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In this schematic circuit is presented a very simple Zener Diode Tester circuit that require few external components to  be build . Zener Diode Tester Circuit diagram As you can see in the schematic circuit , the Zener Tester  project is based on a common 741 operational amplifier .The supply need only be as high a value as the zener itself . The variable resistor P can be calibrated ( in volts ) , so when the LED 1 lights the voltage on pins 2 and 3 of the 741 operational amplifier is nearly equal .

Why a lamp tester or fuse tester? Testing cables, wires, lamps… belongs to a repair job and sometimes this becomes too cumbersome since one has only two hands and too often, one has to hold the part being tester and the two probes of an ordinary continuity tester all at the same time. This fuse and lamp tester enables easy testing of lamps and fuses by using the conductivity of the human body. One of the test probes is connected to the part under test while the other probe is hel dby the normal hand. Lamp and Fuse Tester Circuit Diagram When the lamp or fuse is working properly, your eyes will glow in the dark! Just kidding :) . When the lamp or fuse is working properly, a small amount of current flows through the hand which is enough to switch the transistors and light the LED. 

555 timer tester is a simple circuit that serves to test the condition of IC 555. 555 timer circuit tester, in principle, start the timer 555 in astable multivibrator mode. As an indicator of the status of the timer 555 good condition or damaged to use 2 pieces LED which will light up in a blink alternately when the timer 555 in good condition. And only one will turn on or off all the timer 555 when the condition is broken. 555 timer circuit tester is powered using 9 Volt DC voltage source. Complete circuit tester 555 as follows.   How to use 555 timer tester is in conjuction with IC 555 to test the existing IC socket according to the order button. Then activate the power switch to begin testing the 555 timer ic. Then live we observe the LED indicators 2 before, whether flashing alternately (good) or not blink or even die all (timer 555 damaged). source:link

The circuit can be simply Q1 is connected as a current source. By D1, there is a constant voltage on the base, and it is worth considering the selected resistor in the emitter approximately 5.6 V. With an emitter resistor of 5K6 R2 will then 1mA through the transistor. With the chosen resistors in the circuit the current is approximately: 1mA, 2mA, 5mA, 10mA and 20mA. Great precision is not required. If meter is chosen here for a small DVM module. However, every other meter is applicable, provided that the input resistance is high enough. Construction: The circuit is simple to build on a piece of PCB holes. Note that the DVM module separate from the circuit galvanic isolated power supply needs. Using Connect the test zener diode between the terminal A and K. Start with a current of 2mA. This is a safe value for most type zener diodes. Depending on the type of zener diode, may be chosen for a greater current. Than the Zener voltage will vary slightly. Join the zener diode on backwards, ...

You have to admit that these tiny electronic lamps are handy, and they last almost forever. Around 40 years after Nick Holanyak developed the first LED, they have become just about indispensable. Any self-respecting electronics hobbyist always has a few in his junk box. But before you use LEDs, it’s a good idea to check them out. With a LED tester, you can even do it in the dark! LEDs are available nowadays in all shapes and colors. There are types with clear, colorless packages, while others have colored plastic packages. Many modern types of LEDs need less current than older types. Some of them provide quite a puddle of light if you give them a decent amount of current. When you’re working with used LEDs from the junk box, there’s a good chance that you can’t tell which lead is which any more. (If the leads haven’t been trimmed, the short lead is always the cathode lead and the long lead is the anode lead.) If you use several LEDs in a display where they all have the same current you...

Description This circuit enables you to test quartz resonators at the range values from 32kHz to 24MHz. Confirmation of good state of quartz resonator is done by diode signalling LED and acoustic signal. Switch S2 enables change of range . Circuit Diagram Parts R1,R7 1 M R2,R3 5,6 k R4 220 K R5 1 k R6 220 C1,C2 220 pF C3,C4 10 F/25V RSM C5 100 nF C6,C7 33 pF D1 LED 5 mm, yellow D2 1N4148 T1 BC547C IO1 4060 IO2 74HC4060 IO3 78L05 S1 push button (normally open) S2 Two-positional switch  Layout Source -http://www.elektroda.pl/

This tiny conductivity tester works with LM 3909. The tester makes a beeping sound if the resistance between the test probes between 0 and 100 O lies. Due to the volume of the beep, the resistance between the test probes can be determined. Audio Lm 3909 IC-conduction tester Circuit Diagram Parts List      R1 = 1 k      C1 = 10 uF      C2 = 100 nF      LS = Loudspeaker 12 to 16 Ω      IC1 = LM 3909

D. Mohan Kumar know as his best creations. For beginners, here’s a low-cost multitester that can be used to test the condition of almost all the electronic components For beginners, here’s a low-cost multitester that can be used to test the condition of almost all the electronic components from resistors to ICs. It uses only a few components but can also detect polarity, continuity, logic states and activity of multivibrators. The circuit is extremely simple and exploits the biasing property of bipolar transistors. Transistors T1 and T2 act as transistor switches driving the red and green halves of bicolour LED1 independently to give results of the test.  Simple Handy Tester Circuit Diagram When power is applied by pressing switch S1, transistor T1 stops conducting due to the lack of forward bias. At the same time, transistor T2 takes base bias voltage from the battery through resistor R1 and conducts. This allows the red half of bicolour LED1 to illuminate. When the base of trans...

While detecting discontinuities on a circuit board, it is probable to include resistors, semiconductors or other elements in measurements. This situation may cause wrong results. On the other hand sometimes the voltage or current of the multimeter may defect some circuit components. Our circuit overcomes this inconvenient conditions. The circuit determines greater than 1 ohm values as discontinuity. Measure voltage is not more than 2mV. So no kind of diode, IC or other component is bypassed. Maximum current output of the circuit is about 200uA. Simple Wire Continuity Tester by LM709  Indicator of the circuit is a LED. Voltage supply may be two 9 Volt batteries. Voltage adjustment of the amplifier is done by P1 potentiometer. To do this process, first short circuit the probes and then turn P1 until LED brights. When you separate the probes again LED will fade out. This is a cheap and very useful circuit. You can build it on a PCB to use more easily.

This tester is primarily meant to test bipolar transistors. It can indicate the type of the transistor as well as identify its base, collector and emitter pins. The circuit is very simple. The direction of current flow from the terminals of the transistor under test (TUT) is indicated by a pair of LEDs (green-red). An npn transistor produces a red-green-red glow, while a pnp transistor produces a green-red-green glow, depending on the test point that connects to the terminal of the transistor. Emitter and collector are differentiated by pressing pushbutton switch S1 that actually increases the supply voltage of the circuit by about 5.1V. At the heart of the circuit is IC CD4069 (IC3), which oscillates and produces pulses required to test a pair of transistor leads for conduction in both the directions. Different combinations are selected by an arrangement of counter CD4040 (IC1) and bilateral switch CD4016 (IC2). Fig. 1 shows the circuit of the bipolar transistor tester. A pair of LEDs...