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--- content:meshextender:prototyping_on_mk808 [21/04/2013 19:43]
Paul Gardner-Stephen [Flashing ROMs on the MK808b]
+++ content:meshextender:prototyping_on_mk808 [25/04/2013 04:57]
Paul Gardner-Stephen [2nd Generation Mesh Extender Prototype Platforms]
@@ Line 1: / Line 1: @@
-====== MK808B Android Stick PC + RFD900 Radio ======
+======= 2nd Generation Mesh Extender Prototype Platforms =======
-This is a 2nd generation prototype intended to address the physical size and slowness issues of the 1st generation.  It is also hoped that power consumption may be similar or lower than on the 1st generation through more integration in the Android stick PC.
+This page is for concepts for 2nd generation prototype intended to address the physical size, physical robustness, slowness issues of the 1st generation.  It is also hoped that power consumption may be similar or lower than on the 1st generation through more integration in the Android stick PC platforms being considered, but it accepted that power consumption will initially be higher.
-It would be really nice if we discovered some spare GPIOs on the 808B that could be used to control the RFD900.
+Objectives:
+  * 24-hour run-time.
+  * Fast CPU for good Rhizome signature verification performance, and generally low-latency operation.
+  * RFD900 radio connected by USB for UHF packet radio.
+  * Powered by nominal 12v input for car charging.
+  * Full powered USB port for charging phones.
+We are considering a few options for this, which are described below.
+Most of these are centred around the low-cost low-power Android stick-PCs manufactured by Tronsmart (http://www.tronsmart.com).
+===== Comparing Power Consumption of the various devices =====
+==== Summary ====
+An MK808B will use about the same amount of power as the TP-LINK WR703N platform we are currently using, but with much, much better performance.  This assumes that servald will consume less than 0.3W when running on an MK808B.
+Total power budget will be between 1.0W and 1.3W, plus the power to run servald.
+An aggregate average consumption of 1.3W is probably reasonable.
+Assuming an 80% efficient power supply, and 24 hours of endurance, this indicates that we will need a 40Wh battery.
+To allow for charging a typical phone, we should allow another 10Wh, for a total of 50Wh for a system that can endure and support a smart-phone for 24 hours.
+We need to test the assumption about servald energy consumtion to have confidence in these figures.
+What is pleasing is that the MK808B does NOT use the 1.1W - 2.2W when idle that some sources on the internet have claimed.
+=== Processing platform ===
+The TP-LINK WR703N + Wi-Fi AP+ad-hoc + USB hub + USB memory stick uses about 1W to run servald, minus USB serial adapter and RFD900 radio.
+The MK808B, not running servald, and Wi-Fi in AP mode only (we don't know how to do simultaneous ad-hoc + AP uses on it) uses about 0.75W, less than the WR703N.  But servald running will presumably push that up somewhat.
+The MK802ii uses about 1W to do the same job as the MK808B, which is more than the MK808B uses.  So the MK802ii is out on the basis of inferior power consumption and performance compared with the MK808B.
+The MK808B, apart from the lack of simultaneous AP+ad-hoc Wi-Fi looks like the clear winner at this stage, provided that servald doesn't consume lots of power.
+=== USB/Serial adapters ===
+The CP210x adapter uses about 0.14W, while the FTDI adapter cable uses about 0.12W. However, the cable is too large for the slight power saving that is offers.
+=== RFD900 Radio idle consumption ===
+The RFD900 adds between about 0.04W and 0.3W when operating at a TX power of 100mW.  Average consumption could not be easily measured with the bench supply that these tests were performed with.
