This article details an AC-based continuity tester designed for frontline test and repair jobs. The circuit provides a simple GO/NO-GO test for localizing faults in multicore cables. Open circuits are more likely at connector ends. By identifying the faulty end, the AC continuity tester allows you to open and repair the correct cable end. This action avoids the risk of damaging a good connector by opening it up. This approach is also useful for testing an installed cable with ends at different locations.
The schematic illustrates a circuit for a continuity tester that injects an AC signal on one cable wire and then looks for the absence of capacitive coupling on the other wires. One end of a bad cable typically shows good AC continuity, while the other end typically has one or more connector pins with no AC continuity. Because a short in the cable appears as a good connection, the operator can easily confirm that the tester is operating correctly by simply shorting its test leads together.
The left side of the circuit uses a low-power dual comparator (MAX9022) to form a relaxation oscillator operating at approximately 155kHz. It produces a peak-to-peak output signal approximately equal to the supply voltage, which is fed to a connector of the cable under test. The right side of the circuit processes any AC signal picked up by the inter-lead capacitance. That AC signal is first rectified by a pair of silicon diodes, and then integrated on storage capacitor C5. The bleed resistor (R5) provides some noise immunity and helps to reset the capacitor between tests.
The output resistor (R4) and input capacitor (C4) provide limited circuit protection. The circuit indicates OPEN for any test-cable capacitance below 100pF. (Thus, a standard 2m IEC mains test lead, whose typical lead-to-lead capacitance is 200pF, would test OK.) The circuit is also immune to false triggers caused by the 60Hz pickup from power lines.
Because the typical current draw of this low-power circuit is less than 40μA most of the time, the circuit can be powered by three AA or AAA 1.5V pencil batteries.
Many low-cost alternatives are available for the output device (e.g., a DC-activated piezoelectric buzzer), and most alternatives feature a suitably wide operating voltage range. The 100nF capacitors are standard ceramic decoupling capacitors, and the circuit contains no critical passive components. The comparator’s high-side drive is better than its low-side drive, so it should be used to source (rather than sink) current to the indicator device. Diodes D1 through D3 are silicon diodes.
AC Continuity Tester - [Link]
Tony Keith build an Arduino DMX tester, he writes:
I work part-time (more of a hobby) in the lighting industry and use DMX since it is the industry standard for communicating or controlling devices (lighting fixtures, controllers, consoles, etc..) I have seen commercial DMX testers on the market but I wanted to create my own.
I have been working on an idea to create a low cost (<$50), Arduino based DMX tester.
The tester would provide the following functionality:
Simple input protocol for entering commands using 4 X 4 (16) key pad matrix.
Support LCD display (4 x 20) Character
Output DMX for single channel or a range of channels at a set intensity level.
Arduino DMX Tester – Inexpensive Tester for Sending DMX-512 - [Link]
This project is a simple LED tester and LED polarity checker. It can be used to check 1206, 0805, 0603 and 5mm LEDs. All parts are readily available and they are very cheap. Usage is very simple. Just press the tack switch to first check the battery is good. The blue led will turn on. Now you are ready to test your leds and check their polarity.
Simple SMD LED tester - [Link]
Kevin Rye designed a simple LED tester:
I decide to put together a small LED Tester board. It’ll be powered by a small coin cell battery. I can pick up an LED with a pair of tweezers and just simply tap it to the solder pads. If it lights up, I know I’m holding it the right way, or not. As far as a PCB, I want it to be super simple and super cheap. I really don’t want to spend $10 bucks on something so simple. However, I don’t want it to be a one-trick pony either. Ideally, it should work for through-hole LEDs as well, as 1206s and whatever other sizes I can’t think of right now. Do SMD LEDs come in an 0805 package? I’ve never seen one, but it’s probably a good idea to place some large pads on it so that it’ll work for anything.
Kevin’s LED tester - [Link]
Hemal Chevli blogged about his transistor tester project:
It has mega-8 as the brain, lcd to show specs of the transistor like which pin is which, what type of transistor it is eg NPN,PNP, N-MOSFET,P-MOSFET, etc., many components can be tested like different types of transistor, diodes, resistors etc, the good thing about this is that it also shows which leg is which, no need to open the data sheet
Transistor tester project - [Link]
LEDger Led (polarity) tester:
Everytime I solder a SMD LED on a pcb I have to turn on one of my multimeters and flip it over to diode-test mode and then probe the SMD LED to see which connector is the anode and which is the cathode. The LEDger is a small PCB with a button cell battery and smd footprints that allows me to, while still holding the LED in my tweezers. just hold it onto one of the footprints and see if it lights up or not.
LEDger Led (polarity) tester - [Link]
Gadget Gangster @ instructables.com writes:
A little bigger than a postage stamp, the Simple Servo Tester lets you control two digital or analog servos without using a transmitter or receiver, just plug in your battery pack to start testing.
Use it to check your servos before installing them into your models or to center your servos when setting up linkages. The Simple Servo Tester can also be tuned to precisely center your servos – Some manufactures consider 1.520 milliseconds to be center while others use 1.500 milliseconds.
Simple Servo Tester - [Link]
Trandi made this simple DIY Servo tester based on ATTiny85:
I had to test a RC speed controller that I wanted to use to control an electric car window motor, and for the 100th time I was facing the same dilemma: find 8 batteries for my remote control, dismount the RX part from the quadcopter and use that, OR grab the Arduino and write quickly some code to generate the corresponding signals? Neither of which was actually particularly handy… So I finally decided to build a small stand alone servo tester.
DIY servo tester based on ATTiny85 - [Link]
Raju Baddi writes:
A specialized test gadget that tests continuity quantitatively in both AC and DC modes could prove to be an indispensible bench test instrument. This article describes such a continuity test set up, which provides two different display options.
The meter (see Figure 1) can be used in AC mode to test/estimate capacitors, inductors, transformers etc. that are sensitive to AC current, while the LEDs can be used in AC/DC mode to test diodes, transistors, transformers, etc.
Method tests continuity in AC and DC - [Link]
Zener diode is a special diode, unlike normal diodes zener diodes are intended to work in the breakdown voltage. These components maintain constant voltage at its terminals. This is a circuit to help you find out what’s the breakdown voltage of your diodes.
- Read Vz value of zener diode in Led display
- Zener diode tester range: 1V to 50V
- Two scales 5mA and 15mA test
Zener diode tester 1V to 50V - [Link]