LM134-LM10 Thermometer/Temperature Sensor Circuit

This circuit is use to build a thermometer which has -55 to 150°C sensing range.  The ideal meter for this circuit is a 0-200uA digital ampere meter, which can show both positive and negative polarity. This will make the circuit suitable for indicating temperatures below 0°C. Here’s the figure of the circuit;

This circuit is based on LM134 and LM10 that has basically a current source with very accurate and consistent temperature coefficient, so many temperature sensing application find it suitable for the sensor. [Circuit diagram source: National Semiconductor Notes]

High Impedance Voltmeter Circuit

This is the design circuit off ideal voltmeter has infinite input impedance, meaning that it draws zero current from the circuit under test. This way, there will be no "impact" on the circuit as the voltage is being measured. The more current a voltmeter draws from the circuit under test, the more the measured voltage will "sag" under the loading effect of the meter, like a tire-pressure gauge releasing air out of the tire being measured: the more air released from the tire, the more the tire's pressure will be impacted in the act of measurement. This loading is more pronounced on circuits of high resistance, like the voltage divider made of 1 MΩ resistors. This is the figure of the circuit;

 

If you were to build a simple 0-15 volt range voltmeter by connecting the 1 mA meter movement in series with the 15 kΩ precision resistor, and try to use this voltmeter to measure the voltages at TP1, TP2, or TP3 (with respect to ground), you'd encounter severe measurement errors induced by meter "impact:" If we were to increase the meter's input impedance, we would diminish its current draw or "load" on the circuit under test and consequently improve its measurement accuracy. An op-amp with high-impedance inputs (using a JFET transistor input stage rather than a BJT input stage) works well for this application.

Note that the meter movement is part of the op-amp's feedback loop from output to inverting input. This circuit drives the meter movement with a current proportional to the voltage impressed at the non-inverting (+) input, the requisite current supplied directly from the batteries through the op-amp's power supply pins, not from the circuit under test through the test probe. The meter's range is set by the resistor connecting the inverting (-) input to ground.

Build the op-amp meter circuit as shown and re-take voltage measurements at TP1, TP2, and TP3. You should enjoy far better success this time, with the meter movement accurately measuring these voltages (approximately 3, 6, and 9 volts, respectively).

Radio Frequency (RF) Watt Meter Circuit

This is a circuit for RF (radio frequency) transmitter experiment, watt meter is useful for optimizing the transmitter circuit. A simple RF watt meter circuit is shown in the schematic diagram below. Because circuit is not frequency sensitive, calibration is accurate on all HF bands. The sensitivity is affected by meter movement, number of turns in primary coil, and resistive voltage driver. This is the figure of the system;

Pots can be adjusted for full-scale values from 1-14 W with values shown on the diagram. C1 and C2 are 3-20 pF. Diodes are 1N34A, 1N60, or equivalent. L1 is 46 turns No. 28 on Amidon T-50-2 toroid, with 2 turns No. 22 between ends of L1 for L2. Connect resistive dummy load to one coax receptacle and RF power source to other to adjust, with R2 at maximum resistance. We can provide highest meter reading and make that the FWD position with place the switch on the upper position. Switch to other position, which becomes REF, and for null reading, adjust C1. Reverse RF source and load, leaving switch at FWD, and adjust C2 for null. Now, we can calibrated the Wattmeter.

Linear Resistance Meter Circuit

This is a one design circuit for analogue multi meters are capable of measuring resistance over quite a wide range of values, but are rather inconvenient in use due to the reverse reading scale which is also non-linear. This can also give poor accuracy due to cramping of the scale that occurs at the high value end of each range. This is the figure of the circuit;

