Multiple Continuity TesterThe continuity tester is a handy adjunct to an ohmmeter. The unit or component whose continuity is to be checked is connected between terminals E1 and E2 (which may be probes or croc clips). The test current then flowing through the unit/component on test causes a potential drop across resistor R2, which is applied to the non-inverting input of buffer IC2. The output of the op amp is applied to transistor T1, in the emitter circuit of which there are a number of parallel-connected light-emitting diodes. Each LED is in series with a zener diodes and a resistor. The zener diodes have dissimilar zener voltages as shown in the diagram. When the drop across R2 exceeds the sum of base-emitter voltage of T1, a zener voltage, and the threshold voltage of the LED in series with that zener diode, the relevant LED lights.

The diagram shows at which resistance value of the unit/component on test a particular LED lights. Bear in mind, however, that these values depend to some extent on the type of LED, and also that the zener voltages are subject to tolerances. Serious deviations may be corrected by the addition of a standard diode or a Schottky diode. It is also possible to add branches to individual requirements, or to use a bar display instead of LEDs. It is important that the op amp used has a rail-to-rail output since the input voltages as well as the output may rise to the peak supply voltage. This requirement is met by the MAX4322 as used in the prototype.

Continuity Tester Circuit DiagramHaving good contacts is important – not only in your daily life, but also in electronics. In contrast to social contacts, the reliability of electrical contacts can be checked quickly and easily. Various types of continuity testers are commercially available for this purpose. Most multimeters also have a continuity test function for electrical connections. A simple beep helps you tell good contacts from bad ones.

However, in some cases the tester doesn’t produce a beep because it won’t accept contact resistances that are somewhat higher than usual. Also, poorly conducting (and thus bad) connections are sometimes indicated to be good. Here e-trix comes to your aid with a design for a DIY continuity tester that helps you separate the wheat from the chaff.

Circuit diagram:

Continuity Tester Circuit SchematicCircuit description:

Many multimeters have a built-in continuity test function. However, in many cases the resistance necessary to activate the beeper when you are looking for bad connections is just a bit too high. It can also happen that the beeper sounds even though the resistance of the connection is unacceptably high. This circuit lets you adjust the threshold between bad and good contacts to suit your needs. The circuit is built around an operational amplifier (IC1) wired as a comparator.

The opamp compares the voltage on its inverting input (pin 2) with the voltage on its non-

inverting input (pin 3). The voltage on pin 3 can be set using potentiometer P1, so you can set the threshold between good and bad connections. When test probes TP1 and TP2 are placed on either side of a connection or contact to be tested, a voltage is generated across the probes by the current growing though resistors R1 and R3, and it appears on pin 2 of the opamp. This voltage depends on the resistance between the probe tips.

If the voltage on pin 2 is lower than the reference voltage on pin 3, the difference is amplified so strongly by the opamp that its output (pin 6) is practically the same as the supply voltage. This causes transistor T1 to conduct, which in turn causes DC buzzer BZ1 to sound. This means that the resistance of the connection being tested is less than the threshold value set by P1, and thus that the connection is OK.

By contrast, a bad connection will cause the relationship between the voltages on the inputs of the opamp to be the opposite, with the result that its output will be at ground level. The transistor will not conduct, and the buzzer will remain still. To ensure that the opamp ‘toggles’ properly (which means that its output goes to ground level or the supply voltage level) when the difference voltage is sufficiently large and does not oscillate during the transition interval due to small fluctuations in the difference voltage produced by interference, its output is coupled back to its non-inverting input (pin 3) by resistor R4.

This causes any change on the output to be passed back to this input in amplified form, with the result that the detected difference voltage is amplified (and thus boosted). Diodes D1, D2 and D3 protect the circuit against excessive positive and negative input voltages that may come from the connections or contacts being tested. They also ensure that the continuity tester does not inject excessively high voltages into the item under test. Capacitor C1 suppresses high-frequency interference. The circuit draws only a small supply current, so it can easily be powered by a 9-V battery.

Three-State Continuity TesterThe continuity tester can distinguish between high-, medium-, and low-resistance connections. When there is a conductance between the inputs, which are linked to small probes, a current flows from the +9 V line to earth via R1 and R2. The consequent potential difference, p.d., across R2 is used to determine the transfer resistance. Operational amplifier IC1c amplifies the p.d. across R2 to a degree that is set with P1. A window comparator, IC1a and IC1b, likens the output of IC1c to the two levels set with potential divider R4–R6. Depending on the state of the outputs of the two comparators, three light-emitting diodes (LEDs) are driven via the gates and inverters contained in IC3 and IC2 respectively in such a way that they indicate the transfer

resistance in three categories.

