Simple Crystal Tester
https://www.electronics-lab.com/project/simple-crystal-tester/
Description Transistor Q1, a 2N3563, and its associated components form an oscillator circuit that will oscillate if, and only if, a good crystal is connected to the test clips. The output from the oscillator is then rectified by the 1N4148 signal diode and filtered by C3, a 100pF capacitor. The positive voltage developed across the […]
Transistor tester
https://www.electronics-lab.com/project/transistor-tester/
Description This is basically a high gain amplifier with feedback that causes the LED to flash at a rate determined by the 10u and 330k resistor. Remove one of the transistors and insert the unknown transistor. When it is NPN with the pins as shown in the photo, the LED will flash. To turn the […]
Logic Probe Plus
https://www.electronics-lab.com/project/logic-probe-plus/
This project is based on a probe logic states, capable of measuring levels from TTL (5v) to state levels of PLC’s (24v). For this we have employed the use of the PIC 12F683 microcontroller, which by its nature is capable of operating at low voltages, in this case 3vcc, besides having analog inputs and internal […]
Logic Probe
https://www.electronics-lab.com/project/logic-probe/
Description This circuit is a Logic Probe. It indicates the logic state of the node of any TTL logic circuit. To do that, we have to supply the probe with the same power of the circuit that we want to analyse: same Vcc and same GND. To check the logic level, we must connect the “Test” […]
Led display digital Voltmeter
https://www.electronics-lab.com/project/led-display-digital-voltmeter/
Copyright of this circuit belongs to Smart kit electronics. On this page, we will use this circuit to discuss improvements and we will introduce some changes based on the original schematic. General Description This is easy to build, but nevertheless very accurate and useful digital voltmeter. It has been designed as a panel meter and […]
Mosfet Tester
https://www.electronics-lab.com/project/mosfet-tester/
This is a variation on the astable multivibrator. Circuit was recently developed to test for N-mosfets (the power kind e.g irf830) I dont claim circuit can test all bad mosfets or all fault mosfet conditions. If mosfet is working it will operate in the astable multivibrator circuit causing the Led to flash. A bad […]
Phone Busy Indicator
https://www.electronics-lab.com/project/phone-busy-indicator/
Have you ever been using the modem or fax and someone else picks up the phone, breaking the connection? Well, this simple circuit should put an end to that. It signals that the phone is in use by lighting a red LED. When the phone is not in use, a green LED is lit. It […]
Phone line indicator
https://www.electronics-lab.com/project/phone-line-indicator/
Description With this circuit you can monitor your telephone line. You are able to detect if any telephone in the same line is busy with the help of a LED. This circuit does not affect the telephone’s line provider, so it’s trouble free but you use it at your own risk. It connects in parallel […]
Electronic Stethoscope
https://www.electronics-lab.com/project/electronic-stethoscope/
Circuit Description U1a operates as a low-noise microphone preamp. Its gain is only about 3.9 because the high output impedance of the drain of the FET inside the electret microphone causes U1as effective input resistor to be about 12.2K. C2 has a fairly high value in order to pass very low frequency (about 20 to […]
Plants Watering Watcher
https://www.electronics-lab.com/project/plants-watering-watcher/
Using a Veroboard mother-board about the same size as the battery holder, a daughter-board was added to hold the remaining parts. Schematic Parts List IC1 . CD74HC132 B1 … Two AAA alkaline cells, with holder C1, C3 1nF (0.001uF) or 2.2nF (0.0022uF) C2 … 100uF/16V electrolytic C4 … 220nF (0.22uF) R1 … 470K (all […]