Posts Tagged ‘mains voltage tester’

Components Voltage Tester Circuit Schematic

This simple circuit tests speakers, microphones, transformers and voltage. It’s basically a very low frequency oscillator that produces extremely short ‘fruity’ pulses. The type of sound produced is very easy to hear and to determine the precise direction it is coming from, thus making it ideal for checking the phasing in multiple speaker installations. It is also very useful for car stereo installations as well as public address systems where it can drive dozens of speakers directly on a 100V or 70V line system.

The signal is also easy to hear on a public address system so that you can drive around a large installation with the window down and easily hear each speaker as you drive past. It is easy to check that a speaker is in phase with its neighbours, by listening for the artificial centre created between two identical sound sources. Q1 and Q2 oscillate when connected to loads between zero and about 1000O. The frequency increases as the resistance of the load increases – loads produce about 8Hz output while 100O loads will produce about 100Hz output, although it is only approximate.

The unit is also useful for checking dynamic microphones (not condenser types), headphones, transformers (both audio and mains) and resistance loads (only visual checks via the LED). The pulses produced can sound too loud for some delicate circuits such as dynamic microphones and headphones, but the pulse is so short that it is virtually impossible to do any damage; the average current flow is only a few milliamps.

The circuit needs no power switch as the oscillator only operates when the negative side of the battery is connected through the load being tested. The LED flashes at each pulse as a visual indication that the load is lower than about 1000O. The circuit works from a 3V battery pack. To use a 9V battery change the 15O resistor to 47O, the 1.8O resistor to 5.6O and the .033µF capacitor to .01µF. LED2, diode D3, zener diode ZD1 and the series 220O resistor form a voltage indicator which is used to detect and indicate any voltage greater than about 10V.

LED2 only illuminates if the voltage rises above the threshold set by ZD1 and D1, which is more than the battery voltage (3V or 9V). These components can be omitted if the device is not going to be used for working on cars. However, it’s quite handy having a device that can check power wires, shorts to chassis and speakers in a car.

Parts:
R1 = 5.6M
R2 = 1.8R
R3 = 15R
R4 = 220R
Q1 = BC327
Q2 = BC337
D1 = Green LED
D2 = Red LED
D3 = 1N4148
Z1 = 6.8V Zener
C1 = 0.033uF
B1 = 3V Battery
read more : http://www.extremecircuits.net/2010/01/components-voltage-tester-circuit.html

AC Line testing circuit.

This circuit will detect AC line currents of about 250 mA or more without making any electrical connections to the line. Current is detected by passing one of the AC lines through an inductive pickup (L1) made with a 1 inch diameter U-bolt wound with 800 turns of #30 – #35 magnet wire. The pickup could be made from other iron type rings or transformer cores that allows enough space to pass one of the AC lines through the center. Only one of the current carrying lines, either the line or the neutral should be put through the center of the pickup to avoid the fields cancelling. I tested the circuit using a 2 wire extension cord which I had separated the twin wires a small distance with an exacto knife to allow the U-bolt to encircle only one wire.

The magnetic pickup (U-bolt) produces about 4 millivolts peak for a AC line current of 250 mA, or AC load of around 30 watts. The signal from the pickup is raised about 200 times at the output of the op-amp pin 1 which is then peak detected by the capacitor and diode connected to pin 1. The second op-amp is used as a comparator which detects a voltage rise greater than the diode drop. The minimum signal needed to cause the comparator stage output to switch positive is around 800 mV peak which corresponds to about a 30 watt load on the AC line. The output 1458 op-amp will only swing within a couple volts of ground so a voltage divider (1K/470) is used to reduce the no-signal voltage to about 0.7 volts. An additional diode is added in series with the transistor base to ensure it turns off when the op-amp voltage is 2 volts. You may get a little bit of relay chatter if the AC load is close to the switching point so a larger load of 50 watts or more is recommended. The sensitivity could be increased by adding more turns to the pickup.

source : http://ourworld.compuserve.com/homepages/Bill_Bowden/

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