AC-DC Microammeter Circuit

Here’s a design circuit that is used to active circuitry and an analog meter to make sensitive DC current measurements. A reader subsequently asked if it could measure AC microamperes and that is what spawned the idea. This is the figure of the circuit;

While the schematic is similar, there are notable differences—the voltage drop is now 100mV rather than 1V, the sensitivity is 10nA full scale rather than 100nA and it now measures AC or DC. A precision rectifier rectifies the AC voltage so that a DC meter may be used. Actually, this is wishful thinking because the sensitivity is too great for my set-up. As a result, the meter reads half-scale (5nA AC noise) without anything connected. The 100nA setting is much more reasonable—Mr. Marian obviously knew what he was doing by limiting his circuit to 100nA FS. 10nA can still be measured, but the meter would be reading 10% deflection on the 100nA range. All would work better if packaged inside a shielded enclosure. On the 10nA range, it is so sensitive that AC current caused by body capacitance at a distance of 30mm from the input lead was easily visible—something like putting your hand near a high impedance oscilloscope probe and watching the AC pickup on the trace.

Blood Pressure Measurement Circuit

This is a design circuit for inside this technical document we can get info like augmentation procedures, position, gauge, pressure, maximum inflation, circulation, systolic pressure, blood pressure, and cuff. There are lots of info regarding blood, maximum inflation level, brachial artery, cardiovascular health, health, stethoscope, deflation, artery, and sound are described inside this technical document. This is the figure of the circuit; 

This technical document gives us discussion about rate, diastolic, aneroid, reading, inflation level, systolic, korotkoff, estimated systolic pressure, and measurement. Additionally, the technical document explains discussion such as estimated systolic, bladder, diastolic readings, inflation, diaphragm, korotkoff sounds, procedure, korotkoff phase, and pulse.

R/tC Servo Tester Circuit

Here’ s a design circuit for servo signal is a simple digital pulse. It spends most of its time at a logic low (0 V). About every 20mS it goes logic high (3 to 6 VDC) and then quickly goes low again. It is this tiny window of logic high time, called the pulse width, that gets the attention of the servo. Here’s the figure of the circuit;

Please refer to the drawing. The period labeled "A" is called the frame rate. In the example it is repeated every 20mS (50 times per second), which is quite typical for most radio systems. Modern servos define center as a 1.5mS pulse width, as shown by detail "B" in the drawing. Full servo rotation to one side would require that this pulse width be reduced to 1.0mS. Full rotation to the other side would require the pulse width to increase to 2.0mS. Any pulse width value between 1.0mS and 2.0mS creates a proportional servo wheel position within the two extremes. The frame rate does not need to change and is usually kept constant.

 

The servo will not move to its final destination with just one pulse. The servo amp designers had brilliantly considered that multiple pulses should be used to complete the journey. This little trick reduces servo motor current draw and it helps minimize erratic behavior when an occasional corrupt signal is received. To move the servo, you must repeat the pulse every few milliseconds, at the chosen frame rate. Modern R/C systems use a 40Hz - 60Hz frame rate, but the exact timing is not critical. If your frame rate is too slow, your servo's movement will become rough. If the rate is too fast the servo may become very confused.

AC Ohmmeter - ESR Meter Circuit

The ESR Meter is basically an AC Ohmmeter with special scales and protective circuitry. It provides a continuous reading of series resistance in electrolytic capacitors. It operates at 100 kHz to keep the capacitive reactance factor near zero. Here’s the figure of the one design circuit for ESR meter circuit;

The ESR meter uses 8 operational amplifiers. An op-amp is an idealized basic amplifier with two inputs. The non-inverting input (+) has an in-phase relationship with the op-amp output, and the inverting input (-) an out-of-phase relationship. Op-amps are usually used with negative feedback and reach a stable operating condition when their two inputs are equal in voltage. Op-amps IA & 1B form a regenerative 100 kHz oscillator circuit. Capacitor C1 is the basic timing capacitor and RI is selected to set frequency. Diodes D2 & D3 clip the bottom and top of the output waveform so that the output level and frequency are resistant to battery voltage changes.

