free from MicroChip).

Several hundred dollars is not pocket change to most of us, but not particularly out of line when you are talking about keeping the DRO-350 alive in it’s present state (i.e. price).

In addition, MicroChip offers a very sophisticated Assembler as a part of it’s free Integrated Development Environment.

I have one of the third party C compilers as well as the free PIC IDE. I don’t think there is anything that can be done with the MicroChip version that can’t be done with the third party versions. Mine (the C compiler) even has support for the various In Circuit Debuggers that are available from MicroChip and other vendors.

Moving from one compiler to another is not an trivial task, but again, when we are talking about extending the life of the DRO-350 for what is probably 1000’s of existing users, a bit of effort is worth while. Portability, not just for moving from one platform (computer type, MPU type, etc) to another, but also moving from one compiler to another, is one of the reasons we use high level languages like C.

The 16F876 is “maxed” out.

Yes, the 16F876 is stretched to the limit when it comes to memory. But there is a bit of room available, and certainly enough room to correct bugs. And if the software were made Open Source (it’s supposedly been made obsolete by the DPU-550 which offers Open Source software), there would be many hands that would gladly apply their effort and imagination to getting the last few drops of functionality out of the current MPU. This has already been done by members of the group who have disassembled the DRO-350 code to make changes.

THE DPU-550, A MUST HAVE OR CAN YOU LIVE WITHOUT IT?

There has been much discussion about the “dead-end” status of the 16F876 MPU (the MPU currently found on the DRO-350). It has been stated that it is at EOL (End Of Life) for several reasons.

The DPU-550 extends the functionality, and thus the life of the DRO-350. It sports a 50mhz ARM7 processor (MPU) by Atmel and has a boxcar’s worth of memory when compared to the DRO-350’s PIC16F876A. It’s a 32 bit MPU (as compared to the PIC16F876A, which is 8 bit) which makes for much faster processing, especially when math operations are involved.

The DPU-550’s two variants give the user the option of a basic processor upgrade, with a bit of additional functionality, for a current price of around $50.00, which will include not only the DPU-550 board, but all the internal cables, etc., necessary to use the additional functionality.

The big increases in functionality come in the form of the ability to support four different scale protocols, two additional Auxiliary inputs (Edge and Tach) and the ability to communicate with a computer through a USB port.

The DPU-550 Lite can be field upgraded to a DPU-550 Full which will add two additional scale inputs, two more Aux inputs, true RS-232 and a souped up 5vdc power supply to power up to five glass scales.

Field upgrading is not for the faint of heart in that most of the components are surface mount (SMD). If you attempt it, you need very good soldering skills, the proper tools (an SMD repair station would be nice) and a bit of patience. Attempting it when the DPU-550 is “new”, that is none of the through hole components have been mounted, is “doable”. But if you’re attempting it after the DPU-550 Lite has been populated with the through hole components, you’re going to be working in some pretty tight quarters.