Tester for 74xx04 and 74xx14 ICs Circuit Diagram

The integrated circuits (ICs) 74xx04 and 74xx14 are very frequently used and reused during circuit design. Here xx stands for HC, HCT, AC and LS, etc. Sometimes, the internal inverters of these ICs get damaged. So, it is very important to test these ICs before initiating any experiment and sometimes during the experiments.

Presented here is a simple circuit which can test these ICs statically and dynamically.

Circuit and working
Fig. 1 shows the circuit diagram of a simple tester for 74xx04 and 74xx14 ICs. The circuit is built around hex inverter IC 74HC04 (IC1) and a few other components. You can also test a 74HC14 hex Schmitt trigger with this circuit.

Static testing. The jumpers J1 through J12 are used during static testing of the inverter IC. When J1 through J6 are closed, J7 through J12 should be kept open, and vice versa. When jumpers J1 through J6 are closed, the input of the corresponding inverter is high and the respective output is low. Then, LED1 through LED6 will glow. If jumpers J7 through J12 are closed, the input of the corresponding inverter is low and the respective output is high. Then, LED7 through LED12 will glow. If any one of the LEDs does not glow, it means that the corresponding gate is damaged.

Fig. 1: Circuit diagram of the simple tester for 74xx04 and 74xx14 ICs

Dynamic testing. During dynamic testing, jumpers J1 through J12 should be kept open. When jumpers J13 through J18 are closed, oscillations are generated on the output of each gate. The frequency varies from 0.5Hz to 10Hz. Here, both the LEDs will blink alternately. Their blinking frequency can be changed with VR1 to VR6, if needed.

If a gate’s (say, N2) output LEDs do not glow, it means that the gate’s (N2’s) segment is damaged.

IC 74xx04 may not oscillate during dynamic testing because it does not have specified internal Schmitt triggers. So, only IC 74xx14 can be checked dynamically. If all LEDs blink alternately, it means your 74xx14 is fine.

The circuit works on a 5V power supply but you can use a higher voltage supply, within limits specified in the datasheet.

Construction and testing
An actual-size, single-side PCB for the simple tester using a socket for the 74xx04 and 74xx14 ICs is shown in Fig. 2 and its component layout in Fig. 3. After assembling the circuit on PCB, enclose it in a suitable plastic case.

Fix two 6-pin connectors CON2 and CON3 for six outputs. Also fix 2-pin terminal connector CON1 for power supply. Jumpers J1 through J18 are used for external shorting. You have to use eighteen 2-pin berg strip male connectors on the PCB for shorting the jumpers. Fix presets VR1 through VR6 on the PCB for frequency control.

Fig. 2: An actual-size, single-side PCB for the simple tester for 74xx04 and 74xx14 ICs

  

 Fig. 3: Component layout for the PCB

If you want to test an IC, insert it in the 14-pin IC socket. Connectors CON2 and CON3 are provided on the PCB for testing the voltages at each individual gate. Before inserting IC in its socket, verify the test point voltages given in the table (only for inverter gate N1 given here). Similarly, you can verify other internal gates at the respective test points shown in the circuit diagram as well as in the PCB.

 Sourced By: EFY Author: Petre Tzv Petrov

Read More

Simple Circuit Board Checker

This little circuit indicates the basic integrity of a printed board, detecting 0V, positive supply voltage from less than 3V to 30V and floating parts. If the probe is floating, as it would be in a broken track, then both LEDs barely light up, since there is no current to drive the transistors, but if the probe touches 0V or a positive voltage one or other lights. A digital signal should light them in proportion to the mark-space ratio whereas the output of a circuit oscillating at a frequency rate below about 20Hz will cause the LEDs to flicker alternatively. The LEDs will illuminate always at a constant intensity, no matter the voltage supply used, because they are fed by a very simple FET constant-current generator (Q1).

Simple Circuit Board Checker  Circuit diagram

Circuit Board Checker Circuit Diagram

Parts:

R1 = 22K
R2 = 22K
D1 = Red LED
D2 = Green LED
Q1 = BF245
Q2 = BC547
Q3 = BC557

Notes:

• The Black clip must be connected to the negative ground of the board under test.
• The Red clip should be connected to a positive voltage source (not exceeding 30V) available on the same board.
• Metal probe is suitable for this circuit.
• Two Miniature Crocodile Clips (Red and Black) are also necessary.