Circuit diagram:Three-State Continuity Tester Circuit Diagram

When the resistance is high, green diode D3 lights; when it is of medium value, yellow diode D2 lights, and when it is low, red diode D1 lights. The levels at which the diodes light is set with P1, but note that in any case the minimum value depends on the p.d. across R2. It is possible to reduce the value of the p.d. to enable lower transfer resistances to be detected, but this would mean an increase in the test current through R2. With values as specified, the circuit in its quiescent state draws a current of about 17 mA, but in operation each LED adds about 10 mA to this. The LM324 (IC1) may be operated from a single supply line: R1 prevents the voltage at the input from reaching the level of the supply line (which is not permissible). The supply voltage may be 5–18 V. The LEDs are driven directly by the inverters in the 4049 (IC2), which can switch currents of up to 20 mA to earth.

Circuit Continuity Tester Using Op-Amps

The circuit was developed to produce a continuity tester with a low resistance mainly for checking the connections between soldered joints.

Operational Amplifier (Op-Amp) – a DC coupled high gain electronic voltage amplifier with differential inputs and usually a single output

Light Emitting Diode (LED) – a semiconductor diode that is commonly a source of light when electric current pass through it

741 Op-Amp – the most common and cheapest op-amp used in several circuits because of 1 MHz gain bandwidth product and is not prone to producing false oscillations due to tailored frequency response

The use of a 741 op-amp to fully function the circuit provides several features such as high input voltage range, excellent temperature stability, no latch up, short circuit protection, offset voltage null capability, and internal frequency compensation. As it operates in differential mode, it provides high input impedance and low noise amplification in the input stage. Specifically, the input being amplified comes from the voltage difference between the inverting and non-inverting inputs. The amplification is done by the full open loop gain of the op-amp which is developed when there is no feedback used in the circuit. However, in the presence of increasing frequency, the open loop gain of an operational amplifier falls very quickly.

The addition of 470K ohm and 10K ohm resistors in the circuit is very essential since they are responsible for creating a minimal voltage difference to be applied to the inputs of the op-amp. Without these resistors, if both resistors connected to the op-amp inputs are ideally equal, the circuit would be balanced wherein the output from the probes would be zero thus producing zero voltage difference. On the other hand, as this voltage difference is amplified, there will be a swing to full supply by the op-amp output which will cause the LEDs to shed light.

Before using the circuit for live testing, the probes should be connected initially to a resistor having a value between 0.22 ohm and 4 ohms. This is done to adjust the control until the LEDs give light while having this resistor across the probes. After the adjustment, the resistor must be removed while shorting the probes so that the LED light will disappear. The probes should be

kept clean and free from dirt to avoid the increase in resistance and the circuit not to function well because the circuit itself has an extremely low resistance value.

I cases where the LEDs do not switch off, the 10K ohm preset resistor should be connected across the offset null terminals which is the Pin 1 and Pin 5 on the metal can package. These offset null terminals are responsible for eliminating the effects of internal component voltages on the output of the device. The wiper of the potentiometer or the control should be connected to the negative terminal of the battery terminal. This offset circuit will work at 0V and –Vcc and will behave as a comparator where it compares two voltages or currents and switches its output for indication of which is higher.

The 741 may be used in two ways. First, it can be used as an inverting amplifier where the negative input is coming from the Pin 2 and the output on Pin 6 with the polarity being reversed. Secondly, it can be used as a non-inverting amplifier where the positive input comes from Pin 3 and the out still at Pin 6 with the polarity being retained.

The continuity tester utilizes a test wire with normally alligator clip connected to the end. It is used mainly to find the cause of problem in a circuit or if a particular electronic component is containing electricity, but with the absence of the current. It is also useful in determining if an electrical path is possible on both ends, which is also similar to testing a bundle of wires to locate the two ends that belong to the same wire.

Before using the continuity tester, make sure that the power is unplugged or the power to the circuit is turned OFF to avoid unwanted injuries.

Connection TesterA low resistance ( 0.25 - 4 ohm) continuity tester for checking soldered joints and connections.

