Paul Boddie wrote: > but you could probably feel "validated" by > choosing it if all these other products influence you in some way.
Yes, the Nordic chips are rather popular. This also means that nicely matched baluns are readily available :) Alas, not two with the same package, so the RF balun will become a part without second source. I've now updated the schematics: http://downloads.qi-hardware.com/people/werner/anelok/tmp/anelok-20160207.pdf There may still be loose ends (e.g., if nRF51 and cMCU end up on the same side of the PCB, I may want t swap RF_CRRT and RF_CTRR), but this would by and large be the design. There are a number of options in the RF part (sheet 10): - on the left side, we have components for a DC-DC converter to provide the internal 1.8 V supply from the system's 3.3 V. This should reduce power consumption by maybe up to 30% while the radio interface is active (i.e., listening or sending). Not sure if this is actually worth the effort, but it can't hurt to have the option for now. If the DC-DC converter turns out to be overkill, we can use the same layout for the LDO setup, by removing C24, L2, and L3, and (optionally) reducing C25 to 100 nF. - for "wall-clock" (RTC) timekeeping, there are a few options, too: 1) use a low-power 32768 Hz crystal (0.4 uA), 2) use the voracious 16 MHz crystal (15 uA, which is high, but still surprisingly low given that the 16 MHz oscillator draws hundreds of uA in other modes), 3) use an external oscillator, or 4) maybe use an external trigger ? For 4), we already have an RTC in the sMCU, so that one could provide an occasional trigger, provided that a) some jitter is allowed (this would have to go from sMCU to cMCU and then to RF), b) it's okay to sometimes lose a trigger (e.g., if some other communication is in progress at the time), This option needs further study. For 3), we could use a clock output from the sMCU. Drawbacks of this approach would include having a permanently active "long" trace on the PCB, the need to coordinate rfkill with the sMCU (to avoid driving the hypothetical clock signal while VRF is shorted to ground), and the need to free up one GPIO. Avoiding the crystal would mean a potential BOM cost saving of about 40 US-cents at 1000 units, 30 at 10k. For further study. - I also increased the capacitance of some decoupling capacitors (C30, C32), to match similar parts used elsewhere. This is to keep the number of different parts down. - the nRF51822 itself comes with various memory configurations, with 128 or 256 kB Flash and 16 or 32 kB RAM. I've specified the biggest (and most expensive), to be sure to have enough room. This can be optimized later. Speaking of cost, the component cost (without PCB, case, battery contacts, etc.) is currently at USD 25.40 @ 100 units, USD 22.51 @ 500 units. Some published quantity discounts don't go beyond 100 units, so prices for 500 units and beyond may go down a little. This is a bit on the high side of the acceptable range. The relatively high cost is caused less by fancy chips but by the price of the OLED jumping up from USD 4.85 @ 100 (2014-2015) to USD 8.26 @ 100 in 2016. http://downloads.qi-hardware.com/people/werner/anelok/tmp/anelok-pie-usd-500-20160207.pdf Maybe it's time to look for second sources, e.g., - Shineworld Innovations GLO13-D-M2001 http://www.alibaba.com/product-detail/1-3-Graphic-Blue-Color-128x64_60018968100.html?spm=a2700.7724857.29.1.kwI3WO&s=p It says "blue" but looks white-ish. In any case, it seem to exist in white: http://p.globalsources.com/IMAGES/PDT/SPEC/239/K1077987239.pdf Note: different controller, apparently not entirely compatible: https://forum.arduino.cc/index.php?topic=259186.0 - Formike KWH0130UL01 http://www.formike.com.cn/product/60244849708-219498402/Formike_1_3_inch_flexible_OLED128x64_KWH0130UL01.html In any case, this type of OLED is very common, so if there's a problem with Eastrising, it shouldn't be hard to find a drop-in replacement. - Werner _______________________________________________ Qi Hardware Discussion List Mail to list (members only): [email protected] Subscribe or Unsubscribe: http://lists.en.qi-hardware.com/mailman/listinfo/discussion
