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Index 42

Simple Electronic Keyer

Published:2012/12/6 19:45:00 Author:muriel | Keyword: Simple Electronic Keyer

Simple Electronic Keyer
A simple keyer suitable for a popcorn QRP transmitter can be built around an astable multivibrator and an example of such is shown above. The basic design of this keyer is from notes, however the original author of the circuit is unknown. The notes were written in 1973 . I modernized the circuit, added a variable speed control and designed an additional output driver stage. Keying this circuit generates either dits and spaces or dahs and spaces. When the keyer is idle, Q1 is on and Q2 and Q3 are switched off. When the user sends code, Q1 turns off and Q2 and Q3 switch on and in turn key any device appropriately connected to the collector of Q3. The off-time of Q1 sets the on-time of Q2 and Q3. The off-time of Q2 and Q3 is set by the 22K Q2 base resistor. This off-time is the set time of the spaces and is constant. The 68K resistor on the base of Q1 is about three times the resistance of the 22K base resistor on Q2 and consequently dahs are ~ three times the length in duration than dits. Spaces and dits are of the same length of time because when sending dits, the 68K base resistor is paralleled with the 33K resistor and effectively the resistance is ~22K ohms. If the optional relay driver transistor Q4 is used instead of Q3, the theory is the same, just substitute Q4 wherever you see Q3. (View)

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3-wire serial LCD interface

Published:2012/12/6 1:16:00 Author:muriel | Keyword: 3-wire, serial, LCD interface

3-wire serial LCD interface
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Period timer for aquarium, sprinklers and more

Published:2012/12/6 1:16:00 Author:muriel | Keyword: Period timer, aquarium, sprinklers

Period timer for aquarium, sprinklers and more
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Dual light timer

Published:2012/12/6 1:14:00 Author:muriel | Keyword: Dual light timer

Dual light timer
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LCD thermometer

Published:2012/12/6 1:13:00 Author:muriel | Keyword: LCD thermometer

LCD thermometer
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Electronic combination lock

Published:2012/12/6 1:12:00 Author:muriel | Keyword: Electronic combination lock

Electronic combination lock
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Repeating Timer No.8

Published:2012/12/5 0:09:00 Author:muriel | Keyword: Repeating Timer

Repeating Timer No.8
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Repeating Timer No.7

Published:2012/12/5 0:09:00 Author:muriel | Keyword: Repeating Timer

Repeating Timer No.7
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24 Second Shot Clock Mk 2

Published:2012/12/5 0:08:00 Author:muriel | Keyword: 24 Second, Shot Clock Mk

24 Second Shot Clock Mk 2
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741 Astable Timer

Published:2012/12/5 0:07:00 Author:muriel | Keyword: 741 Astable Timer

741 Astable Timer
An astable timing circuit made from the ubiquitous 741 op-amp. (View)

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Sequential Timer

Published:2012/12/5 0:06:00 Author:muriel | Keyword: Sequential Timer

Sequential Timer
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1 Hour Timer

Published:2012/12/5 0:06:00 Author:muriel | Keyword: 1 Hour, Timer

1 Hour Timer
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Repeating Timer No.2

Published:2012/12/5 0:05:00 Author:muriel | Keyword: Repeating Timer

Repeating Timer No.2
This circuit is based on a simple asymmetric oscillator. The length of time the relay remains energized - and the length of time it remains de-energized - are set independently. With the component values shown in the diagram - both periods are adjustable from about 1 to 30 minutes. (View)

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Repeating Interval Timer

Published:2012/12/5 0:04:00 Author:muriel | Keyword: Repeating Interval Timer

Repeating Interval Timer
This circuit has an adjustable output timer that will re-trigger at regular intervals. The output period can be anything from a fraction of a second to half-an-hour or more - and it can be made to recur at regular intervals of anything from seconds to days and beyond. (View)