What's this thing?
A versatile quadruple low voltage tester, contributing to a greener world because with the help of this little gadget a lot of broken electronic devices can get a second or third life, and will not be sent to the garbage dump !

Safety warning:
Be careful whatever you test, the device can only be used to test apparatus with safe low voltage inside.

Never use it to connect to dangerous voltages !

Step 1: Repair Café

Where is the best place to use this quadruple tester? At the Repair Café !

A Repair Café is a meeting in which people repair household electrical and mechanical devices, computers, bicycles, clothing, etc. They are organised by and for local residents. Repair Cafés are held at a fixed location where tools are available and where they can fix their broken goods with the help of volunteers. Its objectives are to reduce waste, to maintain skills around repairs and to strengthen social cohesion.

Step 2: How to Build the Audio Amplifier

Parts list for this amplifier:

1 Velleman kit type K4001
1 potentiometer 10 kOhm
1 knob for the potentiometer
1 resistor 100 kOhm 1/8 Watt
1 resistor 100 Ohm 1/8 Watt

The audio amplifier is a K4001 kit from Velleman, a 7 Watt mono amplifier.
Follow this link and you will find all neccessary details. (assembly instructions, parts list etc).

http://www.vellemanusa.com/products/view/?id=350529

As shown in the circuit diagram, I added a 100 Ohm resistor on the output to limit the power for the earbuds I used, (they do not need 7 Watt). And I added a potentiometer (10kOhm) and a series resistor of 100 kOhm on the input to adjust the audio level and limit the influences of the amplifier on the test object.
Finally I removed a few mm from the top of the black metal heatsink, else the amplifier would not fit into the plastic box.

Step 3: How to Build the Audio Signal Generator

Parts list for this signal generator:

1 small part prototype PCB
2 resistors 47 kOhm1/8 Watt
1 resistor 100 kOhm 1/8 Watt
2 capacitor 10 nF
1 capacitor 10 uF
1 IC type NE555

This generator generates a small block type signal with a frequency of appr. 1 kHz, you can use it to send into a test object and follow the signal via the amplifier part of the tester.

You can find a lot of NE555 applications on the instructables website, just search for 555 to find a zillion examples..
See this link :
http://www.talkingelectronics.com/te_interactive_index.html

Step 4: How to Build the Wiring Tester and the LED Tester

Parts list for this wiring tester and LED tester:

2 resistors 1 Mohm 1/8 Watt
1 resistor 100 kOhm 1/8 Watt
3 resistors 1 kOhm 1/8 Watt
1 resistor 10 kOhm
1 green LED 5 mm
1 red LED 5 mm
1 buzzer 9V DC
1 capacitor 10 nF
1 ON/OFF switch
1 battery 9V
1 transistor BC547 (NPN)
1 transistor BF472 (PNP)
1 small part prototype PCB

The wiring tester is a very sensitive and high impedance detector and will light the green LED (via the BF472 transistor) when the input is connected to GND.
It has a second little amplifier (the BC547 transistor) to activate the buzzer.
The tester has a additional 1 kOhm resistor, connected to the VCC 9V DC to test LED's. A LED can be connected between this resistor (connected to the white input plug) and GND (connected to the black input plug).

Step 5: Building It All Together

Parts list:
1 plastic box
5 female plugs for 6 mm banana plugs (red, green, white, blue, black)
1 female plug for 3.5 mm stereo earbud connection
. wiring

Build the three separate circuits (amplifier, wiring tester and signal generator) into a small plastic box.

Connect the following plugs for 6 mm banana plugs on one side:
RED: audio IN
WHITE: LED test
BLUE: Wiring test
GREEN: Audio signal out
BLACK: Ground
On one other side you can connect a 3.5 mm plug for the connection of the earbuds on the audio amplifier.

To switch the quadruple tester ON and OFF place the ON/OFF switch on one side together with the red ON/OFF status LED.

On the front the knob for the audio level potentiometer is placed, together with the buzzer and the green wiring detection led.

Step 6: What Can You Test?

What can you test?

Via the blue connector:
Wiring ! You can test all types of electrical connections.
Basically it is a high impedance resistance tester with a buzzer and a green LED to detect failing copper connections on printed circuit boards and failing wiring.
Because it beeps very loud you can keep your eyes on the test location.

Via the white connector: LED !
Nearly all types of LED can be tested without worrying about serial resistors.
It is a 9 Volt DC connection with a serial resisor of 1000 Ohm.

Via the red connector:
Sounds! Here you can listen to electric signals inside the device you are testing, with your little earphones.

Via the green connector:
Audio test signal.
Here you have an audio test signal (block type) for example to test a circuit with amplifiers.

The black connector:
Ground connection.