Supply Voltage Monitor Circuit

Here’s a design circuit for monitoring supply voltages of ±5 V and ±12 V is readily constructed as shown in the diagram. It is appreciably simpler than the usual monitors that use comparators, and AND gates. Here’s the figure of the circuit;

The circuit is not intended to indicate the level of the inputs. In normal operation, transistors T1 and T3 must be seen as current sources. The drop across resistors R1 and R2 is 6.3 V (12 –5 –0.7). This means that the current is 6.3mA and this flows through diode D1 when all four voltages are present. However, if for instance, the –5 V line fails, transistor T3 remains on but the base-emitter junction of T2 is no longer biased, so that this transistor is cut off. When this happens, there is no current through D which then goes out.

Non-Contact Power Monitor Circuit

This is a design circuit for non-contact AC power monitor for home appliances and laboratory equipment that should remain continuously switched-on. This circuit is built around CMOS IC CD4011 utilizing only a few components. NAND gates N1 and N2 of the IC are wired as an oscillator that drives a piezo buzzer directly. This is the figure of the circuit;

Resistors R2 and R3 and capacitor C2 are the oscillator components. The amplifier comprising transistors T1 and T2 disables the oscillator when mains power is available. In the standby mode, the base of T1 picks up 50Hz mains hum during the positive half cycles of AC and T1 conducts. This provides base current to T2 and it also conducts, pulling the collector to ground potential. As the collectors of T1 and T2 are connected to pin 2 of NAND gate N1 of the oscillator, the oscillator gets disabled when the transistors conduct. Capacitor C1 prevents rise of the collector voltage of T2 again during the negative half cycles. When the power fails, the electrical field around the equipment’s wiring ceases and T1 and T2 turn off. Capacitor C1 starts charging via R1 and preset VR and when it gets sufficiently charged, the oscillator is enabled and the piezo buzzer produces a shrill tone. Resistor R1 protects T2 from short circuit if VR is adjusted to zero resistance. The circuit can be easily assembled on a perforated/breadboard. Use a small plastic case to enclose the circuit and a telescopic antenna as aerial. A 9V battery can be used to power the circuit. Since the circuit draws only a few microamperes current in the standby mode, the battery will last several months.

Telephone Line Monitor Circuit

This is a circuit that will find application in the case where you have a lot of telephones installed on a telephone line and would want to know if somebody of them is open. Thus you will not be off any discussion. Simultaneously it can cut the certain sound from stereo amplifier that are in high volume, the sound of some television or turn on some light the night when it ring the telephone and needs him you raise. Here’s the figure of the circuit;

Exists a pair of free contacts of RL1 that connects to the J2, which you can use connecting there any appliance you want. The telephone line connected in the J1, with what polarity you wants. When the telephone is closed then the line voltage is roughly, 48-50Vdc. This voltage turn on the photo diode and this, the transistor of IC1, which it simultaneously isolates, the circuit from the telephone line. The photo transistor in IC1 are now in situation ON, the input of IC2A are LOW [L] and output HIGH [H]. Ignoring for little the circuit of delay D6, R4, R5, C1, the IC2B input, are also this HIGH hence the output are LOW, transistor Q1 are OFF and the RL1 are deactivate. When the telephone earphone is raised, then the telephone voltage line fall in 6-10Vdc.

All the previous situation is reversed also the RL1, turn on. The telephones that use for dial choice, disk or pulse system, can they open and close the RL1 at the duration of choice. With delay network, that exist between in gates IC2A and in the IC2B, we delay the situation changes in the input of IC2B, ensuring thus stability in the operation of RL1. If the R4=100K then the RL1 is activated when the telephone ring or when the earphone is raised. On the contrary if the R4=1M, then the RL1 is activated only when the earphone is raised. The circuit supply becomes with a simple regulation circuit, in + 12V.

Part:

R1-2=36Kohm
R3=100Kohm
R4=100Kohm or 1Mohm 
R5=2.2Mohm
R6=3.3Kohm
R7=1Kohm
D1....4=1N4002
D5=1N5252 [24V 0.5W Zener]
D6-7=1N4148
D8....11=1N4002
D12=Red Led 3 or 5mm
RL1=12Vdc 2X2 relay
J1-4=2pin connector 2.54mm step
J2=6pin connector 5mm step
J3=2pin connector 5mm step
F1=Fuse 500mA [5x20mm]
C1=100 or 220nF 100V MKT
C2=1000uF 25V
C3-4=100nF 100V
C5=4.7uF 16V
IC1=4N25 opto coupler
IC2=4011B
IC3=7812 [1A]
Q1=BD139 or BD679
T1=12Vac 500ma tranformer for pcb

9V Battery Voltage Monitor Circuit

This is a circuit that can be use for monitoring the voltage of battery. This is the figure of the circuit;

Nine voltage batteries are used in a wide variety of electronic devices.  But, you often don’t know when it is time to change the battery until the device stops operating.  The hobby circuit below provides a visual indication when the battery needs to be replaced.  It uses a neat IC from Linear Technology, which contains a very low power voltage reference and a voltage comparator.  The circuit is designed to turn on a LED indicator light when the battery voltage drops below 7.2 volts. [Circuit schematic source: discovercircuits.com]

Board System Monitoring Circuit for Temperature and Voltage Condition

This is a design circuit of board system monitoring for temperature and voltage condition. This circuit uses the NE1617A. The NE1617A is a 2 channel temperature sensor. It can measure remote and internal sensor. It also supports up to nine devices per bus. The temperature data update is selectable from 125 ms to 16 seconds, if it is used in normal operation. An internal, the temperature reading can be forced by one-shot command. This is the figure of the circuit.