This resistance meter has 5 ranges and it has a forward reading linear scale on each range. The full-scale values of the 5 ranges are 1K, 10K, 100K, 1M &10M respectively and the unit is therefore capable of reasonably accurate measurements from a few tens of ohms to ten Mega ohms. Most linear scale resistance meters including the present design, work on the principle that if a resistance is fed from a constant current source the voltage developed across that resistance is proportional to its value. For example, if a 1K resistor is fed from a 1 mA current source from Ohm’s Law it can be calculated that 1 volt will be developed across the resistor (1000 Ohms divided by 0.001 amps = 1 volt). Using the same current and resistance values of 100 ohms and 10K gives voltages of 0.1volts (100 ohms / 0.001amps = 0.1volts) and 10 volts (10000 ohms / 0.001amps = 10 volts). Thus the voltage developed across the resistor is indeed proportional to its value, and a voltmeter used to measure this voltage can in fact be calibrated in resistance, and will have the desired forward reading linear scale. One slight complication is that the voltmeter must not take a significant current or this will alter the current fed to the test resistor and impair linearity. It is therefore necessary to use a high impedance voltmeter circuit.

Electromagnetic Field Probe Circuit Using Meter Output

This circuit is designed to locate stray electromagnetic (EM) fields. It will easily detect both audio and RF signals up to frequencies of around 100kHz. Note, however that this circuit is NOT a metal detector, but will detect metal wiring if it conducting ac current. This is the figure of the circuit;

Frequency response is from 50Hz to about 100kHz gain being rolled off by the 150p capacitor, the gain of the op-amp and input capacitance of the probe cable. Stereo headphones may be used to monitor audio frequencies at the socket, SK1. The output signal from the op-amp is an ac voltage at the frequency of the electro-magnetic field. This voltage is further amplified by the BC109C transistor, before being full wave rectified and fed to the meter circuit. The meter is a small dc panel meter with a FSD of 250uA. Rectification takes place via the diodes, meter and capacitor. Switch on, plug in headphones (optional) and move the probe around. Any electrical equipment should produce a hum and indicate on the meter. It remember once building a high gain preamp (for audio use). I made a power supply in the same enclosure. The preamp worked, but suffered from an awful mains hum. This was not directly from ripple on the power supply as it was regulated and well smoothed. What I had done was built the audio circuit on a small piece of veroboard, and placed it within a distance that was less than the diameter of the transformer.

LED VU Meter Circuit Using LM3915 IC

This LED VU Meter (volume-unit) is capable of monitoring and displaying power levels present at the speaker terminals of an stereo audio power amplifier. The levels are displayed in ten discrete steps using 10 LEDs for each channel. This project is designed to give an approximate visual indication of the audio power output of each channel. This is the figure of the circuit;

Two external resistors (R2 & R3) programs the full scale from between 1.2V and 12V applied to pin 5. 10.5V is used to turn on all 10 LED's. The voltage required to turn on all the LEDs is set by R2 and R3. The IC develops a nominal 1.25V reference voltage (Vref) across pins 7 and 8. Since this voltage is constant then the current through R3 is also constant. This current also flows through R2. The total voltage across R2 and R3 is given by voltage. Internally this chip consists of ten voltage comparators. The non-inverting (+) input of each comparator is connected to an accurate ten-step voltage divider network. Each comparator will therefore trigger on a different comparison level. The inverting (-) inputs of each comparator are commoned together and connected to an incoming DC signal via a high impedance input buffer.

Decibel Sound Pressure Level Meter Circuit

This is a design for decibel meter circuit. This circuit is used to measure sound pressure level (SPL) from about 60 to 70 dB. In this circuit, the transistor stage and one LM324 op-amp section are used to amplify the sound that is picked up by an 8 ohm speaker. As voltage comparators, the circuit uses The remaining 3 sections of the LM324 quad op-amp. 3 indicator LEDs are driven by the LM324. This is the figure of the circuit;


This circuit uses 3 LEDs as indicators. Each LED represents about a 3dB change in sound level, so that when all 3 LEDs are on, the sound level is about 4 times greater than the level needed to light one LED. the 500K pot can be used to adjust the sensitivity of the circuit. One LED is used as a reference sound level. The other two LEDs is used to indicate about a 2X and 4X increase in volume.

