Showing posts with label tester. Show all posts
Showing posts with label tester. Show all posts
Tuesday, December 24, 2013
Universal Tester for 3 pin Devices
Most 3-terminal active components can be tested statically using just an ohmmeter. But when you have a lot of these devices to test, the procedure soon becomes boring. That’s where the idea came from to combine fast, easy testing for these types of device into a single instrument.
The unit described here enables you to test NPN and PNP bipolar transistors, N-or Pchannel FETs or MOSFETs, UJTs, triacs, and thyristors. Regardless of the type of device, the tests are non-destructive. Universal connectors allow testing of all package types, including SMDs (up to a point). The unit lets you change from one type of device to another in a trice. It avoids using a multi-pole switch, as they’re too expensive and hard to find.
Here’s how to build a versatile instrument at a ridiculously low cost. IC1 is a 4066 quad CMOS switch which will let us switch between bipolar transistors and FETs. LEDs D1–D4 tell us about the condition of the test device, when we press the ‘Test’ button. The 4066 can only handle a few milliamps, not enough for the other component types to be tested, hence the reason for using relay RE1. This 12 V relay offers two NO contacts. The first applies power to the UJT test circuit, the second applies it to the triac and thyristor test circuit.
Extensive testing has shown that the best way to test UJT transistors is to do so dynamically, with the help of a relaxation oscillator. Net-work R11/C1 sets the oscillator frequency to around 2 Hz. On pin B1 of the UJT we find a nice sawtooth, which is not of much interest to us here. However, pin B2 gives good but very short pulses. IC2, wired as a monostable, lengthens these pulses so they can be clearly seen via LED D5.
The relay’s second pole is going to drive the thyristor’ sortriac’s trigger pin. The value of R18 is a good compromise with respect to the varying trigger currents for this type of device. Resistor R17 is important, as the hold-ing current must be high enough for a triac; 250 mA is a good compromise. LED D6 tells you if the device is in good condition or not; but watch out, the test result must be con-firmed by briefly cutting the power in order to reset the triac.
On the web page for this article [1] you’ll find the author’s CAD files (PCB layout and front panel) along with some photos of his project. On the prototype, the LEDs and the ‘Test’ button were wired onto the copper side of the PCB. The six female connectors for the devices being tested were salvaged, but there are lots of models available on the market (the pitch is standard). The test cable crocodile clips must be as small as possible for testing SMD devices.
Source : http://www.ecircuitslab.com/2012/05/universal-tester-for-3-pin-devices.html
Saturday, October 5, 2013
Connection Tester
A low resistance ( 0.25 - 4 ohm) continuity tester for checking soldered joints and connections.
This simple circuit uses a 741 op-amp in differential mode as a continuity tester. The voltage difference between the non-inverting and inverting inputs is amplified by the full open loop gain of the op-amp. Ignore the 470k and the 10k control for the moment, and look at the input of the op-amp. If the resistors were perfectly matched, then the voltage difference would be zero and output zero. However the use of the 470k and 10k control allows a small potential difference to be applied across the op-amp inputs and upset the balance of the circuit. This is amplified causing the op-amp output to swing to full supply voltage and light the LEDs.
Setting Up and Testing:The probes should first be connected to a resistor of value between 0.22 ohm and 4ohm. The control is adjusted until the LEDs just light with the resistance across the probes. The resistor should then be removed and probes short circuited, the LEDs should go out. As the low resistance value is extremely low, it is important that the probes, (whether crocodile clips or needles etc) be kept clean, otherwise dirt can increase contact resistance and cause the circuit to mis-operate. The circuit should also work with a MOSFET type op-amp such as CA3130, CA3140, and JFET types, e.g. LF351. If the lEDs will not extinguish then a 10k preset should be wired across the offset null terminals, pins 1 and 5, the wiper of the control being connected to the negative battery terminal.
Friday, October 4, 2013
Three State Continuity Tester
The continuity tester can distinguish between high-, medium-, and low-resistance connections. When there is a conductance between the inputs, which are linked to small probes, a current flows from the +9 V line to earth via R1 and R2. The consequent potential difference, p.d., across R2 is used to determine the transfer resistance. Operational amplifier IC1c amplifies the p.d. across R2 to a degree that is set with P1. A window comparator, IC1a and IC1b, likens the output of IC1c to the two levels set with potential divider R4–R6. Depending on the state of the outputs of the two comparators, three light-emitting diodes (LEDs) are driven via the gates and inverters contained in IC3 and IC2 respectively in such a way that they indicate the transfer resistance in three categories.