The oscillator output of op-amp 1B drives 10-ohm source resistor R8F. The test-capacitor, thru the test leads, couples this 100 kHz signal to 10-ohm load resistor R9F. The amount of voltage developed here is indicative of the capacitors ESR value. (The 10-ohm resistors determine the basic meter scaling.) Capacitor C3 blocks any DC voltage present on the test-capacitor. Diodes D4 & D5 protect the ESR Meter from any initial charging current to C3. Resistor R7 discharges C3 after test. A DC operating bias of 0.55 V is established by diode D1 for the oscillator stage and for all subsequent stages, which are DC coupled and operated class A. DC bias from D1 and ESR signal from R9F are combined at the input of op-amp 1D. Both voltages are amplified by 1D, 1C, & 2A. Each of these three stages has an amplification factor of about 2.8 due to the ratio of output-voltage to feed back voltage at the (-) input, which is determined -by feedback resistors R13F & R14F, etc.

Audio Power Meter: Shows Your Audio Amplifier’s Actual Output Power

This is a circuit that can be used to measure the actual output power of your amplifier. You can put this circuit in a box as a measurement instrument, or you can integrate it inside your power amplifier to get real power display. This is the figure of the circuit;

 

This  circuit would be a handy instrument for audio engineer, for field testing and checking of sound system installations. Because the scale is logarithmic, you can measure wide range of audio output with only ten scales.  Look at the pin 5 of the LM3915, you can see that the input is not rectified. The negative swing will present at this input pin, but it harmless because the current is limited by R1, and the LM3915 will respond to positive cycle only.

The absence of peak detector or average detector will give the circuit a fast reading of instantenous power, and this gives us insight of both average and peak condition. For more readable peak or average measurement, you can use peak or average detector circuit. [Circuit diagram source: National Semiconductor Applicataion Notes]

Ultrasonic Measurement Circuit Using Electrostatic Transducer

This is a design circuit for an electrostatic transducer for ultrasonic measurement circuit. This circuit uses the LM1812 ultrasonic transceiver. Transducer x1 and LM1812 will transmit a burst of oscillations. Then  the return echo is listened by using X1. The LM1812 detector will generate a pulse of the same width as the original burst when the X1 receive an echo of sufficient amplitude. If the return echo is early, it’s mean the object is near. This is the figure of the circuit;

If the parts and values shown are used, this circuit has a range of about 4 inches to 30 feet. The X1 has a 500-pF capacitance that resonate with the L6 at 50 to 60kHz. The L1 is tuned to this frequency by watching for maximum echo sensitivity with a scope at pin 1. [Circuit diagram source: National Semiconductor Linear Application]

Multi Wire Cable Tester Circuit

This is a circuit for multi wire cable tester with a separate LED for each wire. Will show open circuits, short circuits, reversals, earth faults, continuity and all with four IC's. Designed initially for my intercom, but can be used with alarm wiring, CAT 5 cables and more. This is the figure of the circuit;

The circuit comprises transmitter and receiver, the cable under test linking the two. The transmitter is nothing more than a "LED chaser" the 4011 IC is wired as astable and clocks a 4017 decade counter divider. The 4017 is arranged so that on the 9th pulse, the count is reset. Each LED will light sequentially from LED 1 to LED 8 then back to LED 1 etc. As the 4017 has limited driving capabilities, then each output is buffered by a 4050. This provides sufficient current boost for long cables and the transmitter and receiver LED's. The receiver is simply 8 LED's with a common wire.

