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There were many academic things to do as the study year came to end in Latvia. Finally, there is some time for pushing forward Wireless Power Challenge project.
On June 10 had time to make a list and order parts from Farnell using their kindly offered 200 EUR voucher. Webshop was running perfectly. Shopping cart did not timeout as it oftern happens in some other online shops.
RX coils
I have ordered spare the RX coil from Wishay that was recommended in the TI RX chip datasheet and in the RX module could not read the coil part number as it was taped to plastic with part number facing down. Wurth Electronik pointed out that their coils are used in the EVK and were so kind and sent 3 types of their RX coils for free with an express delivery.
Receiver coils have a FERRITE plate that concentrates and shields magnetic field energy. Probably ferrite is chosen instead of metal because of smaller hysteresis loss and insensitivity to DC magnetic fields. The shield is brittle. We wanted to see if the coil could be bent slightly. That resulted in a broken corner. See the photo below.
I did not see weight specified in manufacturer datasheets. Weight is one of important parameters for portable electronics. For example a miniature toy helicopter weighing 20g would not be able to carry it during flight. I was curious to measure it. Wishay coil is the most heavy one weighing 7 grams. Smallest WE coil weight was 4 grams.
In Wishay coil central wire comes back and crosses the coil.This increases thickness to 1.5 mm. In mobile applications is often an issue.
WE has engineered the central wire into a slit in a ferrrite shield making it a more thin construction. WE ferrite shield is slightly flexible. It could be probably softened by heating and bent into slightly round shape to fit cylindrical enclosure.
Wishay coil has 9.7 uH inductance, both larger WE coils have 12 uH and the smallest WE coil has 16.7 uH. Surprisingly, when I soldered them to the RX board, all of them worked and transfered power without necessity to change the capacitors on the RX board. This is good news for roadtesters. That we don't need to spend time for resoldering SMD capacitors.
Physics say that with different inductancies the resonance frequency should change. I think it works because RX and TX coils are strongly magnetically coupled so there is no individual resonance frequencies of each resonance contour, but, insterd, it is one resonance frequency for the two-coil system. I connected oscilloscope and could clearly see that frequency is not fixed. It changes in small steps with load and coil separation. This is called in datasheet "Dynamic Effciency Scaling" and "Dynamic Rectifier Control"
Extremely clever system!!! Looks like the tiny chip is as smart as a microcontroller.This means that energy transfer is always optimal and devices that are being charged can have quite large manufacturing scatter.
RX and TX chips
Receiver chips I ordered same as in the RX board but in RHL package BQ51013BRHLR.
If I new at that time then would have ordered also LiPo charger chip BQ51050BRHLR. I ordered it as a free sample now.
To my surprise typing wireless transmitter chip
BQ500212ARGZT
in http://lv.farnell.com/ produces no result.Just BQ500212AEVM-550 EVALUATION MODULE appears.
Same happens in UK and German Farnell pages. Is listed in Farnell USA page.
So, it looks like a transmitter with the BQ500212A chip is not possible order from Farnell in Latvia. May be need to search for another chip.
So I deleted the transmitter coil and FETs from the order list. And will use the transmitter board from the kit or later buy Qi charger from Samsung.
Later I ordered wireless transmitter chips from TI as free samples as roadtester Eduardo has designed PCB and may be I will mahe a PCB too.
I also ordered LEDs (UV, RGB, white, IR) for multispectral skin illumination and multichannel LED driver chips.
Logitech C270 Webcam was way to overpriced in Farnell (40 EUR) compared to computer shop prices (22 EUR). I will get a webcam and Arduino Nano myself.
Also ordered Raspberry Pi model B that could do webcam image processing with OpenCV and control multispectral LEDs.
As one of the next things I will try if wireless power evaluation kit can drive Raspberry Pi with a webcam and WiFi donge.
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Below is the list of parts from Farnell Element 14
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Wireless power receiving components:
2056596 3 VISHAY DALE IWAS4832FFEB9R7J50 INDUCTOR, 9.7UH, 5%, RADIAL
2400022 760308103202 WURTH ELEKTRONIK CHARGING COIL, 12UH $10.88
2400023 760308103203 WURTH ELEKTRONIK CHARGING COIL, 12UH $10.26
2400024 760308103204 WURTH ELEKTRONIK CHARGING COIL, 16.7UH $10.26
2146062 3 TEXAS INSTRUMENTS BQ51013ARHLT IC, WIRELESS PWR RX MGR, 20QFN, Chip producing regulated 5V
If I new at that time I should have ordered Wireless RX chip allowing to directly charge LiPo without conversion to +5V. That would allow to increase overall efficiency. It is pin compatible to 5V RX chip.
TEXAS INSTRUMENTS BQ51010BYFPT INTEGRATED WIRELESS RECEIVER
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LiPo charger and 5V boost regulator
2323721 2 TEXAS INSTRUMENTS BQ24075TRGTT BATTERY CHARGER, LI-ION, 1.5A, QFN-16
2102677 1 TEXAS INSTRUMENTS LMZ10503TZE-ADJ/NOPB BUCK, 5.5VIN, 3A, 1MHZ, ADJ, 7TOPMOD
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Multispectral LEDs
1655537 4 OSA OPTO LIGHT OCU 400 403 OS LED, SMD, CERAMIC, UV 403NM
9707816 20 SHARP GL100MD1MP1 IR EMITTER, SMD, 940NM
2290441 20 KINGBRIGHT L-53F3C LED, IR, 5MM, 940NM
2290345 10 KINGBRIGHT KPTD-3216SURCK-01 LED, 1206, DOME, REV.TAPED, RED
2112155 10 MULTICOMP 703-1039 LED, RGB, 5050
1648562 10 VISHAY VLMW41S1T1-5K8L-18 LED, SMD, PLCC2, WHITE
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Constant current LED driver chips
1755247 2 TEXAS INSTRUMENTS TLC5916ID IC, LED DRIVER LINEAR 16-SOIC
1755248 5 TEXAS INSTRUMENTS TLC5916IPW. IC, LED DRIVER LINEAR 16-TSSOP
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ARM board
2191863 1 RASPBERRY-PI RASPBRRY-MODB-512M SBC, RASPBERRY PI, MODEL B, 512MB
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Parts arrived on the next day! Extremely fast delivery! Thanks!
Next blog entry: 07 Wireless charging of dermatology device "Skimager"