When the resistance is high, green diode D3 lights; when it is of medium value, yellow diode D2 lights, and when it is low, red diode D1 lights. The levels at which the diodes light is set with P1, but note that in any case the minimum value depends on the p.d. across R2. It is possible to reduce the value of the p.d. to enable lower transfer resistances to be detected, but this would mean an increase in the test current through R2. With values as specified, the circuit in its quiescent state draws a current of about 17 mA, but in operation each LED adds about 10 mA to this. The LM324 (IC1) may be operated from a single supply line: R1 prevents the voltage at the input from reaching the level of the supply line (which is not permissible). The supply voltage may be 5–18 V. The LEDs are driven directly by the inverters in the 4049 (IC2), which can switch currents of up to 20mA to earth.
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When the resistance is high, green diode D3 lights; when it is of medium value, yellow diode D2 lights, and when it is low, red diode D1 lights. The levels at which the diodes light is set with P1, but note that in any case the minimum value depends on the p.d. across R2. It is possible to reduce the value of the p.d. to enable lower transfer resistances to be detected, but this would mean an increase in the test current through R2. With values as specified, the circuit in its quiescent state draws a current of about 17 mA, but in operation each LED adds about 10 mA to this. The LM324 (IC1) may be operated from a single supply line: R1 prevents the voltage at the input from reaching the level of the supply line (which is not permissible). The supply voltage may be 5–18 V. The LEDs are driven directly by the inverters in the 4049 (IC2), which can switch currents of up to 20mA to earth.Monday, September 30, 2013
Simple But Reliable Car Battery Tester
This circuit uses the popular and easy to find LM3914 IC. This IC is very simple to drive, needs no voltage regulators (it has a built in voltage regulator) and can be powered from almost every source. This circuit is very easy to explain: When the test button is pressed, the Car battery voltage is feed into a high impedance voltage divider. His purpose is to divide 12V to 1,25V (or lower values to lower values).
This solution is better than letting the internal voltage regulator set the 12V sample voltage to be feed into the internal voltage divider simply because it cannot regulate 12V when the voltage drops lower (linear regulators only step down). Simply wiring with no adjust, the regulator provides stable 1,25V which is fed into the precision internal resistor cascade to generate sample voltages for the internal comparators. Anyway the default setting let you to measure voltages between 8 and 12V but you can measure even from 0V to 12V setting the offset trimmer to 0 (but i think that under 9 volt your car would not start).
There is a smoothing capacitor (4700uF 16V) it is used to adsorb EMF noise produced from the ignition coil if you are measuring the battery during the engine working. Diesel engines would not need it, but Im not sure. If you like more a point graph rather than a bar graph simply disconnect pin 9 on the IC (MODE) from power. The calculations are simple (default)
For the first comparator the voltage is : 0,833 V corresponding to 8 V
* * * * * voltage is : 0,875 V corresponding to 8,4 V
for the last comparator the voltage is : 1,25 V corresponding to 12 V
Have fun, learn and dont let you car battery discharge... ;-)
This solution is better than letting the internal voltage regulator set the 12V sample voltage to be feed into the internal voltage divider simply because it cannot regulate 12V when the voltage drops lower (linear regulators only step down). Simply wiring with no adjust, the regulator provides stable 1,25V which is fed into the precision internal resistor cascade to generate sample voltages for the internal comparators. Anyway the default setting let you to measure voltages between 8 and 12V but you can measure even from 0V to 12V setting the offset trimmer to 0 (but i think that under 9 volt your car would not start).
There is a smoothing capacitor (4700uF 16V) it is used to adsorb EMF noise produced from the ignition coil if you are measuring the battery during the engine working. Diesel engines would not need it, but Im not sure. If you like more a point graph rather than a bar graph simply disconnect pin 9 on the IC (MODE) from power. The calculations are simple (default)
For the first comparator the voltage is : 0,833 V corresponding to 8 V
* * * * * voltage is : 0,875 V corresponding to 8,4 V
for the last comparator the voltage is : 1,25 V corresponding to 12 V
Have fun, learn and dont let you car battery discharge... ;-)
author: Jonathan Filippi
e-mail: jonathan.filippi@virgilio.it
e-mail: jonathan.filippi@virgilio.it
Saturday, August 31, 2013
Digital AC DC Voltage Tester Circuit
Description
It is always necessary for engineers and technicians to test AC/DC mains voltages and continuity for any given circuit during breakdowns, the above mentioned circuit can be used as and sought of tester and can also check the continuity for you. all one has to do is that to touch the two probes at the required terminal of either live or an dead circuit
The unique design of the tester allows the circuit to work in both AC and DC without any mode selector switch.
When the probes A and B are short circuited voltage pin 1 goes a little below the threshold of the Schmitt trigger due to the voltage divider action of the resistor R1, R2 and VR1 This disables the gate of pin1 and due to this the transistor T2 goes into saturation while the transistor T1 is cut off therefore the green LED glows while the red segment goes off and the display will now glow as “C”
Circuit Diagram
VR1 is a miniature preset which is to be calibrated before use its calibrations are fairy simple, keep both the probes A and B short circuited and the preset VR1 at its minimum value and slowly increase the resistance value of the VR1 till the red LED glows OFF and only green LED glows
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