Network Lead Tester Circuit

This is a circuit for confirming the continuity and correct wiring of computer network leads which have 8 wires, but it can be used to check any lead with up to 8 wires by using appropriate connectors. For example stereo audio leads with 5-pin DIN plugs can be checked by just using the first 5 LEDs. The tester is simple but it can save a great deal of time when making up leads and it is much cheaper than the more sophisticated alternatives. This is the figure of the circuit;

The tester works by connecting each wire to an output at one end and an LED at the other end. The outputs are switched on one at a time in sequence so that a correctly wired lead will make each LED light in turn. The 4017 IC counts up to 10 so there is a pause (for the 9th and 10th counts) before the LED sequence repeats. If the LEDs light up in the wrong sequence one (or both) of the connectors is wired wrongly. If an LED fails to light it indicates a broken connection. Please note that the RJ45 computer network plugs cannot normally be re-wired, instead they must be cut off and replaced.

Cell Phone Battery Meter Circuit 3.6 Volt

This is a circuit for charger that is is a similar circuit to the above and provides a 4 LED bar graph indicating the voltage of a common 3.6 volt Lithium – Ion recharable cell phone battery. The reference voltage is provided by a TL431 programmable voltage source which is set to 3.9 volts where the TL431 connects to the 1K resistor. The lower reference for the LED at pin 14 is set with the 5K adjustable resistor. This is the figure of the circuit;

The programmed voltage of the TL431 is worked out with a voltage divider (10K 5.6K). The adjustment terminal or junction of the two resistors is always 2.5 volts. So, if we use a 10K resistor from the adjustment terminal to ground, the resistor current will be 2.5/10000 = 250uA. This same current flows through the upper resistor (5.6K) and produces a voltage drop of .00025 * 5600 = 1.4 volts. So the shunt regulated output voltage at the cathode of the TL431 will be 2.5 + 1.4, or 3.9 volts.

Working out the LED voltages, there are three 390 ohm resistors in series with another adjustable (5K) resistor at the bottom. Assuming the bottom resistor is set to 2K ohms, the total resistance is 390+390+390+2000 = 3170 ohms. So, the resistor current is the reference voltage (3.9) divided by the total resistance, or about 3.9/ (390 + 390 + 390 + 2000) equals 1.23 mA. This gives us about .00123*2000= 2.46 volts for the bottom LED, and about .00123*390 = .48 volts for each step above the bottom. So, the LEDs should light at steps of 2.46, 2.94, 3.42, and 3.9. A fully charged cell phone battery is about 4.2 volts. You can adjust the 5.6K resistor to set the top voltage higher or lower, and adjust the lower 5K resistor to set the bottom LED for the lowest voltage. But you do need a 6 to 12 volt or greater battery to power the circuit.

Water Level Controller Circuit

This is a design circuit for water level controller circuit that described here control the water level inside a tank. There two modes available with this water level controller circuit. The first mode is empty mode, when the controller will drain the tank if the water level reach the upper limit, the pump will be used to suck the water from the tank until the water level drop below the lower level. The second mode of this water level controller is fill mode. Here the pump will be used to fill the tank with the water when the water level is drop below the lower limit, the pump will be activated until the water level reach the upper limit. This is the figure of the circuit;

The circuit is use NOR logic gates, only one IC package and one transistor is needed for the active components, very simple design. The default position of  push SW1 (as shown in the schematic diagram) is empty mode, just switch to other position to make the water level controller works in fill mode operation.  The relay can be used to control almost any type of water pump motors. Please be aware that this circuit works only with water or other electrically conductive liquids.

Noise Floor Measurement Circuit of PLL Frequency Synthesizers

Phase noise is a critical performance parameter of frequency synthesizers for wireless applications. RF system designers of phase modulated cellular systems, such as PHS, GSM and IS-54, need low noise local oscillator (L.O.) or frequency synthesizer blocks. This is a design circuit for the measurement system. This is the figure of the circuit;

