Radio Days – 40 Years of Experimental Wireless From Crystal Sets to CC1110s – and everything in between.Ken Boak OSHUG C4CC 26th January 2012
Some Milestones• 1965 August - born• 1970 First crystal set – with dad’s help• 1972 Building a Transistor Radio – a 1972 Ladybird book.• 1974 Ferranti ZN414 TRF receiver – school electronics club.• 1978 Redifon RF Communications receiver “Radio Moscow”• 1980 MacGregor radio control, DIY walkie talkies• 1981 Illegal 27MHz CB “Citizens Banned”• 1982 Visited Vintage Wireless Museum in Dulwich• 1982 DIY FM bugs• 1984 Wireless transmission of ZX81 “Save”• 1986 – 1994 – Time out - worked for BBC Research Department on HDTV!• 1998 Low power wireless gas meter datalogger• 2002 Low power & GSM telemetry/telematics• 2005 Wireless signalling device for US Realtors (Estate Agents)• 2006 Hacked Wireless thermostat• 2008 Hacked Lidl Remote Power Switch – Snap Rat• 2009 50uA Super regenerative receiver• 2010 Wireless Energy Monitor with CC1110• 2011 Low power wireless Nanode with RFM12B
Early Beginnings – Crystal Sets • Wireless was often your first introduction to electronics and making things • Bernard Babani Publishing • Inexpensive softback books • Components readily available and cheap • Ideal for experimentation – I made a crystal set transmitter by mistake! • An early example of Open Source Hardware!
Building a Transistor Radio - 1972• A design I made from a 1972 Ladybird book “Building a Transistor Radio”• Indebted to Henry for his reconstruction and photos.• http://homepage.ntlworld.c om/henry01/ladybird_radio/ ladybird_radio.htm
Super-regenerative Receivers• Been around since 1920’s – adapt well to modern semiconductors and integration• Very low parts count – thus cheap to make <$1• Ideal at low data rates for consumer gadgets• Very low power operation (1uA – 50uA possible)• Possible to get transmitter function for “free”• Tricky to design, theory is a bit heavy going• Can and probably will cause in-band interference
Super Regenerative circuit – 1920s• Based on regenerativecircuit patented by EdwinArmstrong in 1914•Disputed for 12 years byLee De Forest•One active element –atriode valve acting as RFoscillator/amplifier•Very low parts count•Easy for hobbyist to make•Better sensitivity andselectivity than crystal set•Good headphone volume•Notorious for local RFinterference
Three Transistor Superregenerative Rx• T1 forms Colpitts RFoscilator•L1 and C1 form tunedcircuit•R1 and C5 form quenchcircuit and biassing•R2 is current sense resistor•T2 and T3 providedetection and AFamplification – signal “clean-up”•Audio or digital signals•This circuit forms basis ofmany modern SR receiversas used in doorbells, garageremotes, remote switchedsockets etc.
The Theory• Excellent Paper on designing Super Regenerative Receivers by Dr. Eddie Insam http://www.eix.co.uk/Articles/Radio/Welcome.htm• Thomas E. McEwan US Patent 5630216 http://www.freepatentsonline.com/5630216.html
Super-regenerative Rx used in doorbell•Inductor and capacitor intop left corner form tunedcircuit•Single regenerativetransistor below•1 transistor for detector•2 transistors foramplification and signalclean-up (squaring)•IC is doorbell melody chip•Runs on 3V at around1mA
Later SMT Super-regenerative Doorbell•Surface mount designfeaturing 6 transistors•Same basic regenerativecircuit•Four cascaded NPNtransistors used in “clean-up” chain.•Approx 35 parts but stillsignificantly <$1 toproduce
433MHz Laipac Super Regen Rx Module•Typical of a 433MHzmodule from severalmanufacturers.•Simple to use with industrystandard pin-out•Tuning capacitor, inductorand RF choke on back of pcb•Single regenerativetransistor stage followed byaudio amplifier•Clean-up and data slicingprovided by op-amp /comparator IC•Ideal for low data rates eg<4800 baud
Colpitts Oscillator – an RF building block•Forms the oscillator used in ASK, OOK transmitters and super-regen receivers•Single RF NPN transistor works well for sub 1GHz designs – ideal for 315MHzand 433MHz ISM / consumer applications•Frequency control can be added with surface acoustic wave resonator (SAW)•A complete transmitter circuit in a stamp sized module for <$1
Close-Up of 433MHz SAW Transmitter• SAW is large object in centre. T1 is RF transistor
Combine Low Power Wireless withMSP430 microcontroller•A simple design forremote controlapplications•Very low power MSP430•Runs on 2 xAA Cells•Charge pump produces 5Vto boost the RF amplitude– for longer range•Used to communicatewith a telephone modem(c2005) to send codedmessages back to server
These Tx and Rx circuits are so similar Can we make a low parts transceiver?Colpitts oscillator forms the basis of most OOK Colpitts oscillator used as regenerativetransmitter modules. stage of simple super-regen receiverNormally we would modulate the base currentto give amplitude modulation (ASK or OOK)Can we use external low frequency quenchoscillator to drive it in and out of RF oscillation?– Thus making a super-regenerative detector?
Yes we can!• Super regenerative transceiver – December 2009• Used Telecontrolli 433MHz SAW transmitter module – with external quench oscillator to drive it into super- regenerative mode• Received 1200 baud data
The 50uA Super-regenerative Transceiver December 2009 • Runs at 50uA from 1.5V cell • 1200 baud reception • Using microcontroller can be switched from Rx to Tx with a single port pin • Used 1:10 duty pulse waveform to run quench oscillator – more possibilities using analogue pwm • Ideal for room sized communications • Could be used as wake-up Rx for microcontroller and better Rx
Some WaveformsWe measure the current beingdrawn by the Colpitts oscillatorstage – with and without a sourceof RF present.1. Current Waveform into detectorwhen no RF signal present2. RF Signal presentCurrent pulse becomes longer –thus more energy consumed – andthis we can detect, amplify andclean up into a digital bit stream
Hacking a Lidl Power Socket for Internet control – SNAP RAT•A 1200 baud transmitter was connectedto a Microchip PIC Net dev kit•The RF protocol used was SNAP (ScalableNetwork Application Protocol) fromhth.com.•I had a low cost PIC with wireless design –called RAT – Remote Applications Terminal•The transmitter was driven from a PIC16F88 running SNAP•The super-regenerative receiver in theLidl remote control power socket was fine– just the decoding circuit sucked•So another PIC16F88 running SNAP wasused to intercept the packets, decodethem and activate the power switch•Simples
Conclusions• Super-regenerative receivers have their applications in low cost consumer gadgets where price sensitivity cannot support more than $1 build price.• They offer a route to micro-power receiver operation running for years from a single 1.5V cell• They can be used as wake-up receivers for more elaborate RF modules and microcontroller circuits• Very low RF power – ideal for room scale or near field communications or for low power wireless network nodes• Combined Tx and Rx operation is an exciting possibility for low cost bidirectional data nodes
Read More about Super Regen• Excellent Paper on designing Super Regenerative Receivers by Dr. Eddie Insam http://www.eix.co.uk/Articles/Radio/Welcome.htm• Thomas E. McEwan US Patent 5630216 http://www.freepatentsonline.com/5630216.html• The content of this presentation and these slides taken from my blog Nov/Dec 2009 http://sustburbia.blogspot.com/2009/12/wake-up-boo- 50ua-super-regenerative.html• Contact me: firstname.lastname@example.org @monsonite on twitter