Cable Tester

This cable tester allows you to quickly check audio cables for broken wires. Because of the low power supply voltage, batteries can be used which makes the circuit portable, and therefore can be used on location.

Cable Tester Circuit diagram:

The design is very simple and well organ-ised: using the rotary switch, you select which conductor in the cable to test. The corresponding LED will light up as indication of the selected conductor. This is also an indication that the power supply volt-age is present. If there is a break in the cable, or a loose connection, a second LED will light up, corresponding to the selected conductor. You can also see immediately if there is an internal short circuit when other than the corresponding LEDs light up as well.

You can also test adapter and splitter cables because of the presence of the different connectors.

Two standard AA- or AAA- batteries are sufficient for the power supply. It is recommended to use good, low-current type LEDs. It is also a good idea not to use the cheapest brand of connectors, otherwise there can be doubt as to the location of the fault. Is it the cable or the connector.

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Simple Wire Continuity Tester by LM709

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.

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Simple Logic Tester Circuit

The tester shows on a seven-segment, common-cathode display whether its input is logic 1 (H on the display) or logic 0 (L on the display).
An undefined level is indicated as “n’. When the input is low, T1 is switched off and T2 and T3 conduct. This results in a high output at ICM and a low one at lC lb, whereupon segment ‘d` lights. Together with permanently actuated segments ‘e’ and ‘t` , this causes an “L’ to be displayed. When the input is high, This on and T2 and T3 are off. The output of Cla is then low and that of ICH, is high. Apart from segments ‘e‘ and ‘t` , ‘b’, `c`, and‘g’ also light, which causes an H to be displayed. When the input is undefined. or open, all transistors are on (because of Rl, R2 and R3). The outputs of ICM and ICH, are then both high, which causes segments A ‘a’, ‘b‘ and ‘c’ to light together with ‘e’ and ‘f; an ‘n’ (no level) is then displayed. The buzzer is not essential, merely use ful; it may thus be omitted. If it is used, it should be a type with integral oscillator.

The type of the components used is not critical. The display may be any seven segment, common-cathode type. IC] may be a standard 7400 or an LS version of this or the open-collector version 7401; HC and HCT types are less suitable because these cannot provide the required output current.  The switching thresholds of the tester are at 1 V and 3 V, which is not standard, but in practice they do well. The 3 V threshold may be lowered slightly by increasing the value of R4. The input impedance of the tester is 5 kQ, which has no effect on the circuit on test. V  The current drawn by the tester is determined by the type of display; in the prototype, it is about 60 mA.

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