Probe for diode-transistor logic. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Measuring technology
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Until now, industrial enterprises operate a large number of automation equipment with high-threshold diode-transistor logic chips (VPDTL) of the K511 series or Logic-I modules. And although this equipment is morally, and often physically, outdated, the task of maintaining its functioning remains relevant. As a rule, equipment developers did not introduce additional units to control and test the functioning of these devices, leaving this part of the work on the shoulders of the service personnel.
Faced with such a problem at one time, I developed a probe for monitoring the state of logical circuits and registering both single and series of pulses. This device is also protected against incorrect connection to the power supply and against accidental contact with the control probe of circuits with a voltage of 24 V and above, used to power electromagnets, relays, control lamps. Often this voltage is also applied to boards with logic microcircuits powered by 15V.
The probe circuit is shown in the figure.
The HL1 LED is designed to indicate voltages above +15 V (checking circuits with a voltage of +24 V). LEDs HL2, Hl-3 indicate the low and high logic levels of the signals, respectively. The counter on the DD2 chip counts the pulses received at the probe input, and the HL4 - HL7 LEDs indicate their number. With their simultaneous long-term glow, the DD2 chip heats up quite a lot, so after reading the information, you must press the S1 "Reset" button. In general, during long-term operation (more than 6 years) in harsh conditions, the device proved to be easy to use and reliable. The only inconvenience is that the device takes an unconnected control probe (and therefore an open circuit in the circuit under study) as a logical 1. However, in practice, the static state of the logical circuit is rarely taken into account. Much more informative is the change of logical states.
Structurally, the probe is made on a printed circuit board made of double-sided foil fiberglass 1,5 mm thick and inserted into a plastic case. Opposite the stem of the microswitch S1, a cone-shaped hole is made in the housing with a "funnel" outward to prevent the stem from breaking. As a probe, a sharpened piece of steel wire was used, inserted with force into the cut of the printed circuit board and soldered on both sides. The power wires going to the board end with crocodile clips at the ends for easy connection to the device under test.
Author: A. Stas, Rivne, Ukraine
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