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Host Module Status: 160501

Posted: Sun May 01, 2016 1:02 pm
by softbaugh
Right now the host module PCB is in its third prototype (v0.3). Here is a the history of the various prototypes so far:

v0.1: Our first effort worked well as a phone host board, but had some unexpected response of the charger to the input protection circuitry. This design had an input PTC, but at low input voltages, current spikes from the charger kept bouncing off the limits of the PTC, causing it to whine at an audible frequency under low input voltages (around 6 V to 8 V depending on the state of charge). Since one of the design goals is to charge the battery under a very wide range of input voltages without excessive conversion losses, we decided to drop the PTC and just use an input Schottky diode to provide reverse protection.

Shane, the concept advocate, has the first v0.1 board ever made, for him to keep as a museum piece. The Kickstarter video shows the second v0.1 board in action.

v0.2: This prototype formalized the fix to the low input voltage whine, and replaced a lot of the components with lower cost options. This board design is two-sided, meaning that components are on both sides of the board. This makes for a small footprint, but it is more expensive to produce than a single-sided design. With a proprietary design, the margins usually cover the difference and smaller produces a more favorable end-user impression, but for an open-source project ease of assembly and reduced production cost carries more weight. We stuffed one unit of this design a couple of weeks ago and sent it to Shane last week for testing.

We will release the design files for this version also, but probably won't go into production with it unless there is enough demand to justify a special production run.

v0.3: This prototype is a single-sided version of v0.2, but other than being about 50% larger in the shorter dimension, is functionally identical to v0.2, and uses the same schematics and bill of materials. The PCBs for this version are being fabbed now, we'll probably stuff two of them this week. We expect to go into production with this version.