Sunday, July 31, 2011

Serial Cable Kits - Mk1 to Mk4 - the answer for versatile industrial connection

Now for something a little different

In my day job, connecting a PC (laptop) to various industrial devices is fairly common. As is typical of these types of devices (VVVFs, Sensors, CPUs, etc) each manufacturer will require a different cable pin-out for their devices, (and some like Siemens require different cables for different models)

When I first started in my role, the "cable kit" comprised of a couple of cardboard boxes full of cables - each cable was around 1800mm (6') long, and sometimes labelled to say what it was used for.
I consider that the "Mark 1 cable kit" - large clumsy, difficult to use, and quite heavy.

I made up the "Serial Cable Kit" - this comprised a single full length DB9 straight through cable, and a number of "dongles" which were fitted to the end to change the internal wiring configuration. Each dongle was labelled, and an instruction book allowed the user to look up the device they intended connecting to, and the manual would tell them what cable and dongle combination to use - eg Siemens Masterdrive would require cable "C1" and Dongle "D2".
Photo 1 - Mk 2 Serial Cable kit in case

This system worked for a few years - it was well received by all who used it - a number of the kits were stolen, and other parts were added as new devices were added to the plant equipment.
Since I made this kit from home, I tried to keep the costs as low as possible (using double ended connectors proved cheaper than using 2 DB9 head shells with a short intermediate cable), the carry case was one from the local K-Mart (Think Wallmart) and modified.
The new kit was a considerable improvement over the original system, but after some time, and sick of fixing/ replacing missing parts, I decided a newer iteration was in order...
Figure 2 - Mk 2 Cable kit concept drawing
If the box of cables was "Mk 1", then the original "Serial Cable kit" would have to be "Mk 2"... Mark 3 would need to be smaller again, cheaper, lighter, and more versatile...
Photo 3 - Mk2 cable and dongle on relevant instruction page
The "Mk 2" dongles were 2 DB connectors separated by a distance of around 40mm (1 3/4") with the cores between being short lengths of flexible cable.. I could accomplish the same effect using a piece of bread board (electronic prototyping board) and a number of pre-terminated jumper wires. That would significantly reduce the weight, cost, and increase the versatility infinitely. I bought some cheap breadboards off the internet and got one of my spare straight through DB9-DB9 cables. I cut the cable at the PC end, at around 400mm. In use the breadboard area would need to be close to the laptop so it was supported, not hanging off the front of a panel in a substation.
Photo 4 - Mk 2 Dongle with dongle schematic
I belled out the pins and soldered the cores to a short length of header strip in order - pin 1 at the top, pin 9 at the bottom. This was repeated for the second length of the cable (around 1500mm (5') long.
The two header strips were inserted into the breadboard with pin 1 in row 1, and the same on the other side of the center strip. - This gives each pin of the serial cable 4 holes to connect cables into - the same for each pin on the outbound cable.
Using the diagrams in the Mk 2 instructions, I know I can rearrange the jumpers to make any combination of cable schematic, and I also know 4 holes per core is enough since the most any current dongle uses is 3 cores to one pin.
Photo 5 - Mk 3 prototype configured as if Dongle 2 in place
The shields from the two parts of the split cable are joined to the backing of the breadboard underneath - Once it passes all tests, the breadboard will be enclosed in a small metal tin to complete the shielding.

The Mark 3 version sounds great  doesn't it?... meets all requirements, how could it be made any better? - it can be.

Mark 4 (or Mk IV if you prefer)
Photo 6 - Mk 4 "dongle" in place for Master drive communications
Currently the Mk 2 kit has 12 dongles in it - these are used to access over 20 different devices on site. Imagine the scenario where you are working on a fault - you need to talk to a VVVF drive, then talk to an ultrasonic sensor, then back to the drive, then to the PLC CPU... with the Mk 2 kit, you simply changed dongles as you moved from device to device... With the mark 3 you would be constantly changing the jumpers... if you're tired, distracted, you could too easily make a mistake - you could damage equipment, or at least waste time complicating your own fault-finding strategy.  I needed a way to make the Mk 3 system as easy to use as the Mk 2...
The step to Mk4 was easy - simply use the existing breadboard to hold a "dongle" which had the jumper configuration in it. Make it removable, and make it "labelled". Immediately the concept of using a DIP IC socket sprang to mind. If I used a 18 pin DIP socket, that would give me 9 pins up one side, 9 up the other, and a small space in the middle to solder in the jumper configuration. The DIP socket has a notch for Pin 1 which can be used to ensure the correct orientation when inserting it, and I could pot in the jumpers to provide a space for a label.
NB: I chose machine pin DIP socket since the pins are stronger and round - making them better for the breadboard when compared to typical cheap DIP IC sockets.

