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Fig* 1BW See text.

frequency counter depending oil the position of the display time switch. In this design the display time is one, two and four seconds, The actual display time is the time selected hy the display time switch less a two-pulse time selected by the time base switch. As an example assume the time base switch is set on 1KC (1 millisecond) and the display time is 1 second, The count will be for one millisecond and the display for 999 milliseconds, This is very close to the time selected by the display time switch, but if the count is for one second as would be used to count very low audio frequencies then the display time switch should be set for either two or four second display for a reading because in the one second display time position the counter will count for one second and then immediately reset at the end of one second period, resulting in a continuous count and no display time for readout.

Persons interested in building the complete counter or only part of the circuit should start with the basic counter module of Fig, 6, which can be expanded to as many flip-flops and lamps as needed for other applications.

The average toggle or push button switch is too noisy for this application so one should to use one to control the basic counter module. The one shot portion of the gate lamp circuitry of Fig. XI is shown in Fig. 1.2 and should be used in place of the switch to drive the basic counter module.

The standard coding used on the mL 900, mL 914 and ^L 923 is that pin 4 is ground and pin 8 goes to +3,6 V. On the mL 926 pin 5 is ground and pin 10 goes to +3.6 V.

Another point to remember is that all unused input pins must be grounded for noise immunity. As a point to remember it should be noted that all pin numbering is done from the top. Remember when working from the bottom of the board they are still numbered like the tubes we are familiar with.

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