Meters Circuits

Undervoltage indicator for battery equipment

Due to the low duty cycle of flashing LED, the average current drain is 1 mA or less. The NE555 will trigger the LED on when the monitored voltage falls to 12 volts..

Remote Field Strength Meter Circuit

This field strength meter consists of a tuned crystal detector producing a dc output voltage from a transmitted signal. The dc voltage is used to shift the frequency of a transmitter of 100-mW power operating at 1650 kHz. The frequency shift is proportional to the received field strength...

Little dipper

The circuit consists of two basic circuits, the oscillator and the detector. The oscillator uses an FET in a Colpitts configuration. The energy circulating in the oscillator tank is coupled through C4 to the detector circuit, where a small diode (D2) rectifies it, feeding a dc voltage to the Darlington pair (Q2, A3) controlled by the sensitivity control (R3). Any small variations in the bias of the amplifier will cause large variations of current through the LED indicator.....

Line-current-monitor

A low-cost filament transformer provides a linear indication of the load current in an ac line. ..

Digitizer

If the tube is level with respect to gravity, the bubble resides in the tube"s center and the electrode resistances to common are identical. As the tube shifts away from level, the resistances increase and decrease proportionally. Transducers of this type must be excited with an ac waveform to avoid damage to the partially conductive liquid inside the tube. The level transducer is configured with a pair of 2-KO resistors to form a bridge. The required ac bridge.....

Sample-and-hold

The sample-and-hold function has often been accomplished with separate analog switches and op amps. These designs always involve performance tradeoffs between acquisition time, charge injection, and droop rate. The HA-242-/2425 monolithic sample-and-hold. ..

Guarded input picoammeter circuit

The circuit utilizes CA3160 and CA3140 BiMOS op amps to provide a full-scale meter deflection of Â± 3 pA. The CA3140 serves as an 1T0 gain stage to provide the required plus and minus output swing for the meter and feedback network. ..

Oscilloscope Preamplifier Circuit

An oscilloscope front-rend amplifier can be built with low-cost transistor and video amp ICs. This preamp uses a FET input and compensated attenuators, and has approximately 100-MHz bandwidth,..

Filtered-sample-and-hold

Itis often required that a signal be filtered prior to sampling. This can be accomplished with only one device. Use any of the inverting and noninverting filters that can be built with op amps. ..

Nanoampere sensing circuit

The circuit may be used as a sensitive current detector or as a voltage detector having high input impedance. Rl is set so that the voltage at point (A) is V2 to % volts below the level that fires the 2N494C. A small input current (Iin) of only 40 nanoamperes will charge C2 and raise the voltage at the emitter to the firing level..

Sample-and-hold

The LM101A provides gain and buffers the input from storage capacitor C2. R2 adds a zero in the open loop response to compensate for the pole caused by the switch resistance and C2, improving the closed-loop stability. R1 provides a slight delay in the digital drive to pins 1 and 9. C1 provides cancellation of coupled charge, keeping the sample-and-hold offset below 5 mV over the analog signal range of -10 through +10 V. ..

Modulation monitor

Broad-tuned receiver demodulates the RF signal picked up by a ioosely coupled wire..

Tachometer-and-direction-of-rotation-circuit

In machine and equipment design. some applications require measurement of both the shaft speed and the direction of rotation. Fig. 56-4 shows the circuit of a tachometer, which also indicates the direction of rotation. The flywheel has two magnets embedded in the outer rim about 45Â° apart. One magnet has the north pole toward the outside and the other magnet has the south pole toward the outside rim of the flywheel. ..

Sample and hold

The 2N4393 JFET was selected because of its low less (< 100 pA), very low ID (< 100 pA) and low pinchoff voltage..

Sample-and-hold

This circuit uses a CA3140 BiMOS op amp as the readout amplifier for the storage capacitor Cl, and a CA3080A variable op amp as input buffer amplifier and low feedthrough transmission switch. ..

Signal-Strength Meter

This field-strength meter is useful for antenna testing. It covers 6 to 60 MHz and uses a rugged 0-to-l mA meter. A 9..

Electrolytic Capacitor Reforming Circuit

Sometimes electrolytic capacitors that are stored for some time will exhibit high leakage currents..

Diode tester

The circuit will display curves on a scope, contingent on the state of the diode. To ' 'calibrate,'' substitute a 1000-ohm resistor for the diode and adjust the scope gains for a 45-degree line. ..

Shutter-speed tester

The solar cell is connected across the input of the FET (field-effect transistor), Ql, so that it will produce positive dc voltage to the gate when activated by light shining through the open shutter, decreasing the negative gate-source bias already established by the source resistor, and causes an increase in drain current. The drain voltage goes more negative which causes a decrease in Q2's base current. Q2's collector current decreases, and its collector voltage becomes.....

Ratiometric resistance measurement

The unknown resistance is put in series with a known standard and a current passed through the pair. The voltage developed across the unknown is applied to the input and the voltage across the known resistor applied to the reference input..