I ordered a fistful of machine pin DIP 18 pin IC sockets from Futurelec (along with some other goodies) and started planning the next design. Once the sockets arrived, the first dongles were being made.

Since I don't have a Siemens VVVF at home, I cannot show photos of the system in use, but if possible I will get one from work.

In use the new kit will comprise of the Mk3 and Mk4 parts. The Mk3 cable and base forms the base kit, and 12 jumpers will be included for new or experimental equipment. The current manual will be re-written for the Mk4 "dongles" which will need to be renamed, and stored. This new kit has more versatility than the current kit, and is significantly cheaper to make up. Each "dongle" in the Mk 2 kit costs over $7 AUD, whereas each "dongle" in the Mk 4 kit costs $0.40 AUD. The new kit is much smaller, lighter to carry, and should be cheap enough to make as a "personal issue" tool - that last bit is handy to reduce theft and loss of parts.

I keep talking about "versatility" - it's the ability of the kit to handle making a new configuration out in the field - The Mk 1 kit had none, the cables were made "as -is", the Mk 2 kit had one spare unassembled dongle of each configuration (M-M, M-F, F-F) in the kit to permit making a new dongle, whereas the Mk3 (and Mk4)have the breadboard space and jumpers to create new configuration cables on the fly.

Photo 7 - Showing size comparison for Mk 2 dongle and Mk 4 dongle
So the Mk 3 and Mk 4 work on the same principle of changing pin assignments, the difference between the Mk 3/4 and the Mk 2 is that it's done "inside" the cable, and reduces the amount of needed hardware.

Figure 8 - Mk3 and Mk4 concept schematics
There was one dongle which needed a special case... D12
All other dongles in the Mk 2 kit terminate with either a male or female DB9 connector - the Mk3 and Mk4 kit has a female connector at the end of the cable, and a miniature gender bender included for when a male connection is required... but dongle "d12" however terminates with a RJ11 connection - this is used for the HMI AnyBus equipment.
I had 2 options... option 1 was to reuse the existing "d12" dongle and simply have a "straight through" dongle for the breadboard... Option 2 is to have the 4 core cable for the RJ11 come off the "dongle" and leave the remaining 1500mm length of 9 core cable unterminated. I've made both, but look forward to testing option #2 since it makes for a more consistent approach.
Photo 9 - Mk 4 version of Dongle "d12" for 4 core RJ11
Some statistics (estimated where shown *) - excludes Siemens Simocode Pro cable and USB-RS232 Adapter from all comparisons - based on cables/ configurations to perform tasks of Mk 2 kit.

Mk 1 kit - weighed 4000g*, volume 400x400x400mm* = 64L, cost ~$400-800 - No labels, no instructions, no versatility

Mk 2 Kit - weighed 1800g, volume 360x290x70mm = 7.3L, cost ~$250 - Labelled, instructions, limited versatility

Mk 3 Kit - Weighed 300g, volume 250x200x50 = 2.5L, cost ~$45 - No Labels, instructions, versatile

Mk 4 Kit - Weighed 350g, volume 250x200x50 = 2.5L, cost ~$50 - Labels, instructions, versatile

Labour? - all costs do NOT include assembly labour - I made the Mk 2 kits myself over the period of 2 weeks working 4 hours each night (7 kits) - I've made my own Mk 3 kit, and will complete the Mk 4 kit over the next week or so... what takes the longest is writing the instructions, and hand construction of the dongles. - you should allow between 15 and 30 mins per dongle based on intermediate hand skills.
What's not shown in any of the photos is the base plate for the Mk 3/ 4 set - I'm still trying to design and construct a "flipper" to permit easy extraction of the IC sockets - I was using an IC extractor in testing, but would prefer something "captive" so it can't be lost. In the meanwhile testing continues with another piece of breadboard for the noise immunity of the Mk3 and Mk 4 designs.

If you think this is a good idea and want to manufacture them - go for it - please give credit where due though... I do when I write the manuals.