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A Circuit to Convert Random Pulses into Uniform Pulses

Author: J.B. Hoag

The left half of the circuit of Fig. 30 I will convert random pulses of from 30 to 3,000 counts per minute into pulses of uniform length and amplitude.

Fig. 30 I. A circuit to convert random pulses into uniform pulses. Also, a frequency meter. (See Rev. Sci. Inst., Dec. 1936)

It is basically a multivibrator, but possesses one marked difference from the usual form of this circuit; namely, that the grid of tube 1 (part of a 6N7 tube) is biased negatively beyond cutoff, whereas the grid of tube 2 is at the more usual zero bias voltage. This is accomplished by passing current from the B supply through R1 via the 50,000-ohm resistor. Thus, at the start, 1 is off and 2 is on. A positive pulse on the grid of 1 trips this tube, current flows through R2, reducing the voltage on the plate of 1. This sends a negative pulse through C2 onto the grid of the tube 2. The plate current through 2 is thereby reduced and its plate voltage increased. This positive pulse passes through C3 to the grid of 1, augmenting the original input pulse. The interaction continues until the plate voltage on 1 is very small. The circuit remains in this condition until the charge on C2 leaks to the cathode through R4. When the grid of 2 reaches a certain critieal voltage, the entire process reverses itself to restore the original conditions (1 off and 2 on).

Thus an input pulse of any size or duration (within limits) initiates a series of events wherein 2 is turned off and then back on again sharply after a definite time interval determined by the circuit constants and not by the input pulse. The resultant potential variations across R3, and across the output terminals shown in Fig. 30 I, are of square wave-form.

Last Update: 2009-11-01