Previous blog entry: http://www.element14.com/community/roadTestApps/12385
Next blog entry 02 Wireless charging in household items - construction and wallplug efficiency
Wireless energy transfer was envisioned by Nicola Tesla and nowadays is becoming exceedingly popular for portable devices with apperance of smart controllers and LiPo batteries. A global standard has been agreed upon http://www.wirelesspowerconsortium.com/ named Qi, pronounced as [chi]. There is some analogy to wireless internet WiFi that started to boom around year 2000.
Many thanks to Farnell Element 14 and Würth Elektronik for selecting my project proposal for Texas Instruments Qi Wireless Power Evaluation Kit roadtest and making public announcements in news:
The Wireless Power Challenge for the medtech industry - Electronics Eetimes
MedTech and the Wireless Power Challenge
I implemented wireless charging of a prototype dermatology device "SkImager" (skin imager) that is useful in dermatology, oncology (skin cancer melanoma diagnostics), cosmetics, surgery, accident and burn treatment.This device was developed at the University of Latvia in Riga by the Biophotonics group lead by Prof. Janis Spigulis during EU project 2010-1013 and now is being tested by medical doctors: http://www.lu.lv/fileadmin/user_upload/lu_portal/projekti/es/2007-2013/eraf/optika/jul-nov2013.doc
It is based on Toradex NVIDIA Tegra 2 Computer Module - Colibri T20 powered by dual core 1 GHz Cortex A9 with 3 Mpixel CMOS digital camera and touchscreen interface and running WinCE.
Camera lens f=8 mm, 1/1.8" diameter, distortion 1.9%. Angle of view 58 deg. Multispectral illumination is done by LED ring at white, red 660nm, green 540nm and blue 450 nm wavelengths. Additionally, ultraviolet LEDs at 365 nm allow to induce fluorescence at longer wavelengths and infra-red LEDs at 940 nm allow to observe features not visible by eye. Crossed linear polariser technique is used to eliminate specular reflection from directly back-scattered light greatly enhancing image contrast.
Wireless charging is very attractive for medical devices because then they can be made hermetic and disinfected more easily. Contacts tend to wear with time, accumulate dust on them, oxidize. Cables break if bent too often or pulled harder and make a mess on the table.
I am observing from my mom that mobile phone charging is a real complication for elderly people. They try to plug in charger connector into all possible holes on the phone. Their hands are shaking and their eyes do not show small details clearly anymore. Extra complication is that cable fits into USB only in one position. And until next week many elderly people have already forgotten into which hole to plug in the charger cable. So wireless charging would significantly simplify mobile phone handling for older people.
Wireless charging would be great to have in something that one needs to use often for a short time and then put it back. Like handheld barcode scanners (shop, tickets, library), shaving and haircutting machines at the barber shop. Also for some electric gadget that is necessary wash often or for working outdoors.
Qi Wireless Power Evaluation kit
The evaluation kit allows to explore the Qi wireless power consortium standard. It uses the chips developed by Texas Instruments and power transfer inductors made by Wurth Elektronik. The kit was arriving by UPS from the USA and it got stuck in Latvia customs. University address was listed on the package and I could not pick it up as a private person because I am not materially responsible at the university. Value of 368$ was indicated and I would need to pay import tax from it. Also I was asked to show that I have purchased the item, which I couldn't because it was a gift. A colleague who has encountered a similar situation said that it is hopeless to get the package out from customs. And he was right. After one month UPS sent the package back to USA. Christian from Farnell kindly arranged that another kit is sent directly from the manufacturer Würth Elektronik in Germany. Latvia is in EU for the last 10 years and shipping things around in EU is free from tax.
Together with a colleague we opened the package and had fun starting to examine how the kit works. Below are our first impressions.
Transmitter board is supplied from 220V power adapter producing 5V up to 2A with micro USB connector. The transmitter board has a microcontroller on it. Board is surprisingly heavy because of thick the ferrite plate for magnetic field directing and copper wired transmitter coil.
The receiving coil is very slim and wires go directly to a power converter chip. The chip has extremely tiny (BGA) package with connections below the chip. Tiny chip is great for phones, but could be tricky to route and solder a circuit board for amateur applications. Actually the chip is produced in two different packages. The second package is little bit larger and has leadless pads (QFN 20) on the sides of the chip that can be soldered manually with some effort as it is reported by other roadtesters.
Energy is transferred wirelessly to power a load board made by Würth Elekctronik with many red LEDs connected in series driven by inductive step-up converter. This step-up circuit might be nice to study as nowadays LED stripes are becoming exceedingly popular for illumination.
