e-Gizmo New Low Cost Bluetooth Module

Before we introduced our first Bluetooth module, our EGBC-04, I actually made several attempts to hack some mainstream USB Bluetooth dongle to see to possibility of converting them for UART functions. The driving motivation is low cost. USB Bluetooth dongles are produced in huge quantity. Economy of scale coupled with fierce competition from rival manufacturers essentially drove the prices of these devices so low; it could just not get any lower

The effort was hampered by the inavailability of information regarding the chipset. Obviously, these info were available to OEM customers and manufacturers only and not to some lowly and pesky experimenters like me. If I can’t get the datasheet, I reasoned, there is no chance I could get the development tools either. And so I abandoned the idea and settled for the imported EGBC-04 bluetooth module.

EGBC-04 is a very good performer. It is just the price that bothers me. Being hobbyists myself, I just know too well that that its price tag is a bit too much to the pocket of an average pinoy hobbyist.

e-Gizmo new BlueTooth module is a Class 2 bluetooth device with SPP profile. It is used mainly as a wireless cable replacement between microcontroller and other devices using serial UART for the data exchange.  It is  based on National Semiconductor’s feature packed BlueTooth chip, the LMX9830. This chip made it possible for e-Gizmo to produce this BlueTooth module that carries a price almost half cheaper that the current EGBC-04 BlueTooth Module.

LMX9830 Bluetooth Chip

I’ve been looking at National Semiconductor’s LMX series Bluetooth solutions as a possible low cost alternative. But there is a problem. Most distributors will not entertain small orders (of less than MOQ Minimum Order Quantity). For a few that are willing, a hefty premium is added on top of the price, which will make these devices unattractive once again.

Fortunately, we met a supplier who agreed to sell us the LMX9830 in small quantities, and in what appeared to be a reasonable premium. The stage is set for our low cost Bluetooth module.

The LMX9830 BlueTooth chip is housed in a tiny 60 pin BGA package. Not an appealing thing to DIYers at large. There is in fact a fully verified version in module form, the LMX9838, but the small size of this module is still considered by many as not experimenter friendly, and cost about twice as much.

Designing the LMX9830 based BlueTooth Module

As soon as the design process is started, we are immediately faced with a hurdle- the LM9830 chip is available only in 60 pin BGA package with dense 0.8mm pin spacing. This presented a tough challenge when the PCB was laid put. Pins underneath the LMX9830 chip component are routed without using vias . With space between pins too restricted, every pin connections must find its way out using route paths that allows just one trace to wade through it.

Furthermore, to keep the cost low, I made everything using two layer pcb only with footprint about the size of a 28 pin DIP package. I used size 0603 for the passive components, but even these tiny chip components seemed to be too large for the layout. After several days of intense layout work, I finished the PCB layout with a pattern I thought should keep the LMX9830 happy enough to do a good job.

PCB layout is a complex job, especially when you are working with high frequency circuits where the PCB layout itself plays a significant part in the performance of the circuit. Notwithstanding my several years of experience, I seldom make PCB that worked great outright straight from paper design. Some modifications are always needed. For this reason, I always verify new PCB layout using handmade PCBs to check and correct layout problems before sending it for outside fabrication. Not with this one though. The layout is too dense, there is little chance I could ever successfully hand make a usable PCB. This one went straight to the professional PCB fabricators for volume production.

True enough, almost as soon as the first PCBs arrived, I quickly spotted some layout problems. A connection is missing, and some layout sensitive components appeared to be inadequately positioned. Things are not just as obvious when they are still on papers (sigh..). For a while I thought these PCBs are going straight to the trash. Luckily, the LMX9830 did not seem to mind the errors. With a short jumper wire taking care of the missing connection, the Bluetooth module performed quite respectably after some spirited tweaking (that includes antenna tuning).

e-Gizmo BlueTooth module occupies a footprint just slightly larger than a standard 28 pin DIP package.

The module terminals are arranged and separated matching the mounting holes of a 600mil wide  IC DIP package. A short prototyping wire completes a connection missed out during the layout works of the PCB.

Assembly Woes

This bare PCB board shows clearly the crowding of closely spaced pcb traces, each one only about 0.1mm wide. Most of these traces have to wade through the pins of LMX9838 IC that are separated by a mere 0.8mm.

The BGA package posed a serious problem. How do I hand solder this chip? We do not have the equipment and experience to do this kind of assembly job. I did what a typical clueless designer does when faced with a question like this: Google. Yet Google failed to yield any useful link (maybe I did not search just hard enough). Found none that I liked, actually. There are in fact many suggestions circling around, like the ones that uses a toaster oven, but I find them just too risky.

I also tried asking several friends who might have worked with BGA. Those who are in the know said a reflow oven is necessary. How about hand soldering? They think I am nuts just to even think about this.

While everyone else says it cannot be done, I actually believed the opposite. Try, experiment, if it did not work, try some more. That’s what nuts like me do. Nuts don’t give up easily. To cut the story short, I actually did it, costing me five LMX9830 chips to earn the new skill.

Production of e-Gizmo LMX Bluetooth module is scheduled to start within the first week of January 2010, with first few units available for sale by the middle of January.

The LMX9830 securely mounted on the PCB after a successful hand soldering job. I destroyed five chips before I finally figured out the right way to hand solder these chips.