The advantage of the NE1617A is programmable, has high accuracy, small, 16-pin QSOP packages and has an operating temperature of 0 to 120 °C. It can be used for applications where thermal monitoring of electrical components and hardware is critical. The more advanced version of the NE1617A is the NE1619. Besides measures the remote and internal temperature, the NE1619 can be used to monitor nine different voltages. It has programmable voltage  and temperature limits for controlling internal alarms and  supports two devices per bus. It also has an on-chip A/D converter which supports data collection and other functions. The consistent conversion rate that is used by the NE1619 is approximately 500 ms. [Circuit schematic source:  NXP Application Note]

Carrier Based Current Monitor

This circuit is utilizes AC carrier modulation techniques to meet APD current monitor requirements. This circuit features 0.4% accuracy over the sensed current range, runs from a 5V supply and has the high noise rejection characteristics of carrier based “lock in” measurements. This is the figure of the circuit.

This circuit is based on The LTC1043 that is used to switch array is clocked by its internal oscillator. Oscillator frequency, set by the capacitor at Pin 16, is about 150Hz. S1 clocking biases Q1 via level shifter Q2. Q1 chops the DC voltage across the 1kW current shunt, modulating it into a differential square wave signal which feeds A1 through 0.2mF AC coupling capacitors. A1’s single-ended output biases demodulator S2, which presents a DC output to buffer amplifier A2. A2’s output is the circuit output. Switch S3 clocks a negative output charge pump which supplies the amplifier’s V– pins, permitting output swing to (and below) zero volts. The 100k resistors at Q1 minimize its on-resistance error contribution and prevent destructive potentials from reaching A1 (and the 5V rail) if either 0.2mF capacitor fails. A2’s gain of 1.1 corrects for the slight attenuation introduced by A1’s input resistors. In practice, it may be desirable to derive the APD bias voltage regulator’s feedback signal from the indicated point, eliminating the 1kW shunt resistor’s voltage drop. [Schematic’s circuit source: Linear Technology Notes].

Trans-Impedance Amplifier for DAC Outputs Using LH4117 Single IC Chip

This is a circuit for trans-impedance amplifier that using to DAC output. This circuit is based on LF4117 that is an excellent match to amplify the output of DACs like the DAC0800. The fast settling time of 9 ns to 0.02% does not degrade the performance of the DAC. On the other hand, the DAC0800 provides complimentary current outputs, which are current sinks and do not need a fixed voltage to work accurately. This is the figure of the circuit.

The DAC0800 is fed a reference current of IREF e 2 mA into pin 14. This is achieved by the LH0070 voltage reference with 10V output. A resistance of 5 kX (R1 a R2) is connected to pin 14, which is a virtual ground, thus providing the reference current of 2 mA. The grounded pin 15 provides the reference voltage for pin 14. The DAC has eight current sinks, each set for half the current of the previous one. Through switches, controlled by the input logic levels, their open collectors are connected to one of the two outputs. The sum of the output currents I1 and I2 equals the reference current of 2 mA. Because of the open collector configuration the outputs do not have to be tied to a fixed voltage level. The outputs of the DAC0800 are connected to the inputs of the LH4117 through 100X resistors (R4 and R5). This is to decouple the inputs of the amplifier from the output capacitance of the DAC, which is typically 23 pF to 30 pF. Especially the inverting input is sensitive to capacitance. [Schematic’s circuit source: National Semiconductor Notes].

DC Coupled Current Monitor Circuit

This is design circuit for DC coupled current monitor that is eliminates the previous circuit’s trim but pulls more current from the APD bias supply. A1 floats powered by the APD bias rail. This is the figure of the circuit.

The 15V zener diode and current source Q2 ensure A1 never is exposed to destructive voltages. The 1kW current shunt’s voltage drop sets A1’s positive input potential. A1 balances its inputs by feedback controlling its negative input via Q1. As such, Q1’s source voltage equals A1’s positive input voltage and its drain current sets the voltage across its source resistor. Q1’s drain current produces a voltage drop across the ground referred 1k resistor identical to the drop across the 1kW current shunt and, hence, APD current. This relationship holds across the 20V to 90V APD bias voltage range. The 5.6V zener assures A1’s inputs are always within their common mode operating range and the 10M resistor maintains adequate zener current when APD current is at very low levels.

Two output options are shown. A2, a chopper stabilized amplifier, provides an analog output. Its output is able to swing to (and below) zero because its V– pin is supplied with a negative voltage. This potential is generated by using A2’s internal clock to activate a charge pump which, in turn, biases A2’s V– pin. A second output option substitutes an A-to-D converter, providing a serial format digital output. No V– supply is required, as the LTC2400 A-to-D will convert inputs to (and slightly below) zero volts. [Schematic’s circuit source: Linear Technology Notes].

APD Bias Supply and Current Monitor

This circuit is consists of two circuit but in the figure this circuit is combines. This is the figure of the circuit.

The programmable APD bias supply is as before, except that feedback comes via A2. A2, sensing after the 1kW current shunt, isolates the R1-R2 path loading, preventing it from influencing the shunt’s voltage drop. A2’s action also insures tight output regulation, despite the current shunt’s presence. The current monitor, measures across the 1kW current shunt, presenting its output in Q1’s drain line. As shown, the output has about 1kW output impedance, although either of the circuit output options may be employed.

When considering circuit operation, note that both amplifiers are powered by the charge pump’s high voltage output, with their V– pin returned to the “2/3 VOUT” point. This biasing permits the amplifiers to process high voltage signals, although the voltage across them never exceeds 30V.