Presented at #C4CC OSHUG #15 meeting - Jan 26th 2012

1. Radio Days – 40 Years of
Experimental Wireless
From Crystal Sets to CC1110s
– and everything in between.
Ken Boak OSHUG C4CC 26th January 2012

2. 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

3. 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!

4. 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

5. 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

6. 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

7. 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.

8. 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

9. 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

10. 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

11. 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

12. 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

13. A Surface mount SAW resonator transmitter

14. Close-Up of 433MHz SAW Transmitter
• SAW is large object in centre. T1 is RF transistor

15. 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

16. 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 regenerative
transmitter modules. stage of simple super-regen receiver
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?

17. 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

18. 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

19. Some Waveforms
We 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 present
Current pulse becomes longer –
thus more energy consumed – and
this we can detect, amplify and
clean up into a digital bit stream

20. 300 baud and 1200 baud recovered data
• 300 baud
• 1200 baud

21. 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

22. 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

23. 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: ken.boak@gmail.com @monsonite on twitter