This simple circuit uses a 741 op-amp in differential mode as a continuity tester. The voltage difference between the non-inverting and inverting inputs is amplified by the full open loop gain of the op-amp. Ignore the 470k and the 10k control for the moment, and look at the input of the op-amp. If the resistors were perfectly matched, then the voltage difference would be zero and output zero. However the use of the 470k and 10k control allows a small potential difference to be applied across the op-amp inputs and upset the balance of the circuit. This is amplified causing the op-amp output to swing to full supply voltage and light the LED's.

Circuit diagram:Connection Tester Circuit Diagram

Setting Up and Testing:

The probes should first be connected to a resistor of value between 0.22 ohm and 4ohm. The control is adjusted until the LED's just light with the resistance across the probes. The resistor should then be removed and probes short circuited, the LED's should go out. As the low resistance value is extremely low, it is important that the probes, (whether crocodile clips or needles etc) be kept clean, otherwise dirt can increase contact resistance and cause the circuit to mis-operate. The circuit should also work with a MOSFET type op-amp such as CA3130, CA3140, and JFET types, e.g. LF351. If the lED's will not extinguish then a 10k preset should be wired across the offset null terminals, pins 1 and 5, the wiper of the control being connected to the negative battery terminal.

Simple Cat.5 Network TesterThis circuit came from a need for a "quick and dirty" network tester that could be operated by one person. All the commercial units I tried required a person at the other end to check the remote LEDs, as the transmitters could not be made to cycle through the test continuously to allow one person to check both ends. It must be noted that this unit will only check for pair continuity, pair shorts, crossed wires, and shorts to other pairs. It will not test bandwidth, etc. Operation is fairly basic.

Circuit diagram:

Half of the 4011 quad 2-input NAND gate is an RS flip-flop (IC1a, IC1b) which controls the other half, IC1c & IC1d, operating as a clock oscillator. You can either start and stop the oscillator running by pressing the Start and Stop switches or by virtue of diode D1 connected to pins 12 & 13, use the Stop switch to allow manual clocking of the 4017 counter. The 4017 drives one of eight LEDs and the lines to the RJ45 socket. An output "High" on the 4017 decides which line is under test, and if the circuit is complete, the test LED's current is "sunk" by the 4017 and the LED will light.

If the corresponding test LED on the remote fails to light, then there is a short of that pair in the cable under test. If more than one LED lights, it indicates a short with another pair. A dark test LED on the transmitter indicates that pair is open circuit. "Start" starts the circuit cycling at a rate determined by the 470nF capacitor and 220kO resistor and "Stop/Step" stops cycling, steps through the lines, and when stepped so that no channel LEDs are alight, effectively switches the unit off with a standby drain current of less than a microamp.

Quick On-Board Junction Tester Circuit DiagramAcoustic check of transistor and diode junctions, Also suitable as continuity tester

Short circuits or broken pcb tracks can be easily recognized by means of a Multimeter, but this

tool can give wrong results when testing the efficiency of a transistor or diode, unless the device under test is unsoldered and removed from the pcb. A further shortcoming affecting such way of testing is the necessity to keep firmly the probes on the pins of the device under test and at the same time to turn the head continually to read the Multimeter display.

This device allows the user to concentrate on the (often problematic) pcb probes placement, because a short, a broken track, a good or burnt transistor or diode, will be signaled by a beep, as follows:

A train of short beeps (one per second) indicates an efficient diode or transistor junction A train of one-second lasting beeps spaced by a very short silence (in practice an almost

continuous beep) indicates a shorted junction or, on the contrary, a good pcb track A lack of beeps indicates a broken junction or a broken pcb track

Circuit diagram:

Parts:

R1,R9,R11,R12__100K 1/4W ResistorsR2,R3,R6________10K 1/4W ResistorsR4,R5,R10_______47K 1/4W ResistorsR7_______________1M 1/4W ResistorR8_______________1M5 1/4W ResistorC1_____________100nF 63V Polyester CapacitorC2_______________1µF 63V Polyester or Multilayer Ceramic CapacitorC3,C4___________10µF 25V Electrolytic CapacitorsD1____________1N4148 75V 150mA DiodeQ1_____________BF245 or 2N3819 General-purpose N-Channel FETIC1____________LM358 Low Power Dual Op-ampBZ1____________Piezoelectric sounder (incorporating 3KHz oscillator)SW1____________SPST Toggle or Slide SwitchRed Probe______Insulated probe, Multimeter-likeBlack Probe____The same as aboveB1______9V PP3 Battery Clip for PP3 Battery

Circuit operation:

Both inputs of IC1A are connected together by two equal value resistors (R4 and R5) and to half the voltage supply obtained by means of the voltage divider R2 and R3. So, the same voltage should be present at both input pins.