The basic phase-lock-loop configuration we will be considering in the figure. The PLL consists of a high-stability crystal reference oscillator, a frequency synthesizer such as the National Semiconductor LMX2332TM, a voltage controlled oscillator (VCO), and a passive loop filter. The crystal reference used is the 10 MHz signal from the back of a spectrum analyzer at about +7 dBm or 1.42 VPP. The VCO used for this test was an ALPS URAE8x934 VCO with a tuning constant of 27 MHz/V phase locked at 900 MHz. By using a relatively wide loop filter bandwidth, (15 kHz for N = 4500) we are able to vary the reference frequency from 30 kHz to 400 kHz without changing the component values and maintain loop stability. The phase noise measurements were made at 150 Hz offset, to ensure that the data was on the flat portion of the curve “inside the loop”. At least 20 video averages were taken over a 1 kHz span for each measurement. In order to come up with the phase noise floor figure of merit the spectrum analyzer measurement must be normalized in terms of dBc/Hz, by subtracting 10 log of the resolution bandwidth used in the measurement. The noise is then referenced to the input of the phase detector by subtracting 20 log N.

[Circuit source: National Semiconductor Notes]

Thermocouple Gauge Principle Operation

The thermocouple gauge uses the thermal conductivity property of gases, by incorporating a wire filament which is heated by a constant source of power. Attached to this filament is a thermocouple, which measures the temperature of the wire. At high pressures, the large number of gas molecules striking the heated wire carries energy away and cools the wire. At low pressures, the smaller number of gas molecules striking the wire causes less cooling, and thus a higher temperature. This is the figure of the principle operation of the theory;

The thermocouple output voltage responds to these temperature changes to give an indication of pressure: low gas pressure gives high filament temperature which gives high thermocouple output voltage; high gas pressure gives low filament temperature which gives low thermocouple output voltage. The meter measuring the thermocouple voltage is calibrated in pressure units to give a direct indication of pressure. At pressures below about 10-3 torr, the heat loss from the filament is primarily through radiation since the density of gas molecules is so low. Since the heat loss due to radiation is constant, the resulting temperature corresponds to the “zero” reading on the meter. The thermocouple gauge is a simple, rugged device which is very useful at rough vacuum pressures. The meter covers the pressure range of 1 to 2000 millitorr. This is the schematic diagram of the thermocouple circuit.

[Schematic source: Duniway Stockroom Corp.]

Zener Diode Tester Circuit

This is a circuit for 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. In this circuit a commonly available transformer with 230V AC primary to 9-0-9V, 500mA secondary is used in reverse to achieve higher AC voltage across 230V AC terminals. This is the figure of the circuit.

Transistor T1 (BC547) is configured as an oscillator and driver to obtain required AC voltage across transformers 230V AC terminals. This AC voltage is converted to DC by diode D1 and filter capacitor C2 and is used to test the zener diodes. R3 is used as a seri-es current limiting resistor. After assembling the circuit, check DC voltage across points A and B without connecting any zener diode. Now switch on S1. The DC voltage across A-B should vary from 10V to 120V by adjusting potentiometer VR1 (10k). If every thing is all right, the circuit is ready for use. For testing a zener diode of unknown value, connect it across points A and B with cathode towards A. Adjust potentiometer VR1 so as to obtain the maximum DC voltage across A and B. Note down this zener value corresponding to DC voltage reading on the digital multi meter. When testing zener diode of value less than 3.3V, the meter shows less voltage instead of the actual zener value. However, correct reading is obtained for zener diodes of value above 5.8V with a tolerance of 10per cent. In case zener diode shorts, the multi meter shows 0 volts

Programmable Pressure Transducer

This circuit is design allows only a small diaphragm deflection sin it has limited elasticity, and this produces only a very small output signal, only about 1% modulation of the bridge resistance elements. This circuit is based on LM4041. This is the figure of the circuit.