Demo board LEDs go abruptly off after moving receiver coil 1...1.5 cm away from the transmitter. Looks like the threshold is not adjustable by a potentiometer and is it hard-wired in Qi standard. Also receiver coil needs to be centered pretty much (within ca 1 cm) above the transmitter coil.
Datasheets
Next step was to collect and read Element14 blog materials and TI datasheets.
It is easier to work with the evaluation kit datasheet directly than with the chip datasheets where some
values one needs to figure out from equations.
Datasheet for the Evaluation kit transmitter board can be found googling for:
"bq500212A bqTESLA Wireless Power TX EVM"
Receiver board is named
"bq51013BEVM-764"
In the datasheet jumpers are explained. Maximum current I_limit can be made adjustable.
There is a PCB layout example, but only for the tiny (BGA) YFP package.
Things I have tried
1. To measure wallplug power efficiency with a digital wallplug electricity meter.
2. To check if the receiver produces stable 5V 1A and how large is the ripple.
Is it charging through living tissue or plant leaves? The transmitter shuts down when receiver is removed and checks every 0.5s for receiver.
3. To check with an oscilloscope at what frequency coils work and with a radiofrequency spectrum analyser for producing electromagnetic interference.
4. Datasheet mentions serial communication over the wireless link. Looks like data communication is only one way from RX to TX and can not be used as a serial port link for other needs..
5. Transmitting power to a GPS precision timing and coordinate receiver placed on the roof of our institute building as a lightning protection for the rest of lab equipment.
This I successfully tried and wrote a blog entry.
6. Wirelessly charging the dermatology device "SkImager". Please read a separate blog entry.
7. Raspberry Pi based open source skin dermatology device - in progress.
Ideas for some potential applications that meanwhile came up:
1. Small general purpose Qi compatible wireless receiver adapter board with a coil that can be glued under many devices -
phones, cameras, remote controls, toys, walkie-talkies. Providing 5V output with interchangable end plugs for USB, micro
USB, round, etc. Companies Kobo and Adafruit already offers such RX board:
Universal Qi Wireless Receiver Module $14.95
http://www.adafruit.com/products/1901
2. Wirelessly charged battery pack for outdoors/camping, boat trips, construction sites.
Incorporating both TX and RX functions. RX on one side and TX on another.
Hermetically sealed without any connectors or cables.
It's internal battery can be charged by placing it over Qi compatible transmitter and battery status indicated on a LCD screen.
3. Shue/boot dryer. Inside the shue sole could be an inductive receiver and heater that would dry the shues overnight.
Electrically warmed hiking boots are already invented:
http://www.tripleblaze.com/blog/2009/11/21/heated-hiking-boot-uses-electricity-to-keep-feet-warm/
4. Items for use outdoors on the roads, roadworker jacket with built in LED warning lights, LED cap, boots with built-in LEDs.
5. Transmitting power to rotating devices like a 360 degrees rotating WiFi panorama webcam placed outdoors in a sealed box:
http://85.254.232.222/webcammob1/today.php
May be could do wireless pressure/temperature monitoring in car wheels.
6. Electric cutting/chopping board for kitchen with scale or LED lights:
http://electriggers.blogspot.com/2013/03/cutting-board-that-weighs-what-you-cut.html
7. Explosive environments. For example coal mines where danger of methane explosion is caused by electric sparks.
8. Implantable medical devices. 100...300 kHz charging frequency propagates through the tissue a few mm. It worked via 4 slices of salami and via 3 mm thick slice of apple.
9. The power could be transmitted wirelessly through a shop window glass to power some electronics box (for example mouse) fixed to the window on the street side allowing customers to interact with the infoscreen. Unfortunately, two-sheet glass window is thicker than 1.5 cm wireless power transmission distance of the Qi standard.
Wireless energy transfer by light could potentially allow to bridge larger distances. Laser diodes are energy efficient (50% electric to light power) and > 1W laser diodes are available. Laser aperture is small and beam can be well collimated for meters distance. Eye safe wavelenght is 1.5 um, but InGaAs photodetector is necessary for that wavelength. Intense light - danger of causing fire. So energy density should not be too concentrated. It could be a pad with many LEDs at 950 nm wavelength.
This wavelength is not visible by eye, but Si photodiodes have 90% efficiency peak around 900 nm. This would be something that we could study at our institute working with laser technologies and photonics.
Next blog entry:
02 Wireless charging in household items - construction and wallplug efficiency