## Delay Circuitry In the circuit above, when key A is pressed, electromagnet B is powered and key B closes. It takes time for B to close after A is pressed. That is, light B comes on about one hundredth of a second after light A. This is indicated by the following 'timing diagram' that shows when the lights come on. Time 0 is 0 seconds. Time 1 is one hundredth of a second (later).

## Timing Diagram for Lights ## Two Delays In the circuit above, after key A is pressed it takes one hundredth of a second for key B to close. After key B closes, it takes one hundredth of a second for key C to close. Therefore, after key A is pressed, it takes two hundredths of a second for light C to come on. In the following timing diagram for the circuit above, time 0 is 0 seconds, time 1 is one hundredth of a second, and time 2 is two hundredths of a second.

## Timing Diagram for Lights ## Delay Line In the circuit (called a delay line) above, light B comes on ten hundredths of a second after light A. Ten hundredths of a second is one tenth of a second, so light B comes on one tenth of a second after key A is pressed (as indicated in the diagram below). (The small amount of time between the time key A is pressed and the time light A comes on is ignored.) Time 0 is 0 seconds and time 1 is one tenth of a second in the diagram below.

(When a key closes, it can bounce open and closed a few times. This possible problem will be ignored, except to say that using normally closed relays in a delay line might reduce the problem. This problem does not exist in a delay line made with transistors.)

## Timing Diagram for Delay Line ## Tapped Delay Line The circuit above is called a tapped delay line. Wires A, B, C, D, and E are called taps. Light B comes on one tenth of a second after light A, light C comes on two tenths of a second after light A, light D comes on three tenths of a second after light A, and light E comes on four tenths of a second after light A (as indicated in the timing diagram below).

## Timing Diagram for Tapped Delay Line Page 20

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