Digital Step Km Counter Circuit

This circuit is designed for measures the distance covered during a walk. 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. The rightmost display D1 (the least significant digit) shows hundred meters and its dot illuminates after every 50 meters of walking. A beeper (excludable), signals each count unit, occurring every two steps. This is the figure of the circuit;

This circuit has operation with based on 2 IC. 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 disabled the beep.

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. Accidental reset of the counters is avoided because to reset the circuit both pushbuttons must be operated together.

Part:

R1,R3____22K 1/4W Resistor

R2________2M2 1/4W Resistor

R4________1M 1/4W Resistor

R5,R7,R8__4K7 1/4W Resistor

R6_______47R 1/4W Resistor

R9________1K 1/4W Resistor

C1_______47nF 63V Polyester Capacitor

C2______100nF 63V Polyester Capacitor

C3_______10nF 63V Polyester Capacitor

C4_______10µF 25V Electrolytic Capacitor

D1_______Common-cathode 7-segment LED mini-display (Hundreds meters)

D2_______Common-cathode 7-segment LED mini-display (Kilometers)

IC1______4093 Quad 2 input Schmitt NAND Gate IC

IC2______4024 7 stage ripple counter IC

IC3,IC4__4026 Decade counter with decoded 7-segment display outputs IC

Q1,Q2___BC327 45V 800mA PNP Transistors

P1_______SPST Pushbutton (Reset)

P2_______SPST Pushbutton (Display)

SW1______SPST Mercury Switch, called also Tilt Switch

SW2______SPST Slider Switch (Sound on-off)

SW3______SPST Slider Switch (Power on-off)

BZ_______Piezo sounder

B1_______3V Battery (2 AA 1.5V Cells in series)

Salt Tester Circuit

This circuit was designed to detect the approximate percentage of salt contained in a liquid. After careful setting it can be useful to persons needing a quick, rough indication of the salt content in liquid foods for diet purposes etc. This circuit is using LM324 as main components. This is the figure of the circuit;

IC1A op-amp is wired as a DC differential amplifier and its output voltage increases as the DC resistance measured across the probes decreases. In fact, fresh water has a relatively high DC resistance value that will decrease proportionally as an increasing amount of salt is added. IC1B, IC1C and IC1D are wired as comparators and drive D5, D4 and D3 in turn, as the voltage at their inverting inputs increases. Therefore, no LED will be on when the salt content of the liquid under test is very low, yellow LED D5 will illuminate when the salt content is low, green LED D4 will illuminate if the salt content is normal and red LED D3 will illuminate if the salt content is high. D1 and D2 are always on, as their purpose is to provide two reference voltages, thus improving circuit precision. At D2 anode a stable 3.2V supply feeds the non-inverting inputs of the comparators by means of the reference resistor chain R8, R9 and R10. The 1.6V reference voltage available at D1 anode feeds the probes and the set-up trimmer R4. One of these two red LEDs may be used as a pilot light to show when the device is on.

Parts:

R1________________470R 1/4W Resistor

R2,R5______________10K 1/4W Resistors

R3,R6_____________220K 1/4W Resistors

R4__________________5K 1/2W Trimmer Cermet

R7________________680R 1/4W Resistor

R8__________________2K2 1/4W Resistor

R9,R10,R11,R12,R13__1K 1/4W Resistors

C1________________100µF 25V Electrolytic Capacitor

D1,D2,D3______3 or 5mm. Red LEDs

D4____________3 or 5mm. Green LED

D5____________3 or 5mm. Yellow LED

IC1_______________LM324 Low Power Quad Op-amp

P1_________________SPST Pushbutton

Probes_________________ (See Text)

B1___________________9V PP3 Battery

Clip for PP3 Battery

Non Interacting Adjustments for Expanded Scale Meter

This is one application for function of LM3814. This circuit is called expanded scale meter. This is the figure of the circuit.