+==== Raw Measurements ====
+  * MK808B (idle, Wi-Fi client mode, HDMI display connected and on, Serval Mesh not installed, no serial adapter plugged in): averaging 0.187A - 0.198A @ 4.995V = 0.94W - 0.99W
+  * MK808B (idle, Wi-Fi client mode, HDMI display disconnected, Serval Mesh not installed, no serial adapter plugged in): averaging 0.145A - 0.155A @ 4.995V = 0.73W - 0.77W
+  * MK808B (idle, Wi-Fi client mode, HDMI display disconnected, Serval Mesh not installed, CP210x serial adapter plugged in, no RFD900 attached): averaging 0.173A - 0.180A @ 4.995V = 0.87W - 0.90W
+  * MK808B (idle, Wi-Fi AP mode, HDMI display connected and on, Serval Mesh not installed, no serial adapter plugged in): averaging 0.187A - 0.201A @ 4.995V = 0.94W - 1.01W
+  * MK808B (idle, Wi-Fi AP mode, HDMI display disconnected, Serval Mesh not installed, no serial adapter plugged in): averaging 0.146A - 0.157A @ 4.995V = 0.73W - 0.79W
+  * MK808B (idle, Wi-Fi off, HDMI display connected and on, Serval Mesh not installed, no serial adapter plugged in): averaging 0.143A - 0.144A @ 4.995V = 0.71W - 0.72W
+  * MK808B (idle, Wi-Fi off, HDMI display disconnected, Serval Mesh not installed, no serial adapter plugged in): averaging 0.102A - 0.103A @ 4.995V = 0.51W - 0.52W
+  * MK808B (idle, Wi-Fi client mode, HDMI display disconnected, Serval Mesh not installed, CP210x serial adapter plugged in, RFD900 attached (TX @ 100mW), but no link): averaging 0.209A - 0.26A(but jumping between 0.21A - 0.26A wildly, presumably based on whether it is TXing) @ 4.995V = 1.04W - 1.3W
+  * MK808B (idle, Wi-Fi client mode, HDMI display disconnected, Serval Mesh not installed, CP210x serial adapter plugged in, RFD900 attached (TX @ 100mW), link but no traffic): averaging 0.22A - 0.27A(but jumping between 0.22A - 0.27A wildly, presumably based on whether it is TXing) @ 4.995V = 1.05W - 1.35W
+  * MK808B (idle, Wi-Fi client mode, HDMI display disconnected, Serval Mesh not installed, FTDI serial adapter plugged in, no RFD900 attached): averaging 0.168A - 0.175A @ 4.995V = 0.84W - 0.88W
+  * MK808B (idle, Wi-Fi client mode, HDMI display disconnected, Serval Mesh not installed, FTDI serial adapter plugged in, RFD900 attached (TX @ 100mW), link but no traffic): averaging 0.210A - 0.25A (but jumping around wildly in that range) @ 4.995V = 1.05W - 1.25W
+  * FTDI cable + RFD900 (TX @ 100mW) with link but no traffic: 0.048A - 0.09A @ 4.995V = 0.24W - 0.45W
+  * FTDI cable + RFD900 (TX @ 250mW) with link but no traffic: 0.037A - 0.12A @ 4.995V = 0.19W - 0.60W (but peaks are likely reduced due to sampling issues in our test environment).
+  * CP210x cable + RFD900 (TX @ 100mW) with link but no traffic: 0.066A - 0.1A @ 4.995V = 0.33W - 0.50W
+  * MK802ii (idle, HDMI display connected, Serval Mesh not installed): 0.21A - 0.30A @ 4.995V = 1.05W - 1.50W
+  * MK802ii (idle, HDMI display disconnected, Serval Mesh not installed): 0.20A - 0.30A @ 4.995V = 1W - 1.50W
+  * TP-LINK WR703N (idle, no USB hub, memory stick, USB serial adaptor or RFD900 radio): 0.099A - 0.110A @ 4.995V = 0.50W - 0.55W
+  * TP-LINK WR703N (idle, Wi-Fi in simulatenous ad-hoc & AP mode, USB hub, memory stick, running servald, no USB serial adaptor or RFD900 radio): 0.191A - 0.21A @ 4.995V = 0.96W - 1.05W
+====== MK808B Android Stick PC + RFD900 Radio ======
 Pros:
@@ Line 17: / Line 81: @@
     - no connection by ad-hoc mode phones
   - It runs Android instead of a bare Linux OS, making life a bit more complicated and development slower.
-  - It might end up using a lot of power, since the 808B isn't intended to be battery powered.
+  - It might end up using a lot of power, since the 808B isn't intended to be battery powered (reports on the net suggest 2.2W typical, and around 1.1W if the CPU is derated down to 265MHz, but we need to find out how to control this).  This means we have a total power budget several times higher than with the original WR703N solution (0.3W without Wi-Fi apparently, and probably well under 1W even with Wi-Fi on).  Total power budget including radio we estimate to be <3W, so 24 hour run-time requires 72Wh battery, whereas 30Wh would probably have been enough with WR703N.