In practice, half the voltage supply (i.e. about 4.5V) will be present at the inverting input (pin #2) of IC1A, but the constant voltage generator formed by R6 and D1, feeding the non-inverting input (pin #3) of IC1A by means of the voltage divider R7 and R8, clamps this pin to about 4.1 - 4.3V: this will cause the output of the op-amp to stay low.

If the circuit input (R2 to R3 junction) is shorted to negative ground (a condition equivalent to a shorted transistor junction) pin #2 of the op-amp will go to 0V and the voltage at pin #3 will decrease to about 0.3 - 0.35V (caused by the constant voltage generator mentioned above): the op-amp output will go high, activating the piezoelectric sounder.

When a real transistor or diode junction is connected to the input of the circuit instead of shorting the input probes directly, the piezo sounder will emit only a short single beep just as the probes will come in contact with a good junction, due to the time delay provided by the discharge of C2 when the voltage at pin #3 is falling from about 4.1V to 0.3V.

To provide a better signaling system, Fet Q1, IC1B and related components were added. This op-amp is wired as a 1Hz square wave generator and Q1 acts as a solid-state switch, going on and off one time per second having the Gate driven by the op-amp output. In this way, the junction of the device under test is connected and disconnected to the voltage sensitive circuit built around IC1A one time per second and the result will be a clearly audible train of short beeps signaling the good condition of the junction or track under test.

Testing directions:NPN Silicon Transistors:

Place the Red probe on the Base and the Black probe on the Emitter: a train of short beeps should be heard. If not, the junction is broken or the transistor is a PNP type. Always holding the Red probe on the Base, shift the Black probe to the Collector: a train of short beeps should be heard. If not, the junction is broken or the transistor is a PNP type.

Placing the Red probe on the Emitter and the Black probe on the Collector should cause no output from the piezo sounder: the same should occur when reversing the probes. On the contrary, if an almost continuous beep is heard, the transistor is dead.

PNP Silicon Transistors:

Place the Black probe on the Base and the Red probe on the Emitter: a train of short beeps should be heard. If not, the junction is broken or the transistor is a NPN type. Always holding the Black probe on the Base, shift the Red probe to the Collector: a train of short beeps should be

heard. If not, the junction is broken or the transistor is a NPN type.

Placing the Red probe on the Emitter and the Black probe on the Collector should cause no output from the piezo sounder: the same should occur when reversing the probes. On the contrary, if an almost continuous beep is heard, the transistor is dead.

Darlington Transistors:

The procedure is similar to that adopted for common transistor types. The main difference is that when testing the Base - Emitter junction, you will hear the train of short beeps even after reversing the probes. This occurs because a couple of resistors is always present across either junction of the two internal transistors forming a Darlington device.

The second difference is due to the fact that an internal diode connected across Emitter and Collector (Anode to Emitter and Cathode to Collector) is always present in these devices. Therefore, with a NPN device, placing the Red probe on the Emitter and the Black probe on the Collector you will hear the usual train of short beeps, but when the probes are reverted there will be no output from the piezo sounder. On the contrary, if an almost continuous beep is heard, the transistor is dead.

PNP devices of this type are tested reversing the probes, as explained above for common transistors. Please note that when testing the Base - Emitter junction the beeps will be shorter compared to common transistors. This is caused by the fact that two junctions in series are to be measured when testing Darlingtons.

FETs:

The testing procedure is the same as that adopted for NPN silicon transistors (N-Channel FETs) or PNP silicon transistors (P-Channel FETs). The only difference is shown when checking Source - Drain connections (corresponding to Emitter - Collector): a faint, blurring sound will be heard if the device is good, even reversing the probes.

MosFets:

These devices cannot be thoroughly tested with this tool, but a MosFet in good condition should cause no beep to be heard when testing all junctions as explained above for common transistors. But the usual train of beeps will be emitted when checking the Source - Drain connection, placing the Red probe on the Source and the Black probe on the Drain of a N - Channel device, because the presence of an internal diode, as explained above for Darlington transistors.