Read More

Infra-red Remote Control Tester

As I was developing my IR Extender Circuit, I needed to find a way of measuring the relative intensities of different Infra red light sources. This circuit is the result of my research. I have used a photodiode, SFH2030 as an infra red sensor. A MOSFET opamp, CA3140 is used in the differential mode to amplify the pulses of current from the photodiode. LED1 is an ordinary coloured led which will light when IR radiation is being received.

The output of the opamp, pin 6 may be connected to a multimeter set to read DC volts. Infra red remote control strengths can be compared by the meter reading, the higher the reading, the stronger the infra red light. I aimed different remote control at the sensor from about 1 meter away when comparing results. For every microamp of current through the photodiode, about 1 volt is produced at the output. A 741 or LF351 will not work in this circuit. Although I have used a 12 volt power supply, a 9 volt battery will also work here.

Circuit diagram:

Read More

Temperature Monitor for Electronic Equipment

Build a Temperature Monitor for Electronic Equipment circuit diagram. As most electronics components’ characteristics vary with temperature, they are selected as per expected operating temperature range of the equipment. So it is important that the equipment stays within the temperature range for which it is designed.

This circuit warns when the temperature reaches predefined danger levels. Here the predefined levels are set to 45°C, 65°C, 85°C and 105°C, but one can set any other temperature levels to suit the equipment in use.Circuit and workingFig. 1 shows the temperature monitoring circuit. It is built around 10k NTC thermistor NTC1, shunt regulator TL431 (IC1), popular comparator LM324 (IC2) and some other components.

 Temperature Monitor for Electronic Equipment Circuit Diagram

IC2 activates corresponding LEDs (LED1 through LED4) when the temperature of thermistor NTC1 reaches the predefined level (refer Table I). The temperature is sensed by NTC1 and the produced corresponding voltage at point ‘A’ is fed to inverting terminal of all the four op-amps (A1 through A4). Switch S1 should be closed for this operation. This voltage level is compared with the reference voltage at non-inverting terminals of each op-amp. The reference voltage is obtained by voltage dividers from 2.5V reference source, which is produced using shunt regulator IC1. The reference voltage for each comparator can be set using presets VR1 through VR4.

The switches S2 through S6, together with resistors R2 through R6, are used for calibration purpose. For example, op-amp A4 of IC2 compares the voltage levels at point A (changing with change in temperature) with the reference voltage at its pin 12. The voltage level at pin 12 of A4 is adjusted with preset VR1. Switches S2 through S6 are used to simulate voltage levels corresponding to different temperatures.A4 is tuned for 45°C by keeping switch S3 in closed position and trimming preset VR1 until LED1 glows. S1 should be open during calibration. The same procedure is repeated for comparator A3, A2 and A1 to tune them for 65°C, 85°C and 105°C. Table I shows the presets and LEDs corresponding to each temperature level. After calibration, open switches S2 through S6.

Sourced By : EFY Author: Petre Tzv. Petrov

Read More

Simple Handy Tester Circuit Diagram

D. Mohan Kumar know as his best creations. For beginners, here’s a low-cost multitester that can be used to test the condition of almost all the electronic components For beginners, here’s a low-cost multitester that can be used to test the condition of almost all the electronic components from resistors to ICs. It uses only a few components but can also detect polarity, continuity, logic states and activity of multivibrators.

The circuit is extremely simple and exploits the biasing property of bipolar transistors. Transistors T1 and T2 act as transistor switches driving the red and green halves of bicolour LED1 independently to give results of the test.

 Simple Handy Tester Circuit Diagram

When power is applied by pressing switch S1, transistor T1 stops conducting due to the lack of forward bias. At the same time, transistor T2 takes base bias voltage from the battery through resistor R1 and conducts. This allows the red half of bicolour LED1 to illuminate.

When the base of transistor T1 gets positive voltage through resistor R3, it conducts to light up the green half of bicolour LED1. When transistor T1 conducts, the base of transistor T2 is grounded and it cuts off to turn off the red half of bicolour LED1. The functioning of the circuit thus depends on the signal obtained at the base of transistor T1. The table gives the testing procedures for various components with the expected indications/results.

Author: D. Mohn Kumar

Read More

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 I'm 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 don't let you car battery discharge... ;-)

author: Jonathan Filippi
e-mail: jonathan.filippi@virgilio.it

Read More