This arrangement allows independent adjustment of LED brightness regardless of meter span and zero adjustments. First, V1 is adjusted to 5V, using R2. Then the span (voltage across R4) can be adjusted to exactly 0.5V using R6 without affecting the previous adjustment. R9 programs LED currents within a range of 2.2mA to 20mA after the above settings are made. [Schematic diagram source: National Semiconductor, Inc]

20 Segment Meter Circuit with Mode Switch

This is a schematic circuit for ones application for segment meter circuit using mode switch. This circuit is based on LM3914 that is a monolithic integrated circuit that senses analog voltage levels and drives 10 LEDs, providing a linear analog display. This is the figure of the circuit.


The most difficult problem occurs when large LED currents are being drawn, especially in bar graph mode. These currents flowing out of the ground pin caused voltage drops in external wiring, and thus errors and oscillations. Bringing the return wires from signal sources, reference ground and bottom of the resistor string (as illustrated) to a single point very near pin 2 is the best solution. In cases where proper wiring and bypassing fail to stop oscillations, V+ voltage at pin 3 is usually below suggested limits. Expanded scale meter applications may have one or both ends of the internal voltage divider terminated at relatively high value resistors. These high-impedance ends should be bypassed to pin 2 with at least a 0.001μF capacitors, or up to 0.1μF in noisy environments. Power dissipation, especially in bar mode should be given consideration.[Schematic source: Linear Technology Corporation].

Auto Ranging Circuit Using LTCxxxx IC

This is a circuit that is the name called auto ranging circuit. This circuit is useful to extend the measurement range of an available ADC (analog-to-digital converter). The circuit will best implemented for multiplexed input. LTC1257 is appropriate for system auto ranging, adjusting an ADC’s full-scale range. This is the picture of the schematic.


This circuit is use IC with LTC type. During the conversion process, U2 and U3 receive the full and zero scale codes, respectively, that correspond to a selected multiplexer channel. For example, let channel 2’s span begin at 2V and end at 4.5V. When a host processor wants a conversion of channel 2’s input signal, it first sends code that sets the output of U2 to 2V and U3 to 4.5V, fixing the span to 2.5V. The processor then sends data to the LTC1296 selecting channel 2. The processor next clocks the LTC1296 and reads the data generated during the conversion of the 3.5VP-P signal applied to channel 2. As other multiplexer channels are selected the DAC outputs are changed to match their spans.

Fahrenheit Thermometer Circuit Using LM35

This is a design for thermometer. This is a ones simple circuit. If you have a digital voltmeter, or any voltmeter with milli volt resolution and high input impedance, then you can use this temperature-to-voltage adapter circuit to measure room temperature. This circuit is based on LM35 as temperature sensor. This is the figure of the circuit.


Note that the voltage output of this circuit is floating, not referenced to ground. You have to use separate supply if your voltmeter has single ended (referenced to ground) input. You can set your voltmeter to 200 mV range to give temperature reading directly in Fahrenheit degree. [Schematic source: National Semiconductor Application Notes]

Simple Audio Level Meter Using LM3915

This is a simple design of audio level meter. This circuit uses just one IC and a very few number of external components. This circuit is based on LM3915 as controller in the operation of the audio level meter circuit. It displays the audio level in terms of 10 LEDs. The input voltage can vary from 12V to 20V, but suggested voltage is 12V. This is the figure of the circuit.


The LM3915 is a monolithic integrated circuit that senses analog voltage levels and drives ten LEDs providing a logarithmic 3 dB/step analog display. LED current drive is regulated and programmable, eliminating the need for current limiting resistors. The IC contains an adjustable voltage reference and an accurate ten-step voltage divider. The high-impedance input buffer accepts signals down to ground and up to within 1.5V of the positive supply. Further, it needs no protection against inputs of 35V. The input buffer drives 10 individual comparators referenced to the precision divider. Accuracy is typically better than 1 dB.