Germanium Transistors:

Use the same testing procedure adopted for silicon transistors. The beeps forming the train will last longer than when testing silicon devices: this is due to the lower junction resistance of germanium devices in respect to silicon types.

Silicon Diodes:

Place the Red probe on the Anode and the Black probe on the Cathode: a train of short beeps should be heard. Reversing the probes no beep will be emitted.

Schottky Barrier Diodes:The same as above, but the beeps should last longer.

Germanium Diodes:The same as for Schottky Barrier Diodes.

SCRs and TRIACs:

These devices cannot be tested thoroughly, unless they are shorted: in this case an almost continuous beep will be heard. But this circuit can be useful to distinguish a SCR from a TRIAC.Placing a probe on the Gate and the other probe on the Cathode or, more properly, the MT1 pin of a TRIAC, the Tester will emit the usual train of beeps, even reversing the probes. When testing a SCR, the train of beeps will occur when the probes are placed in one way and not when reversed.

Invisible Broken Wire Detector

Portable loads such as video cameras, halogen flood lights, electrical irons, hand drillers, grinders, and cutters are powered by connecting long 2- or 3-core cables to the mains plug. Due to prolonged usage, the power cord wires are subjected to mechanical strain and stress, which can lead to internal snapping of wires at any point. In such a case most people go for replacing the core/cable, as finding the exact location of a broken wire is difficult.

In 3-core cables, it appears almost impossible to detect a broken wire and the point of break without physically disturbing all the three wires that are concealed in a PVC jacket. The circuit presented here can easily and quickly detect a broken/faulty wire and its breakage point in 1-core, 2-core, and 3-core cables without physically disturbing wires. It is built using hex inverter CMOS CD4069.

Gates N3 and N4 are used as a pulse generator that oscillates at around 1000 Hz in audio range. The frequency is determined by timing components comprising resistors R3 and R4, and capacitor C1. Gates N1 and N2 are used to sense the presence of 230V AC field around the live wire and buffer weak AC voltage picked from the test probe. The voltage at output pin 10 of gate N2 can enable or inhibit the oscillator circuit.

When the test probe is away from any high-voltage AC field, output pin 10 of gate N2 remains low. As a result, diode D3 conducts and inhibits the oscillator circuit from oscillating. Simultaneously, the output of gate N3 at pin 6 goes ‘low’ to cut off transistor T1. As a result, LED1 goes off. When the test probe is moved closer to 230V AC, 50Hz mains live wire, during every positive half-cycle, output pin 10 of gate N2 goes high.

Thus during every positive half-cycle of the mains frequency, the oscillator circuit is allowed to oscillate at around 1 kHz, making red LED (LED1) to blink. (Due to the persistence of vision, the LED appears to be glowing continuously.) This type of blinking reduces consumption of the current from button cells used for power supply. A 3V DC supply is sufficient for powering the whole circuit.

Circuit diagram:

Invisible Broken Wire Detector Circuit Diagram

AG13 or LR44 type button cells, which are also used inside laser pointers or in LED-based continuity testers, can be used for the circuit. The circuit consumes 3 mA during the sensing of AC mains voltage. For audio-visual indication, one may use a small buzzer (usually built inside quartz alarm time pieces) in parallel with one small (3mm) LCD in place of LED1 and resistor R5. In such a case, the current consumption of the circuit will be around 7 mA.

Alternatively, one may use two 1.5V R6- or AA-type batteries. Using this gadget, one can also quickly detect fused small filament bulbs in serial loops powered by 230V AC mains.The whole circuit can be accommodated in a small PVC pipe and used as a handy broken-wire detector. Before detecting broken faulty wires, take out any connected load and find out the faulty wire first by continuity method using any multimeter or continuity tester.

Then connect 230V AC mains live wire at one end of the faulty wire, leaving the other end free. Connect neutral terminal of the mains AC to the remaining wires at one end. However, if any of the remaining wires is also found to be faulty, then both ends of these wires are connected to neutral. For single-wire testing, connecting neutral only to the live wire at one end is sufficient to detect the breakage point.

In this circuit, a 5cm (2-inch) long, thick, single-strand wire is used as the test probe. To detect the breakage point, turn on switch S1 and slowly move the test probe closer to the faulty wire, beginning with the input point of the live wire and proceeding towards its other end. LED1 starts glowing during the presence of AC voltage in faulty wire. When the breakage point is reached, LED1 immediately extinguishes due to the non-availability of mains AC voltage.

