Counters

The circuit in Figure 1 uses a regular, general-purpose transistor as the sensing element and a thermal-diode monitor IC to measure temperature. The ADM1021 usually connects to an on-chip thermal diode on a CPU die itself, but in this application the sensor connects to a regulator low-cost discrete npn transistor, the 2N3904. The circuit ties the transistor base and collector together to form a two-wire sensor...

There have been a lot of transistor tester circuits in recent electronics magazines, but this one is different. It has more features and includes a signal injector so you can test audio sections of radios and the front end of FM transmitters etc. The major advantage with this design is its automatic operation. All you have to do is fit the three leads of a transistor to the tester in any order and the LEDs will let you know the base and if the transistor is NPN or PNP...

It can be helpful to rapidly and easily determine the polarity (npn or pnp) and function of a transistor. The pocket-transistor tester in Figure 1 is ideal for quickly testing without regard to such parameters as gain and frequency response. You connect the transistor, or device under test, between the collectors, T, of an astable multivibrator. Thus, the VCE voltage of the device under test is alternately positive and negative...

A 13.56-MHz, ISM (industrial, scientific, and medical)-band RF-measurement device had the test requirement of a 50-hour, 1-kW burn-in. The device under test needed to be simultaneously stressed at an RF potential and RF current equivalent to 1 kW, but the only spare RF source at hand was a 100W RF generator. Besides, saving energy seemed important. The circuit in Figure 1 develops 1 kW from the 100W RF source by storing energy in a transmission line...

When you connect remote sensors to a central process controller, a simple, robust, and commonly used interface is the 4- to 20-mA loop. The advantages of this current loop include the simplicity of just two twisted wires that share both power and signal, the loop`s high noise immunity in harsh environments, and the de facto loop standard within the process-control industry...

An old technique updated for modern requirements allows you to measure all three line currents in a three-phase system. You perform this measurement using two current transformers (CTs) and three ammeters. The original technique appeared in Alternating-Current Machines by George Mueller (McGraw-Hill, 1952)...

This circuit is not a novelty, but it proved so useful, simple and cheap that it is worth building. When the positive (Red) probe is connected to a DC positive voltage and the Black probe to the negative, the Red LED will illuminate. Reversing polarities the Green LED will illuminate. Connecting the probes to an AC source both LEDs will go on. The bulb limits the LEDs current to 40mA @ 220V AC and its filament starts illuminating from about 30V, shining more brightly as voltage increases...

A simple circuit (Figure 1) and accompanying software turn a pressure sensor into an accurate and cheap pressure digitizer that works with any PC`s RS-232C COM port. Many manufacturers make micromachined silicon piezoresistive pressure sensors. Sensors are available with full-scale sensitivities ranging from inches of water to hundreds of pounds per square inch...

A remote data-acquisition circuit for monitoring a patient`s vital signs--pulse rate, respiration, and temperature--uses very little power as well as inexpensive sensors and circuits (Figure 1). The data-acquisition portion uses the low-cost CD4000 series of CMOS ICs and consumes less than 50 mA from a 3V battery. The circuit uses 50x oversampled sigma-delta ADCs with a PWM/FM system, which combines three data channels on one RF carrier...

Here is a handy zener diode tester which tests zener diodes with breakdown voltages extending up to 120 volts. The main advantage of this circuit is that it works with a voltage as low as 6V DC and consumes less than 8 mA current. The circuit can be fitted in a 9V battery box. Two-third of the box may be used for four 1.5V batteries and the remaining one-third is sufficient for accommodating this circuit...

This Design Idea describes a versatile test circuit for zener diodes after yet another misread zener diode had infiltrated the ranks of 1N4148 diodes assembled on a pc board. As a bonus, the circuit can serve as a moderate-voltage, power-limited adjustable dc source. Although conventional multimeters` resistance ranges typically apply enough voltage to forward-bias most diodes, few can drive a zener diode into reverse conduction...