 ===== Flashing ROMs on the MK808b =====
@@ Line 38: / Line 102: @@
 http://www.armtvtech.com/armtvtechforum/viewtopic.php?f=111&t=1402
-===== Potential ROMs for Mesh Extender Prototypes =====
+===== Potential ROMs for MK808B-based Mesh Extender Prototypes =====
 We need CP210x serial support, and Wi-Fi hotspot, and ideally simultaneous Wi-Fi access point operation.  "Monitor and operate" could probably do in place of simultaneous ad-hoc.  Hotspot only would do in a pinch.
@@ Line 58: / Line 122: @@
 http://www.armtvtech.com/armtvtechforum/viewtopic.php?f=111&t=1402
-But Wi-Fi/Bluetooth support uncertain.  Wi-Fi seems to work in the lab in client mode. Hotspot mode to be tests.
+We have confirmed that cp210x support works, and can talk to an RFD900 radio with this ROM.
+But Wi-Fi/Bluetooth support should work, but remains to be tested.  Wi-Fi seems to work in the lab in client mode. Hotspot mode to be tested. Also, need to test the performance of the Wi-Fi given the allegations of poor performance that have been made in various fora.
 ===== MK802ii =====
-This is the older generation of the same device.  It runs @ 1GHz with an older core, lacks Bluetooth and depending on the version has either 512MB or 1GB RAM.  Certainly enough for what we need.
+This is the older generation of the MK808B.  It runs @ 1GHz with an older core, lacks Bluetooth and depending on the version has either 512MB or 1GB RAM.  Certainly enough for what we need. It might (or might not) have lower power consumption.
 Putting a Debian image on is easy: http://romanrm.ru/en/a10/debian
@@ Line 108: / Line 174: @@
 With this we were able to talk to the RFD900 easily from our MK802ii.
-==== Radio Modules & Antennae ====
+====== Radio Modules & Antennae ======
-RFD900 radios are AUD$62 wholesale (orders above 20 or so units).
+RFD900 radios are AUD$62 wholesale (orders above 20 or so units, but check with RFDesign before ordering).
+From an antenna perspective, we are keen to have two antennae for diversity, and to orient these antennae at 90 degrees to each other, so that orientation of the Mesh Extenders is less critical, e.g., when being carried by hand, in a back-pack or in a vehicle.  The idea is to make it as easy to use as possible.
+===== Flexible strip dipole antennae =====
 Of the antenna options that rfdesign stock, the dipoles have much better performance due to ground-independence (less local noise induced on the receiver) and reduced transmission losses through reflection.  The flexible PCB dipoles (http://store.rfdesign.com.au/rfdflex1-900mhz-flexible-pcb-antenna-no-cable/) are probably the best.  These are $7.95 each, plus coax cable and connectors, cost to be determined.
@@ Line 117: / Line 187: @@
 That makes total radio cost $62 + $7.95 + $7.95 + $6.45 = about AUD$85 in quantity.
+One challenge with this arrangement is that the battery (remember that LiFePO4 batteries contain iron) should be ideally around 5cm from the dipoles to minimise detuning.  This would suggest a larger enclosure size than we were hoping for.
+===== Corner-mounted monopole antennae =====
+This was a concept that Seppo at RFDesign suggested, having two monopole antenna on corner-mounted ground planes.  These would be on truncated corners of the relaxed cube shape of the enclosure.
+====== Enclosures/Cases ======
+===== MyTouch 3G retail box =====
+We were looking at using the boxes that T-Mobile branded HTC MyTouch 3G Sense come in, because we have a few, and they are a nice hinged plastic case big enough to fit an MK808B, 30Wh battery and RFD900 radio.  But it turns out that with our larger battery requirements, and the clearances required for the antennae that they are probably too small.  That form factor is still possible in a future version where we can commit more resources to optimising behaviour, in particular of antennae.
+===== Plastic cases from a Chinese manufacturer =====
+There are a few options we are looking at by hunting around on AliExpress.
+The most promising at this time has external dimensions of 220x210mm by 130mm high, and a carry handle on the top.  Internal dimensions are 208x200x126mm.
+It does weigh 490g, which is more than I would like, as it would make for a total weight of >1.5KG by the time we have a ~1KG 70-80Wh battery in there.  One presumes that it must be quite robust to weigh that much for such a small box.
+But it will probably be fine for now, either that or we continue to buy plastic lunch boxes from supermarkets or discount variety stores.

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