The point where LED1 is turned off is the exact broken-wire point. While testing a broken 3-core rounded cable wire, bend the probe’s edge in the form of ‘J’ to increase its sensitivity and move the bent edge of the test probe closer over the cable. During testing avoid any strong electric field close to the circuit to avoid false detection.

Live Line Detector-Indicator

Detects the presence of a live mains conductor, Minimum parts counting

If the unit is brought close to a live conductor (insulated, and even buried in plaster) capacitive coupling between the live conductor and the probe clocks the counter, and causes the LED to flash 5 times per second, because the 4017 IC divides the mains 50Hz frequency by 10. When remote from a live line, the unit stops counting, the LED resulting permanently off.

Circuit diagram:

Live-Line Detector Circuit Diagram

Parts:

P1 = SPST PushbuttonD1 = Red LED (any type)C1 = 100nF 63V Polyester or Ceramic CapacitorB1 = 3V Battery (two 1.5V AA or AAA cells in series etc.)IC1 = 4017 Decade counter with 10 decoded outputs ICSensing probe 3 to 15 cm. long, stiff insulated piece of wire

Notes:

Sensitivity can be varied using a more or less long sensing probe. Due to 3V operation, the LED's current limiting resistor can be omitted.

Cable Tester Uses Quad Latch

This circuit was designed to allow microphone cables or other cables to be easily tested for intermittent breaks that can often be difficult to find using a multimeter. The circuit can test cables with up to four cores. Both switches used in the circuit are momentary contact push-buttons and it can run from a 9V battery, in which case the 7805 regulator can be omitted. To test a cable, connect it between the two sockets and press switch S2 which resets all four latches in IC1, setting them low. This turns on all four LEDs.

Circuit diagram:

Cable Tester Circuit Diagram

A good connection for each core of the cable will mean that the relevant Set inputs of the latches (pins 3, 7, 11 & 15) will be pulled high and the appropriate LED will remain on. A broken connection in the cable will result in the relevant Set input being pulled low by the associated 10kΩ resistor and the so the LED will be off. Because the circuit latches, it is easy to pinpoint even the smallest breaks by simply flexing and twisting the cable up and down its length until one of the LEDs turns off. To test different types of cables, simply connect appropriate sockets in parallel with or in place of the XLR sockets.

High Side Current Measurements

It’s always a bit difficult to measure the current in the positive lead of a power supply, such as a battery charger. Fortunately, special ICs have been developed for this purpose in the last few years, such as the Burr-Brown INA138 and INA168. These ICs have special internal circuitry that allows their inputs to be connected directly to either end of a shunt resistor in the lead where the current is to be measured. The shunt is simply a low-value resistor, across which a voltage drop is measured whenever a current flows. This voltage is converted into an output current Io by the IC.

This current can be used directly, or it can be converted into a voltage by means of a load resistor RL. In the latter case, the ‘floating’ measurement voltage across the shunt is converted into a voltage with respect to earth, which is easy to use. The value of RL determines the gain. A value of 5 kΩ gives 1×, 10 kΩ gives 2×, 15 kΩ gives 3× and so on. It all works as follows. Just like any opamp, this IC tries to maintain the same potential on its internal plus and minus inputs. The minus input is connected to the left-hand end of the shunt resistor via a 5-kΩ resistor.

When a current flows through the shunt, this voltage is thus lower than the voltage on the plus side. However, the voltage on the plus input can be reduced by allowing a small supplementary current to flow through T1. The IC thus allows T1 to conduct just enough to achieve the necessary lower voltage on the plus input. The current that is needed for this is equal to Vshunt / 5 kΩ. This transistor current leaves the IC via the output to which RL is connected. If the value of RL is 5 kΩ, the resulting voltage is exactly the same as Vshunt. The IC is available in two versions.

The INA138 can handle voltages between 2.7 and 36 V, while the INA168 can work up to 60 V. The supply voltage on pin 5 may lie anywhere between these limits, regardless of the voltage on the inputs. This means that even with a supply voltage of only 5 V, you can make measurements with up to 60 V on the inputs! However, in most cases it is simplest to connect pin 5 directly to the voltage on pin 3. Bear in mind that the value of the supply voltage determines the maximum

value of the output voltage. Also, don’t forget the internal base-emitter junction voltage of T1 (0.7 V), and the voltage drop across the shunt also has to be subtracted.