So what progress have we made ?
While PeterJ has been able to find a very promising manufacturer specialized in small series production I have been busy with adding a few smaller improvements to the shield design.
- I reduced the board size by almost 20 %. The main reason for this was that PCB pricing is usually calculated in $/area and this board having 2oz copper is more expensive already compared to the regular 1oz that are available from the usual (here in the US) hobby/low volume PCB houses such as OSH Park and BatchPCB. One can easily see the impact of the board size and compare prices using the usual online calculation tools. I based my pricing on the CustomPCB.com site online tools. They offer 2oz copper thickness, however this is only interesting for a larger number of boards. If you only need a hand full you’ll have to look somewhere else. We are loking at an initial batch of 50 so that was not a problem.
- The Murata Inductors are not available anymore and had to be replaced. The Panasonic inductors that were suggested by the manufacturer that PeterJ contacted are in fact better than the Murata. Not only are they shielded but have a roughly 30% reduced RDC which means in essence that they transform a lot less energy into heat. The shielding helps reducing EMI and the shorter signal paths of the smaller board help reducing EMI as well.
- The barrel jack has been replaced with a screw terminal for greater flexibility.
- I added 2 solder jumpers on the top side of the board to be able to disable the pull-up resistors. In my own project I am using 5 shields on about 4m of CAT5 Ethernet cable. The 1.8k pull-up resistors, while still in spec, are already on the lower side and when using several shields one can quickly run into I2C problems. I had to remove the pull-up resistors on 4 of my 5 shields and jumpers would have definitely made that easier. Particularly if one later on decides to use the shield standalone. Hand soldering another set of 0402 package resistors back onto the board is not my cup of tea and in this case solder jumpers just make for a better design.
- I added another set of two solder jumpers to the bottom side of the board to provide compatibility with some of the more recent additions to the family of Arduino Boards. The old shield was compatible to the Duemilanove and UNO R2. The new shield, will also accommodate the UNO R3, which has the newer headers that offer more contacts. The jumpers also allow to “switch” over to the newer SDA/SCL contacts that the Arduino team now has conveniently placed exactly on the opposite side of the newer boards, e.g. the Leonardo and Due.
- With the exception of the thermal vias under the LT3496 all other vias will be tented.
The only thing that will not really be Arduino compatible is the mounting holes. These do not follow the usual Arduino pattern anymore, but I doubt that is a problem. If a user wants to stack the shield onto an Arduino, the holes are not of much use anyway and if the shield will be used standalone, compatibility with the Arduino hole locations is a rather useless feature.
Whether the first batch of 50 boards that we have in mind will be of the newer design has yet to be decided. It may not happen. I am rather reluctant to submit an untested design to manufacturing even when the changes are not really that significant. More than 20 years of engineering experience have taught me that lesson 😉 I’ll need to see how quickly I can assemble a prototype and test it. Below is a screenshot of the improved version.