## Logic Probe using NOT Gates

A very simple logic probe using NOT gates. The logic probe allows us to know the logic state of any point in a digital circuit. The signal to be measured is applied to the probe tip input.

## What is a Logic Probe?

A logic probe is a simple and inexpensive instrument contained within a pen-like tube. It has 3 LED indicators that show the status of the point under test. 5 DIY Logic Probes

## Audible Logic Probe using the 555 Timer

Many logic probes use LEDs to visually indicate the logic state of the point under test. This causes the user to have to see the point under test and the LED at the same time.

## Logic Probe with 7 Segment Display

Logic probe using 7 segment display

This logic probe with 7 segment display is designed with TTL technology and does not use LEDs to display the high and low logic levels found in many of the logical probes on the market. The circuit shows the capital letter “H” when there is a logical “1” or the letter “L” when there is a logical “0”.

## How to protect multimeter’s 500mA fuse?

How to protect the 500mA Fuse of a Multimeter?

A very simple circuit that protect the 500mA fuse of a multimeter, due to the high frequency that these are burned.

## Diode Tester Circuit using 741

This diode tester circuit checks, if the diode is in good condition and also determines its polarity. To accomplish our goal, we use an 741 operational amplifier (IC1) configured as an oscillator.

## How to Extend the Voltage Range of an Analog Multimeter?

How to extend the voltage range of an analog Multimeter? In order to extend the voltage range, a resistor is placed in series with the multimeter. Calculation example.

## Logic probe circuit using CD4001 IC

Logic probe circuit with CD4001 IC. This circuit is implemented with CMOS IC technology and is recommended for testing circuits using the same technology

## Logic Probe using two transistors

This Two Transistor Logic Probe is a very simple circuit that can be implemented using two NPN bipolar transistors (T1, T2) in a Darlington configuration.

## What is the Wheatstone Bridge Circuit?

The Wheatstone bridge circuit

This circuit  was designed in 1833 by Samuel Hunter Christie (1784-1865). However, It was Mr. Charles Wheatstone who gave many uses to the Wheatstone bridge circuit when he discovered it in 1843.

## Audible Continuity Tester

Continuity Tester with Buzzer – Works on live circuits.

This continuity tester with buzzer works on live circuits. Very important, as common continuity testers are used with the power source disconnected.

## 555 Timer Tester circuit

555 IC Tester Circuit (PCB)

This 555 IC tester circuit, allows us to make sure that this integrated circuit works properly. This same test can be achieved by operating the 555 as astable multivibrator, but this test does not allow
to observe its operation in detail.

## Op Amp Tester Circuit Diagram

Op Amp Tester Circuit Diagram

Very simple circuit to test 741 op amp or another IC with the same pin configuration. Circuit working explanation

## How to Make a Current Flow Indicator?

This Electric Current Flow Indicator gives a visual indication that there is a current flow. Possible applications for this small circuit may be: a battery charger, a voltage power source, etc.

In order to achieve our objective we place 3 rectifier diodes in series, which in turn are in series with the load / battery.

## Measuring Low Resistances

Measuring Low or very low resistances

There are cases where the resistance is too low and a direct use of the ohmmeter is not practical. So a special method is needed

## Continuity tester using 741 IC

Continuity tester using 741 operational amplifier that operates as a differential amplifier.

A good application for this circuit would be to test welds made on a printed circuit board. It could also be used to test continuity of wires, connections, etc.

## How to Measure Beta of a Transistor?

How to Measure Beta of a Transistor? (β / hfe of transistor)

The beta (β) is a characteristic of each transistor. This feature is found in the NTE, ECG manuals, etc. These manuals have a minimum or approximate values of the real values. This means that we do not know the real value of the transistor.

## Resistance measurement of delicate components

How to measure the resistance of a delicate or sensitive component?

There is a special way of resistance measurement when the component to be measured is very sensitive or delicate.