Video Pick Off Circuit
Original Publication Date: 1981-Oct-01
Included in the Prior Art Database: 2005-Feb-12
This circuit accepts dot-form video signals from a CRT display and converts them to a form suitable for driving a dot-type printer. The video signals are taken from the analog beam intensity input to the display CRT. Thus, it is desired that only a minimal current be drawn from the analog signal to avoid degrading the CRT's performance. Moreover, in some CRT displays, this signal is an on/off signal providing pulses of a nominal intensity spaced apart on a 50% duty cycle to display a row of dots at normal intensity, and pulses of higher amplitude and longer duration to display bold-face characters. For example, nominal pulses may be 35 ns long recurrent (where a row of dots is to be displayed) at 70 ns intervals, producing a 50% on/off signal of a first amplitude.