Here’s one of the old modems from my spares bin, a Vodafone Mobile WiFi R207. This is just a rebranded Huawei E5330. This unit includes a 3G modem, and a WiFi chipset, running firmware that makes this a mini-router, with NAT.
The back has the batter compartment & the SIM slot, with a large label showing all the important details.
A couple of small Torx screws later & the shell splits in half. All the electronics are covered by shields here, but luckily they are the clip-on type, and aren’t soldered direct to the PCB.
Once the shield has been removed, the main chipset is visible underneath. There’s a large Spansion MS01G200BHI00 1GBit flash, which is holding the firmware. Next to that is the Hi6758M baseband processor. This has all the hardware required to implement a 3G modem. Just to the right is a Hi6521 power management IC, which is dealing with all the power supplies needed by the CPU.
The RF section is above the baseband processor, some of which is hiding under the bits of the shield that aren’t removable.
There’s a socket onboard for a standard Mini-SIM, just to the left of that is a Hi6561 4-phase buck converter. I would imagine this is providing the power supplies for the RF section & amplifier.
Not sure what this section is for, all the parts are unpopulated. Maybe a bluetooth option?
The other side of the PCB is pretty sparse, holding just the indicator LEDS, button & the WiFi Chipset.
The chipset here is a Realtek part, but it’s number is hidden by some of the shield. The antenna connection is routed to the edge of the board, where a spring terminal on the plastic case mounted antenna makes contact.
As the first USB hub I was using was certainly not stable – it would not enumerate between boots & to get it working again would require waiting around 12 hours before applying power, it has been replaced. This is a cheapie eBay USB hub, of the type shown below.
These hubs are fantastic for hobbyists, as the connections for power & data are broken out on the internal PCB into a very convenient row of pads, perfect for integration into many projects.
I now have two internal spare USB ports, for the inbuilt keyboard/mouse receiver & the GPS receiver I plan to integrate into the build.
These hubs are also made in 7-port versions, however I am not sure if these have the same kind of breakout board internally. As they have the same cable layout, I would assume so.
Here is a closeup of the back of the connectors, showing a couple of additions.
I have added a pair of 470µF capacitors across the power rails, to further smooth out the ripple in the switching power supply, as I was having noise issues on the display.
Also, there is a new reset button added between the main interface connectors, which will be wired into the pair of pads that the Raspberry Pi has to reset the CPU.
This can be used as a power switch in the event the Pi is powered down when not in use & also to reset the unit if it becomes unresponsive.
The final part for the battery pack has finally arrived, the PCM boards. These modules protect the cells by cutting off the power at overcharge, undercharge & overcurrent. Each cell is connected individually on the right, 12v power appears on the left connections. These modules also ensure that all the cells in the pack are balanced.