Capt. Rhys-James - electronic circuits

radio circuit fragment

The science teacher at my middle school (Broadwater Manor, Worthing) was Capt. David Rhys-James (died 2013, aged 91). He was an excellent science teacher and was also very keen on electronics and inspired many of us to experiment and build electronic projects for ourselves. He devised a few excellent circuits for us to make at home (or during science club after school). For someone like me (dyslexic, reading and writing difficulties etc.) they made all the difference, making school really inspiring. He was a very tall and imposing figure, with has pipe in hand was a bit like the Lord of the Rings wizard! He was a thoughtful man and if you asked him a question he would pause, knock his pipe against the side of the table, fill it with tobacco light it and blow out clouds of smoke and then would often give you an inspiring answer ! His science lab seemed to me to be full of magic constructions of his own devising; built with real skill. He had one of the first UK101 6502 computer kits which he had built and constructed in a beautifully made matallic paint sprayed box.

He made up 1-page A4 designs so you had everything you needed to know on one piece of paper. This included the circuit diagram, a Vero board (strip-board) layout, sometimes a short description of what the circuit did and how it worked along with a few notes on any critical voltages that might be measured to aid construction. A few have survived in my collection from the late 1970's early 1980's and I have a link to a scan of each one here (see PDF links below):

BERNI - Binary Electric Random Number Indicator
This circuit uses two transistors in a flip-flop configuration to rapidly alternate the flashing of two LEDs. Powered by a 9V PP3 battery. The oscillator runs at a few. 10's kHz and can be stopped at any time using a push button, revealing which transistor (and LED) happened to be ON at the time the switch was pressed. As human reaction times are relatively imprecise the particular LED that remains lit , from one push of the button to another is basically random - like flipping an electric coin. The timing resistors (15k ohm) and capacitors (0.01 uF) should be matched as closely as possible so that the flip-flop mark-space ratio will be close to 50:50 so that one LED is not biased ON more than the other. When you turn on the unit the LEDs are both on (flashing very fast) and when you press the push switch which ever LED was on at that moment stays on. As it's 50:50 which will be on, you can mark one LED with 'heads' or '0' and the other with 'tails' or '1' to electronically flip the coin or generate random digits.

ZN414 medium wave radio
This circuit uses the transistor style 3-pin ZN414 radio IC to make a tiny medium wave radio (note the ZN414 has now been replaced by the MK414 but the original can still sometimes be found on e-bay etc.). It runs on 1.5V so it can run from a AA or AAA battery. It was very exciting to get the radio working - a real 'peak' experience for me. In the 1970's and 80's there was a lot more interesting stations to listen to on the medium wave too!

LED flasher (9 V)
This two transistor oscillator circuit flashes an LED to give a nice short burst of bright light from an LED. It runs on 6-9 V. This circuit was a big step forward for me as I came up with my own Vero board layout before the teacher (or anyone else) created one. So I was able to bring in the circuit working by my own industry and skill which really boosted my confidence (I was 11 at the time, 1979).

LM3909 LED flasher (1.5 V)
I am not sure if Capt. Rhys ever drew up a Vero-board layout of this circuit but he definitely introduced the chip to me. This classic circuit flashes an LED using only a 1.5V battery. An LED needs more voltage to light than a AA or AAA battery can provide, so this clever circuit voltage doubles by storing 1.5V across a capacitor and then add it in series with the battery to create a short 3V pulse, or burst of higher voltage able to light the LED. One version of this circuit I have has run on a D-type cell for over 11 years continuously, which is longer than some of the participants in my younger classes have been alive ... in this case the LED has been pulsing for longer than their hearts have been beating!


BERNI ZN414
radio
LED
flasher
LED
flasher
(my version)
LM3909
flasher
(my version)



THE CREATIVE SCIENCE CENTRE

Dr Jonathan Hare, The University of Sussex
Brighton, East Sussex. BN1 9QJ.

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