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.com/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 regenerative circuit patented by Edwin Armstrong in 1914

•Disputed for 12 years by Lee De Forest

•One active element –a triode valve acting as RF oscillator/amplifier

•Very low parts count

•Easy for hobbyist to make

•Better sensitivity and selectivity than crystal set

•Good headphone volume

•Notorious for local RF interference

Three Transistor Superregenerative Rx• T1 forms Colpitts RF oscilator•L1 and C1 form tuned circuit•R1 and C5 form quench circuit and biassing•R2 is current sense resistor•T2 and T3 provide detection and AF amplification – signal “clean-up”•Audio or digital signals •This circuit forms basis of many modern SR receivers as used in doorbells, garage remotes, remote switched sockets etc.

The Theory

• Excellent Paper on designing Super Regenerative Receivers by Dr. Eddie Insamhttp://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 in top left corner form tuned circuit

•Single regenerative transistor below

•1 transistor for detector

•2 transistors for amplification and signal clean-up (squaring)

•IC is doorbell melody chip

•Runs on 3V at around 1mA

Later SMT Super-regenerative Doorbell

•Surface mount design featuring 6 transistors

•Same basic regenerative circuit

•Four cascaded NPN transistors used in “clean-up” chain.

•Approx 35 parts but still significantly <$1 to produce

433MHz Laipac Super Regen Rx Module

•Typical of a 433MHz module from several manufacturers.

•Simple to use with industry standard pin-out

•Tuning capacitor, inductor and RF choke on back of pcb

•Single regenerative transistor stage followed by audio amplifier

•Clean-up and data slicing provided 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 315MHz and 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

A Surface mount SAW resonator transmitter

Close-Up of 433MHz SAW Transmitter

• SAW is large object in centre. T1 is RF transistor

Combine Low Power Wireless with MSP430 microcontroller•A simple design for remote control applications

•Very low power MSP430

•Runs on 2 xAA Cells

•Charge pump produces 5V to boost the RF amplitude – for longer range

•Used to communicate with a telephone modem (c2005) to send coded messages 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 transmitter modules.

Normally we would modulate the base current to give amplitude modulation (ASK or OOK)

Can we use external low frequency quench oscillator to drive it in and out of RF oscillation? – Thus making a super-regenerative detector?

Colpitts oscillator used as regenerative stage of simple super-regen receiver

Yes we can!

• Super regenerative transceiver –December 2009

• Used Telecontrolli433MHz 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 being drawn by the Colpitts oscillator stage – with and without a source of RF present.

1. Current Waveform into detector when no RF signal present

2. RF Signal presentCurrent pulse becomes longer –thus more energy consumed – and this we can detect, amplify and clean up into a digital bit stream

300 baud and 1200 baud recovered data

• 300 baud

• 1200 baud

Hacking a Lidl Power Socket for Internet control – SNAP RAT

•A 1200 baud transmitter was connected to a Microchip PIC Net dev kit•The RF protocol used was SNAP (Scalable Network Application Protocol) from hth.com.•I had a low cost PIC with wireless design –called RAT – Remote Applications Terminal•The transmitter was driven from a PIC 16F88 running SNAP •The super-regenerative receiver in the Lidl remote control power socket was fine – just the decoding circuit sucked•So another PIC16F88 running SNAP was used to intercept the packets, decode them 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 Insamhttp://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: ken.boak@gmail.com @monsonite on twitter