The A2 circuit provides for the precision adjustment, via DCP1, of any transducer initial null offset error. To accomplish this, the bridge excitation voltage is programmable attenuated by the R2, R3, R4, R5 network and applied to DCP1. Boosting the ~10mV/psi bridge signal by 100x to a convenient 1V/psi output level is the job of the A3 non-inverting amplifier via its feedback and calibration network consisting of R7 through R9 and DCP2. The range for the zero adjustment voltage is from +22mV to –22mV. The resolution is 172uV and is proportional to the bridge excitation voltage, thus improving the temperature stability of the zero adjustment.

The net result of the combination of transducer and the Figure 4 circuitry is a signal conditioned precision pressure sensor that is compatible (thanks to DCP1 and 2) with full automation of the calibration process, is very low in total power draw (< 1 milli ampere, most of which goes to transducer excitation), and (equally important) is low in cost.

Dazzling Intensity Circuit in Light a White LED

This is a circuit that is used as indicators or to provide illumination, LEDs are hard to beat in efficiency, reliability, and cost. White LEDs are rapidly gaining popularity as sources of illumination, as in LCD backlights, but with forward voltages typically ranging from 3 to 5V, operating them from a single cell presents obvious difficulties. This circuit is based on SN74AUC1G14 IC’s. This is the figure of the circuit.


The operation of the circuit begin, when you first apply battery power, Schottky diode D1 conducts, and the familiar Schmitt-trigger astable multi vibrator starts to oscillate at a frequency determined by timing components C2 and R1. When IC1’s output goes high, transistor Q1 turns on, and current begins to ramp up in inductor L1. At the end of tON, when the inverter output goes low, Q1 turns off, and the voltage across L1 reverses polarity. The resulting “flyback” voltage immediately raises Q1’s collector voltage above VBATT and forward-biases the LED and D2, which appear in series.

Digital Distance Counter Measurement

When we take a journey, we must to attention the distance that missing. We need a measurement to measure the distance. In the bicycle, we know that the instrument to measure the distance is make by analog measurement. The design circuit is used to measurement distance with digital measurement. The hardware is located in a small box slipped in pants' pocket and the display is conceived in the following manner: the leftmost display D2 (the most significant digit) shows 0 to 9 Km and its dot is always on to separate Km from hm. This is the figure of the circuit.


The rightmost display D1 (the least significant digit) shows hundreds meters and its dot illuminates after every 50 meters of walking. A beeper (excludable), signals each count unit, occurring every two steps. A normal step was calculated to span around 78 centimeters, thus the LED signaling 50 meters illuminates after 64 steps (or 32 operations of the mercury switch), the display indicates 100 meters after 128 steps and so on. For low battery consumption the display illuminates only on request, pushing on P2. In any case, the most critical thing to do is the correct placement of the mercury switch inside of the box and the setting of its sloping degree.

Operation of the circuit is begin from IC1A & IC1B form a mono stable multi vibrator providing some degree of freedom from excessive bouncing of the mercury switch. Therefore a clean square pulse enters IC2 that divides by 64. Q2 drives the LED dot-segment of D1 every 32 pulses counted by IC2. Either IC3 & IC4 divide by 10 and drive the displays. P1 resets the counters and P2 enables the displays. IC1C generates an audio frequency square wave that is enabled for a short time at each mono stable count. Q1 drives the piezo sounder and SW2 allows to disable the beep.

The Transistor Tester Circuit

This is a very simple design circuit that can be used to check the hfe of transistors. Both PNP and NPN transistors can be checked using this circuit. Hfe as high as 1000 can be measured by using this circuit. The circuit is based on two constant current sources build around transistors Q1 and Q2. This is the figure of the circuit.


Operation of the circuit is the Q1 is a PNP transistor and the constant current flows in the emitter lead. The value of constant current can be given by the equation; (V D1 -0.6)/ (R2+R4).The POT R4 can be adjusted to get a constant current of 10uA.

The Q2 is an NPN transistor and the constant current flows into the collector lead. The value of this constant current can be given by the equation; (VD2-0.6)/(R3+R5).The POT R5 can be adjusted to get a constant current of 10uA.This constant current provided by the Q1 circuit if the transistor under test is an NPN transistor and by Q2 circuit if the transistor under test is a PNP transistor is fed to the base of transistor under test. This current multiplied by the hfe flows in the collector of the transistor and it will be indicated by the meter. The meter can be directly calibrated to read the hfe of the transistor. The Zener diodes must be rated at least 400mW. J1 and J2 are transistor sockets.

VU and PPM Meter Circuit for Audio

A VU (Volume Unit) meters used to be the mainstay of audio metering system. The Peak Program Meter (PPM) is notoriously bad at showing the peak signal level. This is a circuit that have function same of the explanation in above. In this circuit, the amplifier/rectifier is a simple LM1458 or similar dual op-amp, and buffers the rectifier circuit. This is the figure of VU meter;


The principle of the VU meter is a single diode is used in some, but the better ones will generally use a tiny selenium bridge rectifier or a germanium diode bridge. A capacitor is show, few budget VU meters will include it. As a result, the meter movement itself is uncontrolled in most of these meters, so overshoot is often huge, and the reading is almost useless. Because of the diode forward voltage, many of these meters also fail completely to register low level signals (< -20 dB). In figure 2, is shown of the meter's ballistic control for the VU meter. The principle of this circuit is the values of R6, C1, C2 and C3 may need to be adjusted, depending upon the ballistics of the meter movement you use. Because meters vary so widely in this respect, it is only possible to provide representative values, although they should work quite well in practice. In order to get exact VU meter ballistics, it will be necessary to test the meter with a 300ms burst waveform at full scale (+3VU). It should reach 99% of full scale with up to 1% of overshoot before dropping back to zero. If we want to know about the result of the VU meter testing, we must make the circuit.

LED Audio VU Meter Circuit

The LED meter circuit is simpler and smaller than its analogue counterpart, and is very common in audio equipment. This circuit is based on LM3915 IC and uses the logarithmic version. This circuit is using a single IC and a few discrete components. The extra diode (D3) is included to ensure that the DC to the LEDs is almost unfiltered. C1 is included to make sure the IC does not oscillate, and is not a filter capacitor. This allows a higher LED current with lower dissipation than would be the case if the DC were fully smoothed, and full smoothing would also require a much larger capacitor. This is the figure of the LED audio VU meter circuit;


How is this circuit work? We will explain with simple ways. L1 to L8 will normally be green (normal operating range) and L9 and L10 should be red (indicating overload). This gives a 6dB overload margin when the unit is calibrated as described below. As shown, full scale sensitivity (with VR1 at maximum) is 12 Volts peak (approximately 8.5 volts RMS). This is designed for direct connection to the speaker output of an amplifier, but is still suitable for use with preamps if the sensitivity is changed. Power comes from a 15-0-15 transformer (connected to AC1-Com-AC2). You can generally use the smallest one available, as average power is quite low. The peak current is about 120mA DC, so a 5VA transformer will be sufficient to power two meter circuits. One 15V winding goes to the terminal AC1, the other goes to AC2 and the centre tap is connected to Com (Common).

Inductance Meter Adapter Circuit

The inductance meter adapter circuit output is connected with a frequency meter and the inductance is calculated from the frequency. So, you will need a frequency meter and some calculation to get your inductor value. The circuit enables to measure inductance of the inductor which is the inductance to be measured. The operation of the circuit is built by a TTL square wave whose frequency relates to the inductance being measured. This the figure of the circuit;


How is the circuit work? The core of the circuit is the buffer colpitts oscillator(the first stage) which resonates with the unknown inductance to give a sinus wave of a particular frequency . The frequency of the sinus wave is a function of the unknown inductance and the four 1000pF C. The output sinus wave is amplified by the second transistor and is then rectified by the capacitor and diode combination that follows. The rectified sine wave now having only positive excursions is buffered by the third transistor and is then fed to the 74ls393. Counter IC which is configured as a divide by 256 counters. The output of the IC pin 6 and ground is connected to the frequency meter.